Luca Turin

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Luca Turin
Born (1953-11-20) 20 November 1953 (age 67)
Occupationbiophysicist
Known for Vibration theory of olfaction

Luca Turin (born 20 November 1953) is a biophysicist and writer with a long-standing interest in bioelectronics, the sense of smell, perfumery, and the fragrance industry.

Contents

Early life and education

Turin was born in Beirut, Lebanon on 20 November 1953 into an Italian-Argentinian family, and raised in France, Italy and Switzerland. His father, Duccio Turin, was a UN diplomat and chief architect of the Palestinian refugee camps, [1] and his mother, Adela Turin (born Mandelli), is an art historian, designer, and award-winning children's author. [2] Turin studied Physiology and Biophysics at University College London and earned his PhD in 1978. [3] He worked at the CNRS from 1982-1992, and served as lecturer in Biophysics at University College London from 1992-2000.

Career

After leaving the CNRS, Turin first held a visiting research position at the National Institutes of Health in North Carolina [4] before moving back to London, where he became a lecturer in biophysics at University College London. In 2001 Turin was hired as CTO of start-up company Flexitral, based in Chantilly, Virginia, to pursue rational odorant design based on his theories. In April 2010 he described this role in the past tense, [5] and the company's domain name appears to have been surrendered. [6]

In 2010, Turin was based at MIT, working on a project to develop an electronic nose using natural receptors, financed by DARPA. [5] In 2014 he moved to the Institute of Theoretical Physics at the University of Ulm where he was a Visiting Professor. [7] He is a Stavros Niarchos Researcher [8] in the neurobiology division at the Biomedical Sciences Research Center Alexander Fleming in Greece. [9]

Vibration theory of olfaction

A major prediction of Turin's vibration theory of olfaction is the isotope effect: that the normal and deuterated versions of a compound should smell different due to unique vibration frequencies, despite having the same shape. A 2001 study by Haffenden et al. showed humans able to distinguish benzaldehyde from its deuterated version. [10]

However, experimental tests published in Nature Neuroscience in 2004 by Keller and Vosshall failed to support this prediction, with human subjects unable to distinguish acetophenone and its deuterated counterpart. [11] The study was accompanied by an editorial, which considered the work of Keller and Vosshall to be "refutation of a theory that, while provocative, has almost no credence in scientific circles." It continued, "The only reason for the authors to do the study, or for Nature Neuroscience to publish it, is the extraordinary -- and inappropriate -- degree of publicity that the theory has received from uncritical journalists." [12] The journal also published a review of The Emperor of Scent, calling Chandler Burr's book about Turin and his theory "giddy and overwrought." [13] However, tests with animals have shown fish and insects able to distinguish isotopes by smell. [14] [15] Biophysical simulations published in Physical Review Letters in 2007 suggest that Turin's proposal is viable from a physics standpoint. [16]

The vibration theory received possible support from a 2004 paper published in the journal Organic Biomolecular Chemistry by Takane and Mitchell, which shows that odor descriptions in the olfaction literature correlate more strongly with vibrational frequency than with molecular shape. [17]

In 2011, Turin and colleagues published a paper in PNAS showing drosophila fruit flies can distinguish between odorants and their deuterated counterparts. Tests on drosophila differ from human experiments by using an animal subject known to have a good sense of smell and free from psychological biases that may complicate human tests. [18] Drosophila were trained to avoid the deuterated odorant in a deuterated/normal pair, indicating a difference in odor. Furthermore, drosophila trained to avoid one deuterated odorant also avoided other deuterated odorants, chemically unrelated, indicating that the deuterated bond itself had a distinct smell. The authors identified a vibrational frequency that could be responsible and found it close to one found in nitriles. When flies trained to avoid deuterated odorants were exposed to the nitrile and its non-nitrile counterpart, the flies also avoided the nitrile, consistent with the theory that fly olfaction detects molecular vibrations. [19]

Two years later, in 2013, Turin and colleagues published a study in PLoS ONE showing that humans easily distinguish gas-chromatography-purified deuterated musk in double-blind tests. The team chose musks due to the high number of carbon-hydrogen bonds available for deuteration. They replicated the earlier results of Vosshall and Keller showing that humans cannot reliably distinguish between acetophenone and its deuterated counterpart, with 8 hydrogens, and showed that humans only begin to detect the isotope odor of the musks beginning at 14 deuteriums, or 50% deuteration. [20] Because Turin's proposed mechanism is a biological method of inelastic electron tunnelling spectroscopy, which exploits a quantum effect, his theory of olfaction mechanism has been described as an example of quantum biology. [21]

In response to Turin's 2013 paper, involving deuterated and undeuterated isotopomers of the musk cyclopentadecanone, [20] Block et al. in a 2015 paper in PNAS [22] report that the human musk-recognizing receptor, OR5AN1, identified using a heterologous olfactory receptor expression system and robustly responding to cyclopentadecanone and muscone (which has 30 hydrogens), fails to distinguish isotopomers of these compounds in vitro. Furthermore, the mouse (methylthio)methanethiol-recognizing receptor, MOR244-3, as well as other selected human and mouse olfactory receptors, responded similarly to normal, deuterated, and carbon-13 isotopomers of their respective ligands, paralleling results found with the musk receptor OR5AN1. Based on these findings, the authors conclude that the proposed vibration theory of olfaction does not apply to the human musk receptor OR5AN1, mouse thiol receptor MOR244-3, or other olfactory receptors examined. Additionally, theoretical analysis by the authors shows that the proposed electron transfer mechanism of the vibrational frequencies of odorants could be easily suppressed by quantum effects of nonodorant molecular vibrational modes. The authors conclude: "These and other concerns about electron transfer at olfactory receptors, together with our extensive experimental data, argue against the plausibility of the vibration theory." In commenting on this work, Vosshall writes "In PNAS, Block et al…. shift the "shape vs. vibration" debate from olfactory psychophysics to the biophysics of the ORs themselves. The authors mount a sophisticated multidisciplinary attack on the central tenets of the vibration theory using synthetic organic chemistry, heterologous expression of olfactory receptors, and theoretical considerations to find no evidence to support the vibration theory of smell." [23] While Turin comments that Block used "cells in a dish rather than within whole organisms" and that "expressing an olfactory receptor in human embryonic kidney cells doesn't adequately reconstitute the complex nature of olfaction...", Vosshall responds "Embryonic kidney cells are not identical to the cells in the nose .. but if you are looking at receptors, it's the best system in the world." [24] In a Letter to the Editor of PNAS, Turin et al. [25] raise concerns about Block et al. [22] and Block et al. respond. [26] A recent study [27] describes the responses of primary olfactory neurons in tissue culture to isotopes and finds that a small fraction of the population (<1%) clearly discriminates between isotopes, some even giving an all-or-or -none response to H or D isotopomers of octanal. The authors attribute this to "hypersensitivity" of some receptors to differences in hydrophobicity between normal and deuterated odorants.

Biological electronics

Turin filed one of the first patents for a semiconductor device made with protein. [28] Turin's recent work focuses on the relevance of his olfaction theory to more general mechanisms of G-protein coupled receptor activation. In an article [29] in Inference Review, he proposed that the electronic mechanism was a special case of a more general involvement of electron currents in GPCRs. A 2019 preprint [30] argues that the highest-resolution x-ray diffraction structure of rhodopsin, [31] considered the ancestor of all GPCRs, contains the elements of an electronic circuit. He has also reported detection of non-equilibrium electron spins in Drosophila by their radiofrequency emissions, [32] though this is described as a "work in progress".

Role in the case of Henri Korn

In 1988, Turin began work at the lab led by neuroscience researcher Henri Korn at the Pasteur Institute. There, Turin and his colleague Nicole Ropert reported to their superiors that they believed some of Korn's research on neurotransmitters was based on fabricated results. [33] After Turin made a formal request that the CNRS investigate the allegations, he was told to find work outside France; Ropert was also asked to leave. [34]

Korn was awarded the prestigious Richard Lounsbery Award in 1992 and became a member of the National Academy of Sciences in the U.S. and the French Academy of Sciences. [35] Then in 2007, re-analysis of Korn's data by Jacques Ninio in the Journal of Neurophysiology showed serious anomalies that suggested the results were indeed fabricated. [33]

Publications

Turin is the author of the book The Secret of Scent (2006), which details the history and science of his theory of olfaction, an acclaimed critical guide to perfume in French, Parfums: Le Guide, with two editions in 1992 and 1994, and is co-author of the English-language books Perfumes: The A-Z Guide (2008) and The Little Book of Perfumes (2011). He is also the subject of the 2002 book The Emperor of Scent by Chandler Burr [4] and the 1995 BBC Horizons documentary "A Code in the Nose."

Since 2003, Turin has also written a regular column on perfume, "Duftnote," for NZZ Folio, the German-language monthly magazine of Swiss newspaper Neue Zürcher Zeitung. The column is also published in English on the magazine's website. [36] The column ended in 2014. The collected columns are published as a book [37]

Awards and honors

In 2001 and 2004, Turin won the Prix Jasmin, the highest honor for perfume writing in France. He won the Jasmine Prize in the UK in 2009. [38]

Bibliography

Related Research Articles

Olfactory receptor neuron

An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system.

Olfactory receptors (ORs), also known as odorant receptors, are expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants which give rise to the sense of smell. Activated olfactory receptors trigger nerve impulses which transmit information about odor to the brain. These receptors are members of the class A rhodopsin-like family of G protein-coupled receptors (GPCRs). The olfactory receptors form a multigene family consisting of around 800 genes in humans and 1400 genes in mice.

Aroma compound Chemical compound that has a smell or odor

An aroma compound, also known as an odorant, aroma, fragrance or flavor, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficiently volatile for transmission via the air to the olfactory system in the upper part of the nose. As examples, various fragrant fruits have diverse aroma compounds, particularly strawberries which are commercially cultivated to have appealing aromas, and contain several hundred aroma compounds.

The docking theory of olfaction proposes that the smell of an odorant molecule is due to a range of weak non-covalent interactions between the odorant [a ligand] and its protein odorant receptor, such as electrostatic and Van der Waals interactions as well as H-bonding, dipole attraction, pi-stacking, metal ion, Cation–pi interaction, and hydrophobic effects, in addition to odorant conformation. While this type of recognition has previously been termed the shape theory of olfaction, which primarily considers molecular shape and size, this latter model is oversimplified since two scent molecules may have similar shapes and sizes but different sets of weak intermolecular forces and therefore activate different combinations of odorant receptors. Earlier “lock and key” and "hand in glove" models of protein−ligand binding has been replaced by a more nuanced pictures which consider the distortion of flexible molecules so as to form the optimal interactions with binding partners as in molecular docking of non-olfactory G-protein coupled receptors.

The vibration theory of smell proposes that a molecule's smell character is due to its vibrational frequency in the infrared range. This controversial theory is an alternative to the more widely accepted docking theory of olfaction, which proposes that a molecule's smell character is due to a range of weak non-covalent interactions between its protein odorant receptor, such as electrostatic and Van der Waals interactions as well as H-bonding, dipole attraction, pi-stacking, metal ion, Cation–pi interaction, and hydrophobic effects, in addition to the molecule's conformation.

Muscone

Muscone is an organic compound that is the primary contributor to the odor of musk.

The antennal lobe is the primary olfactory brain area in insects. The antennal lobe is a sphere-shaped deutocerebral neuropil in the brain that receives input from the olfactory sensory neurons in the antennae and mouthparts. Functionally, it shares some similarities with the olfactory bulb in vertebrates.

Olfactory fatigue, also known as odor fatigue, olfactory adaptation, and noseblindness, is the temporary, normal inability to distinguish a particular odor after a prolonged exposure to that airborne compound. For example, when entering a restaurant initially the odor of food is often perceived as being very strong, but after time the awareness of the odor normally fades to the point where the smell is not perceptible or is much weaker. After leaving the area of high odor, the sensitivity is restored with time. Anosmia is the permanent loss of the sense of smell, and is different from olfactory fatigue.

Hyperosmia is an increased olfactory acuity, usually caused by a lower threshold for odor. This perceptual disorder arises when there is an abnormally increased signal at any point between the olfactory receptors and the olfactory cortex. The causes of hyperosmia may be genetic, hormonal, environmental or the result of benzodiazepine withdrawal syndrome.

Quantum biology is the study of applications of quantum mechanics and theoretical chemistry to biological objects and problems. Many biological processes involve the conversion of energy into forms that are usable for chemical transformations, and are quantum mechanical in nature. Such processes involve chemical reactions, light absorption, formation of excited electronic states, transfer of excitation energy, and the transfer of electrons and protons in chemical processes, such as photosynthesis, olfaction and cellular respiration.

OR1A1

Olfactory receptor 1A1 is a protein that in humans is encoded by the OR1A1 gene.

OR7D4

Olfactory receptor 7D4 is a protein that in humans is encoded by the OR7D4 gene.

OR2J3

Olfactory receptor 2J3 is a protein that in humans is encoded by the OR2J3 gene.

Odor Volatilized chemical compounds that humans and animals can perceive by their sense of smell

An odor or odour is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive by their sense of smell. An odor is also called a "smell" or a "scent", which can refer to either a pleasant or an unpleasant odor.

Olfaction sense that detects odors

Olfaction, or the sense of smell, is the process of creating the perception of smell. It occurs when an odor binds to a receptor within the nose, transmitting a signal through the olfactory system. Olfaction has many purposes, including detecting hazards, pheromones, and plays a role in taste.

Olfactory memory refers to the recollection of odors. Studies have found various characteristics of common memories of odor memory including persistence and high resistance to interference. Explicit memory is typically the form focused on in the studies of olfactory memory, though implicit forms of memory certainly supply distinct contributions to the understanding of odors and memories of them. Research has demonstrated that the changes to the olfactory bulb and main olfactory system following birth are extremely important and influential for maternal behavior. Mammalian olfactory cues play an important role in the coordination of the mother infant bond, and the following normal development of the offspring. Maternal breast odors are individually distinctive, and provide a basis for recognition of the mother by her offspring.

Leslie B. Vosshall American neurobiologist

Leslie Birgit Vosshall, Ph.D., is an American neurobiologist and currently an HHMI Investigator and the Robin Chemers Neustein Professor of Neurogenetics and Behavior at The Rockefeller University. She is also the director of the Kavli Neural Systems Institute at The Rockefeller University. She is well known for her contributions to the field of olfaction, particularly for the discovery and subsequent characterization of the insect olfactory receptor family, and to the genetic basis of chemosensory behavior in mosquitoes and humans.

Or83b, also known as Orco, is an odorant receptor and the corresponding gene that encodes it. The odorant receptor Or83b is not exclusively expressed in insects. Though its actual function is still a mystery, the broadly expressed Or83b has been conserved across highly divergent insect populations across 250 million years of evolution.

Insect olfaction

Insect olfaction refers to the function of chemical receptors that enable insects to detect and identify volatile compounds for foraging, predator avoidance, finding mating partners and locating oviposition habitats. Thus, it is the most important sensation for insects. Most important insect behaviors must be timed perfectly which is dependent on what they smell and when they smell it. For example, olfaction is essential for hunting in many species of wasps, including Polybia sericea.

Eric Block American chemist

Eric Block is an American chemist whose research has focused on the chemistry of organosulfur and organoselenium compounds, Allium chemistry, and the chemistry of olfaction. As of 2018, he is Distinguished Professor of Chemistry Emeritus at the University at Albany, SUNY.

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