Vitamin A is a fat-soluble vitamin and an essential nutrient for animals. The term "vitamin A" encompasses a group of chemically related organic compounds that includes retinol, retinal, retinoic acid, and several provitamin (precursor) carotenoids, most notably beta-carotene. Vitamin A has multiple functions: it is essential for embryo development and growth, for maintenance of the immune system, and for vision, where it combines with the protein opsin to form rhodopsin – the light-absorbing molecule necessary for both low-light and color vision.
Lecithin–cholesterol acyltransferase is an enzyme, in many animals including humans, that converts free cholesterol into cholesteryl ester, which is then sequestered into the core of a lipoprotein particle, eventually making the newly synthesized HDL spherical and forcing the reaction to become unidirectional since the particles are removed from the surface. The enzyme is bound to high-density lipoproteins (HDLs) (alpha-LCAT) and LDLs (beta-LCAT) in the blood plasma. LCAT deficiency can cause impaired vision due to cholesterol corneal opacities, anemia, and kidney damage. It belongs to the family of phospholipid:diacylglycerol acyltransferases.
Phospholipase A1 (EC 3.1.1.32; systematic name: phosphatidylcholine 1-acylhydrolase) encoded by the PLA1A gene is a phospholipase enzyme which removes the 1-acyl group:
The visual cycle is a process in the retina that replenishes the molecule retinal for its use in vision. Retinal is the chromophore of most visual opsins, meaning it captures the photons to begin the phototransduction cascade. When the photon is absorbed, the 11-cis retinal photoisomerizes into all-trans retinal as it is ejected from the opsin protein. Each molecule of retinal must travel from the photoreceptor cell to the RPE and back in order to be refreshed and combined with another opsin. This closed enzymatic pathway of 11-cis retinal is sometimes called Wald's visual cycle after George Wald (1906–1997), who received the Nobel Prize in 1967 for his work towards its discovery.
In enzymology, a protein-glutamate O-methyltransferase is an enzyme that catalyzes the chemical reaction
The enzyme 11-cis-retinyl-palmitate hydrolase (EC 3.1.1.63) catalyzes the reaction
The enzyme retinoid isomerohydrolase (EC 3.1.1.64, all-trans-retinyl-palmitate hydrolase) catalyzes the reaction
In enzymology, a retinyl-palmitate esterase (EC 3.1.1.21) is an enzyme that catalyzes the chemical reaction
In enzymology, a 2-acylglycerophosphocholine O-acyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a phosphatidylcholine---sterol O-acyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a polysialic-acid O-acetyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a retinol O-fatty-acyltransferase is an enzyme that catalyzes the chemical reaction
Sterol O-acyltransferase is an intracellular protein located in the endoplasmic reticulum that forms cholesteryl esters from cholesterol.
In enzymology, a sphingomyelin synthase is an enzyme that catalyzes the chemical reaction
Retinol binding protein 1, cellular, also known as RBP1, is a protein that in humans is encoded by the RBP1 gene.
Triglyceride lipases are a family of lipolytic enzymes that hydrolyse ester linkages of triglycerides. Lipases are widely distributed in animals, plants and prokaryotes.
Retinol-binding protein 2 (RBP2) is a protein that in humans is encoded by the RBP2 gene.
Lecithin retinol acyltransferase is an enzyme that in humans is encoded by the LRAT gene.
2-acyl-sn-glycero-3-phosphocholines are a class of phospholipids that are intermediates in the metabolism of lipids. Because they result from the hydrolysis of an acyl group from the sn-1 position of phosphatidylcholine, they are also called 1-lysophosphatidylcholine. The synthesis of phosphatidylcholines with specific fatty acids occurs through the synthesis of 1-lysoPC. The formation of various other lipids generates 1-lysoPC as a by-product.
Retinol-binding proteins (RBP) are a family of proteins with diverse functions. They are carrier proteins that bind retinol. Assessment of retinol-binding protein is used to determine visceral protein mass in health-related nutritional studies.
