Enzymes are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps. The study of enzymes is called enzymology and the field of pseudoenzyme analysis recognizes that during evolution, some enzymes have lost the ability to carry out biological catalysis, which is often reflected in their amino acid sequences and unusual 'pseudocatalytic' properties.
Ribonuclease is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within the EC 2.7 and 3.1 classes of enzymes.
Ribonuclease H is a family of non-sequence-specific endonuclease enzymes that catalyze the cleavage of RNA in an RNA/DNA substrate via a hydrolytic mechanism. Members of the RNase H family can be found in nearly all organisms, from bacteria to archaea to eukaryotes.
Ribonuclease L or RNase L, known sometimes as ribonuclease 4 or 2'-5' oligoadenylate synthetase-dependent ribonuclease, is an interferon (IFN)-induced ribonuclease which, upon activation, destroys all RNA within the cell. RNase L is an enzyme that in humans is encoded by the RNASEL gene.
Angiogenin (ANG) also known as ribonuclease 5 is a small 123 amino acid protein that in humans is encoded by the ANG gene. Angiogenin is a potent stimulator of new blood vessels through the process of angiogenesis. Ang hydrolyzes cellular RNA, resulting in modulated levels of protein synthesis and interacts with DNA causing a promoter-like increase in the expression of rRNA. Ang is associated with cancer and neurological disease through angiogenesis and through activating gene expression that suppresses apoptosis.
Ribonuclease P is a type of ribonuclease which cleaves RNA. RNase P is unique from other RNases in that it is a ribozyme – a ribonucleic acid that acts as a catalyst in the same way that a protein-based enzyme would. Its function is to cleave off an extra, or precursor, sequence of RNA on tRNA molecules. Further, RNase P is one of two known multiple turnover ribozymes in nature, the discovery of which earned Sidney Altman and Thomas Cech the Nobel Prize in Chemistry in 1989: in the 1970s, Altman discovered the existence of precursor tRNA with flanking sequences and was the first to characterize RNase P and its activity in processing of the 5' leader sequence of precursor tRNA. Recent findings also reveal that RNase P has a new function. It has been shown that human nuclear RNase P is required for the normal and efficient transcription of various small noncoding RNAs, such as tRNA, 5S rRNA, SRP RNA and U6 snRNA genes, which are transcribed by RNA polymerase III, one of three major nuclear RNA polymerases in human cells.
Bovine pancreatic ribonuclease, also often referred to as bovine pancreatic ribonuclease A or simply RNase A, is a pancreatic ribonuclease enzyme that cleaves single-stranded RNA. Bovine pancreatic ribonuclease is one of the classic model systems of protein science. Two Nobel Prizes in Chemistry have been awarded in recognition of work on bovine pancreatic ribonuclease: in 1972, the Prize was awarded to Christian Anfinsen for his work on protein folding and to Stanford Moore and William Stein for their work on the relationship between the protein's structure and its chemical mechanism; in 1984, the Prize was awarded to Robert Bruce Merrifield for development of chemical synthesis of proteins.
Ribonuclease inhibitor (RI) is a large (~450 residues, ~49 kDa), acidic (pI ~4.7), leucine-rich repeat protein that forms extremely tight complexes with certain ribonucleases. It is a major cellular protein, comprising ~0.1% of all cellular protein by weight, and appears to play an important role in regulating the lifetime of RNA.
Ribonuclease III (RNase III or RNase C)(BRENDA 3.1.26.3) is a type of ribonuclease that recognizes dsRNA and cleaves it at specific targeted locations to transform them into mature RNAs. These enzymes are a group of endoribonucleases that are characterized by their ribonuclease domain, which is labelled the RNase III domain. They are ubiquitous compounds in the cell and play a major role in pathways such as RNA precursor synthesis, RNA Silencing, and the pnp autoregulatory mechanism.
Drosha is a Class 2 ribonuclease III enzyme that in humans is encoded by the DROSHA gene. It is the primary nuclease that executes the initiation step of miRNA processing in the nucleus. It works closely with DGCR8 and in correlation with Dicer. It has been found significant in clinical knowledge for cancer prognosis and HIV-1 replication.
In molecular biology, nuclear ribonuclease P is a ubiquitous endoribonuclease, found in archaea, bacteria and eukarya as well as chloroplasts and mitochondria. Its best characterised enzyme activity is the generation of mature 5′-ends of tRNAs by cleaving the 5′-leader elements of precursor-tRNAs. Cellular RNase Ps are ribonucleoproteins. The RNA from bacterial RNase P retains its catalytic activity in the absence of the protein subunit, i.e. it is a ribozyme. Similarly, archaeal RNase P RNA has been shown to be weakly catalytically active in the absence of its respective protein cofactors. Isolated eukaryotic RNase P RNA has not been shown to retain its catalytic function, but is still essential for the catalytic activity of the holoenzyme. Although the archaeal and eukaryotic holoenzymes have a much greater protein content than the bacterial ones, the RNA cores from all three lineages are homologous—the helices corresponding to P1, P2, P3, P4, and P10/11 are common to all cellular RNase P RNAs. Yet there is considerable sequence variation, particularly among the eukaryotic RNAs.
Pancreatic ribonuclease family is a superfamily of pyrimidine-specific endonucleases found in high quantity in the pancreas of certain mammals and of some reptiles.
Amphinase is a ribonuclease enzyme found in the oocytes of the Northern leopard frog (Rana pipiens). Amphinase is a member of the pancreatic ribonuclease protein superfamily and degrades long RNA substrates. Along with ranpirnase, another leopard frog ribonuclease, amphinase has been studied as a potential cancer therapy due to its unusual mechanism of cytotoxicity tested against tumor cells.
RNase R, or Ribonuclease R, is a 3'-->5' exoribonuclease, which belongs to the RNase II superfamily, a group of enzymes that hydrolyze RNA in the 3' - 5' direction. RNase R has been shown to be involved in selective mRNA degradation, particularly of non stop mRNAs in bacteria. RNase R has homologues in many other organisms.
The degradosome is a multiprotein complex present in most bacteria that is involved in the processing of ribosomal RNA and the degradation of messenger RNA and is regulated by Non-coding RNA. It contains the proteins RNA helicase B, RNase E and Polynucleotide phosphorylase.
Ribonuclease pancreatic is an enzyme that in humans is encoded by the RNASE1 gene.
Ribonuclease 4 is an enzyme that in humans is encoded by the RNASE4 gene.
Bovine seminal RNase (BS-RNase) is a member of the ribonuclease superfamily produced by the bovine seminal vesicles. This enzyme can not be differentiated from its members distinctly since there are more features that this enzyme shares with its family members than features that it possess alone. The research on the question of how new functions arrive in proteins in evolution led the scientists to find an uncommon consequence for a usual biological event called gene conversion in the case of the ribonuclease (RNase) protein family. The most well-known member of this family, RNase A, is expressed in the pancreas of oxen. It serves to digest RNA in intestine, and evolved from bacteria fermenting in the stomach of the first ox. The homologous RNase, called seminal RNase, differs from RNase A by 23 amino acids and is expressed in seminal plasma in the concentration of 1-1.5 mg/ml, which constitutes more than 3% of the fluid protein content. Bovine seminal ribonuclease (BS-RNase) is a homologue of RNase A with specific antitumor activity.
Ribonuclease E is a bacterial ribonuclease that participates in the processing of ribosomal RNA and the chemical degradation of bulk cellular RNA.
The retroviral ribonuclease H is a catalytic domain of the retroviral reverse transcriptase (RT) enzyme. The RT enzyme is used to generate complementary DNA (cDNA) from the retroviral RNA genome. This process is called reverse transcription. To complete this complex process, the retroviral RT enzymes need to adopt a multifunctional nature. They therefore possess 3 of the following biochemical activities: RNA-dependent DNA polymerase, ribonuclease H, and DNA-dependent DNA polymerase activities. Like all RNase H enzymes, the retroviral RNase H domain cleaves DNA/RNA duplexes and will not degrade DNA or unhybridized RNA.
