Chymotrypsin (EC 3.4.21.1, chymotrypsins A and B, alpha-chymar ophth, avazyme, chymar, chymotest, enzeon, quimar, quimotrase, alpha-chymar, alpha-chymotrypsin A, alpha-chymotrypsin) is a digestive enzyme component of pancreatic juice acting in the duodenum, where it performs proteolysis, the breakdown of proteins and polypeptides. Chymotrypsin preferentially cleaves peptide amide bonds where the side chain of the amino acid N-terminal to the scissile amide bond (the P1 position) is a large hydrophobic amino acid (tyrosine, tryptophan, and phenylalanine). These amino acids contain an aromatic ring in their side chain that fits into a hydrophobic pocket (the S1 position) of the enzyme. It is activated in the presence of trypsin. The hydrophobic and shape complementarity between the peptide substrate P1 side chain and the enzyme S1 binding cavity accounts for the substrate specificity of this enzyme. Chymotrypsin also hydrolyzes other amide bonds in peptides at slower rates, particularly those containing leucine at the P1 position.
Histone acetyltransferases (HATs) are enzymes that acetylate conserved lysine amino acids on histone proteins by transferring an acetyl group from acetyl-CoA to form ε-N-acetyllysine. DNA is wrapped around histones, and, by transferring an acetyl group to the histones, genes can be turned on and off. In general, histone acetylation increases gene expression.
The peptidyl transferase is an aminoacyltransferase as well as the primary enzymatic function of the ribosome, which forms peptide bonds between adjacent amino acids using tRNAs during the translation process of protein biosynthesis. The substrates for the peptidyl transferase reaction are two tRNA molecules, one bearing the growing peptide chain and the other bearing the amino acid that will be added to the chain. The peptidyl chain and the amino acids are attached to their respective tRNAs via ester bonds to the O atom at the CCA-3' ends of these tRNAs. Peptidyl transferase is an enzyme that catalyzes the addition of an amino acid residue in order to grow the polypeptide chain in protein synthesis. It is located in the large ribosomal subunit, where it catalyzes the peptide bond formation. It is composed entirely of RNA. The alignment between the CCA ends of the ribosome-bound peptidyl tRNA and aminoacyl tRNA in the peptidyl transferase center contribute to its ability to catalyze these reactions. This reaction occurs via nucleophilic displacement. The amino group of the aminoacyl tRNA attacks the terminal carboxyl group of the peptidyl tRNA. Peptidyl transferase activity is carried out by the ribosome. Peptidyl transferase activity is not mediated by any ribosomal proteins but by ribosomal RNA (rRNA), a ribozyme. Ribozymes are the only enzymes which are not made up of proteins, but ribonucleotides. All other enzymes are made up of proteins. This RNA relic is the most significant piece of evidence supporting the RNA World hypothesis.
Acetyl-CoA carboxylase (ACC) is a biotin-dependent enzyme that catalyzes the irreversible carboxylation of acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT). ACC is a multi-subunit enzyme in most prokaryotes and in the chloroplasts of most plants and algae, whereas it is a large, multi-domain enzyme in the cytoplasm of most eukaryotes. The most important function of ACC is to provide the malonyl-CoA substrate for the biosynthesis of fatty acids. The activity of ACC can be controlled at the transcriptional level as well as by small molecule modulators and covalent modification. The human genome contains the genes for two different ACCs—ACACA and ACACB.
Carnitine palmitoyltransferase II deficiency, sometimes shortened to CPT-II or CPT2, is an autosomal recessively inherited genetic metabolic disorder characterized by an enzymatic defect that prevents long-chain fatty acids from being transported into the mitochondria for utilization as an energy source. The disorder presents in one of three clinical forms: lethal neonatal, severe infantile hepatocardiomuscular and myopathic.
A catalytic triad is a set of three coordinated amino acids that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes. An acid-base-nucleophile triad is a common motif for generating a nucleophilic residue for covalent catalysis. The residues form a charge-relay network to polarise and activate the nucleophile, which attacks the substrate, forming a covalent intermediate which is then hydrolysed to release the product and regenerate free enzyme. The nucleophile is most commonly a serine or cysteine amino acid, but occasionally threonine or even selenocysteine. The 3D structure of the enzyme brings together the triad residues in a precise orientation, even though they may be far apart in the sequence.
Dihydrolipoyl transacetylase is an enzyme component of the multienzyme pyruvate dehydrogenase complex. The pyruvate dehydrogenase complex is responsible for the pyruvate decarboxylation step that links glycolysis to the citric acid cycle. This involves the transformation of pyruvate from glycolysis into acetyl-CoA which is then used in the citric acid cycle to carry out cellular respiration.
An oxyanion hole is a pocket in the active site of an enzyme that stabilizes transition state negative charge on a deprotonated oxygen or alkoxide. The pocket typically consists of backbone amides or positively charged residues. Stabilising the transition state lowers the activation energy necessary for the reaction, and so promotes catalysis. For example, proteases such as chymotrypsin contain an oxyanion hole to stabilise the tetrahedral intermediate anion formed during proteolysis and protects substrate's negatively charged oxygen from water molecules. Additionally, it may allow for insertion or positioning of a substrate, which would suffer from steric hindrance if it could not occupy the hole. Enzymes that catalyse multi-step reactions can have multiple oxyanion holes that stabilise different transition states in the reaction.
Carnitine O-palmitoyltransferase is a mitochondrial transferase enzyme involved in the metabolism of palmitoylcarnitine into palmitoyl-CoA. A related transferase is carnitine acyltransferase.
Carnitine palmitoyltransferase I (CPT1) also known as carnitine acyltransferase I, CPTI, CAT1, CoA:carnitine acyl transferase (CCAT), or palmitoylCoA transferase I, is a mitochondrial enzyme responsible for the formation of acyl carnitines by catalyzing the transfer of the acyl group of a long-chain fatty acyl-CoA from coenzyme A to l-carnitine. The product is often Palmitoylcarnitine, but other fatty acids may also be substrates. It is part of a family of enzymes called carnitine acyltransferases. This "preparation" allows for subsequent movement of the acyl carnitine from the cytosol into the intermembrane space of mitochondria.
Pantothenate kinase (EC 2.7.1.33, PanK; CoaA) is the first enzyme in the Coenzyme A (CoA) biosynthetic pathway. It phosphorylates pantothenate (vitamin B5) to form 4'-phosphopantothenate at the expense of a molecule of adenosine triphosphate (ATP). It is the rate-limiting step in the biosynthesis of CoA.
In enzymology, a steroid Δ5-isomerase is an enzyme that catalyzes the chemical reaction
In enzymology, an acetyl-CoA C-acetyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a [acyl-carrier-protein] S-acetyltransferase is an enzyme that catalyzes the reversible chemical reaction
Carnitine O-octanoyltransferase is a member of the transferase family, more specifically a carnitine acyltransferase, a type of enzyme which catalyzes the transfer of acyl groups from acyl-CoAs to carnitine, generating CoA and an acyl-carnitine. The systematic name of this enzyme is octanoyl-CoA:L-carnitine O-octanoyltransferase. Other names in common use include medium-chain/long-chain carnitine acyltransferase, carnitine medium-chain acyltransferase, easily solubilized mitochondrial carnitine palmitoyltransferase, and overt mitochondrial carnitine palmitoyltransferase. Specifically, CROT catalyzes the chemical reaction:
In enzymology, formate C-acetyltransferase is an enzyme. Pyruvate formate lyase is found in Escherichia coli and other organisms. It helps regulate anaerobic glucose metabolism. Using radical non-redox chemistry, it catalyzes the reversible conversion of pyruvate and coenzyme-A into formate and acetyl-CoA. The reaction occurs as follows:
In enzymology, glucosamine-phosphate N-acetyltransferase (GNA) is an enzyme that catalyzes the transfer of an acetyl group from acetyl-CoA to the primary amine in glucosamide-6-phosphate, generating a free CoA and N-acetyl-D-glucosamine-6-phosphate.
In enzymology, a homocitrate synthase (EC 2.3.3.14) is an enzyme that catalyzes the chemical reaction
In enzymology, a maltose O-acetyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a serine C-palmitoyltransferase (EC 2.3.1.50) is an enzyme that catalyzes the chemical reaction:
