Enzymes committee

Hydroxymethylbilane Synthase (EC 2.5.1.61), HMBS HMBS (also known as porphobilinogen [PEG] deaminase) is a cytoplasmic enzyme that catalyzes the formation of one molecule of the linear tetrapyrrole 1-hydroxymethylbilane (HMB also known as preuroporphyrinogen) from four molecules of PEG with the release of four molecules of ammonia. The former enzyme committee designation for HMBS was EC 4.3.1.8, but in 2003 the enzyme was redesignated as EC 2.5.1.61. The enzyme has two molecules of its own substrate PEG, attached covalently to the apoenzyme as a prosthetic group. The enzyme is susceptible to allosteric inhibition by intermediates further down the heme biosynthetic pathway, notably coproporphyrinogen-III and protoporphyrinogen-IX. 

Expert Panel on Enzymes, Committee on Standards (IFCC) (1975), Clin. Chim. Acta, 61, F11-F24. 

The widely accepted basis of all enzyme classifications are the recommendations of the Enzyme Committee (E.C.) of the International Union of Biochemistry and Molecular Biology (IUBMB)1491. Within this system, enzymatic activities are classified by a four-level hierarchy and each entry is described by a set of four numbers. The first number describes the top level and can be either 1 for oxidoreductases, 2 for transferases, 3 for hydrolases, 4 for lyases, 5 for isomerases or 6 for ligases. The meaning of the three lower hierarchy levels depends on the top level group. As an example, glycogen synthase is classified as 2.4.1.11 here, the 2 stands for transferases, the 4 for glycosyl-transferases, the 1 for hexosyl-transferases and the 11 for the particular subfamily. 

International Union of Biochemistry and Molecular Biology Nomenclature Committee, 1992. Enzyme Nomenclature. New York Academic Press. A reference volume and glossary on die official classification and nomenclature of enzymes. 

IUB Nomenclature Committee, Enzyme Nomenclature , Academic Press, Orlando, Florida (1992). 

Joint FAOAVHO Expert Committee on Food Additives, Toxicological Evaluation of Some Food Colours, Enzymes, Flavour Enhancers, Thickening Agents, and Certain Other Food Additives, WHO Food Series, Geneva, 6, 74, 1975. 

The diagnosis of PK deficiency depends on the determination of quantitative enzyme activity or qualitative abnormalities of the enzyme. In 1979, the International Committee for Standardization in Haematology (ICSH) established methods for the biochemical characterization of red blood cell PK variants (M22). Since the establishment of these methods, many PK-deficient cases have been characterized, including 13 cases of homozygous PK deficiency. Residual red blood cell PK activity is not usually associated with phenotypic severity,whereas enzymatic characteristics such as decreased substrate affinity, thermal instability, or impaired response to the allosteric activator fructose-1,6-diphosphate (F-1,6-DP) correspond to a more severe phenotype. 

M26. Miwa, S., Luzzatto, L., Rosa, R., Paglia, D. E., Schroter, W De Flora, A., Fujii, H., Board, P. G and Beutler, E., International Committee for Standardization in Haematology Recommended methods for an additional red cell enzyme (pyrimidine 5 -nucleotidase) assay and the determination of red cell adenosine 5 -triphosphate, 2,3-diphosphoglycerate and reduced glutathione. Clin. Lab. Haematol. 11, 131-138 (1989). 

The responsibility for enzyme nomenclature is supported by the Nomenclature Committee of the International Union of Biochemistry (IUB now the International Union of Biochemistry and Molecular Biology, IUBMB) and the International Union of Pure and Applied Chemistry (IUPAC). These committees collect information about changes and additions to enzyme nomenclature13"15. 

Elevated blood pressure is common after ischemic stroke, and its treatment is associated with a decreased risk of stroke recurrence. The Joint National Committee and AHA/ASA guidelines recommend an angiotensin-converting enzyme inhibitor and a diuretic for reduction of blood pressure in patients with stroke or TIA after the acute period (first 7 days). Angiotensin II receptor blockers have also been shown to reduce the risk of stroke and should be considered in patients unable to tolerate angiotensinconverting enzyme inhibitors after acute ischemic stroke. 

Metofluthrin (I) The committee determined that the new data were sufficient to support a mitogenic mode of action for the development of liver tumors in rats exposed to metofluthrin in the carcinogenicity study. The report summarized mode of action study data that characterized effects such as increased P450 enzyme levels, increased smooth endoplasmic reticulum, hepatocellular hypertrophy, hepatocellular proliferation, and inhibition of intracellular communication, which were described as steps leading to tumor development via a nongenotoxic mechanism (i.e., mitogenicity). Some of these studies used sodium phenobarbital as a positive control,... 

This corresponds to the recommendations given in 1959 by a joint committee of the Clinical Chemistry Commission of IUPAC (International Union of Pure and Applied Chemistry) and the Enzyme Commission of IUB (International Union of Biochemistry). Thus, one unit of enzyme activity should be defined as that amount of enzyme which catalyzes the conversion of one micromole of substrate per minute under defined conditions (W9). 

The classification adopted by the Nomenclature Committee (NC) of the International Union of Biochemistry and Molecular Biology (IUBMB) divides peptidases into classes and subclasses according to the positional specificity in the cleavage of the peptide link of the substrate. The last publication of the complete printed version of the Enzyme Nomenclature was in 1992 [1][2], but a constantly updated version with supplements is available on the World Wide Web at http //www.chem.qmul.ac.uk/iubmb/enzyme/. Similarly, all available Protein Data Bank (PDB) entries classified as recommended by the NC-IUBMB can be found on the WWW at http //www.bio-chem.ucl.ac.uk/bsm/enzymes/. 

One of the general principles of the Nomenclature Committee is that enzymes should be classified and named according to the reaction they catalyze. However, the overlapping specificities of and great similarities in the action of different peptidases render naming solely on the basis of function impossible [10]. For example, some enzymes can act as both endo- and exopeptidases. Thus, cathepsin H (EC 3.4.22.16) is not only an endopeptidase but also acts as an aminopeptidase (EC 3.4.11), and cathepsin B (EC 3.4.22.1) acts as an endopeptidase as well as a peptidyl-dipeptidase (EC 3.4.15). The actual classification of peptidases is, therefore, a compromise based not only on the reaction catalyzed but also on the chemical nature of the catalytic site, on physiological function, and on historical priority. 

The classification system of the Enzyme Nomenclature Committee divides esterases into classes according to the type of ester bond they cleave (Table 2.4 see also Sect. 2.2.1) [1], The enzymes within these classes are further divided according to the nature of their preferred substrate(s). 

A selection of carboxylic ester hydrolases (EC 3.1.1) of major or more-modest significance in xenobiotic metabolism is given in Table 2.5. The recommendations of the Enzyme Nomenclature Committee on the classification of esterases cannot be considered completely satisfactory, but, even after decades of debate, a more satisfactory classification system remains to be proposed [56] [57], The main difficulties with esterase classification have been summarized as follows [58],... 

First, the true physiological substrates of most esterases are unknown. It is, therefore, hardly practicable to systematically name esterases according to the recommendations of the Enzyme Nomenclature Committee [1], i.e., based on the definite (physiological) role of the enzyme. The difficulty is that the use of nonphysiological substrates during purification and in characterization assays does not contribute to discovering the physiological role of an enzyme. 

Assays for endo-l,4- -glucanase [EC 3.2.1.4] (i.e., CMCase) and saccharifying cellulase (i.e., international filter paper U, IFPU) activities partially followed the methods recommended in the 1987 lUPAC report (65). When even undiluted enzyme samples fail to give the required glucose yield under prescribed assay conditions, the lUPAC committee recommends a less precise method. In the current study, cellulase activities in digester extracts were so low that the CMCU could only be defined as follows one CMC unit of activity was that amount of enzyme required to liberate one Hg glucose from CMC in 60 min. 

The ENZYME nomenclature database, a repository of information based on the recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB), currently contains 4435 enzyme entries (Release 38.0, September 2005). Of these, 545 entries are superseded, resulting in a final list of 3,890 enzymes, 224 sub-subclasses, and 65 subclasses. 

Since its foundation in 1956 the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB) has continually revised and updated the list of enzymes. Entries for new enzymes have been added, others have been deleted completely, or transferred to another EC number in the original class or to different EC classes, catalyzing other types of chemical reactions. The old numbers have not been allotted to new enzymes instead the place has been left vacant or cross-references given to the changes in nomenclature. 

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