| respiratory enzyme complexes | <biochemistry> The enzymes that make up the respiratory chain: NADH Q reductase, succinate Q reductase, cytochrome reductase, cytochrome C and cytochrome oxidase. (18 Nov 1997) |
|---|---|
| glycogen debranching enzyme system | 1,4-alpha-d-glucan-1,4-alpha-d-glucan 4-alpha-d-glucosyltransferase/dextrin 6 alpha-d-glucanohydrolase. An enzyme system having both 4-alpha-glucanotransferase (ec 2.4.1.25) and amylo-1,6-glucosidase (ec 3.2.1.33) activities. As a transferase it transfers a segment of a 1,4-alpha-d-glucan to a new 4-position in an acceptor, which may be glucose or another 1,4-alpha-d-glucan. As a glucosidase it catalyses the endohydrolysis of 1,6-alpha-d-glucoside linkages at points of branching in chains of 1,4-linked alpha-d-glucose residues. Amylo-1,6-glucosidase activity is deficient in glycogen storage disease type III. (12 Dec 1998) |
| restriction enzyme | <enzyme, molecular biology> Class of bacterial enzymes that cut DNA at specific sites. In bacteria their function is to destroy foreign DNA, such as that of bacteriophages (host DNA is specifically modified at these sites). Type I restriction endonucleases occur as a complex with the methylase and a polypeptide that binds to the recognition site on DNA. They are often not very specific and cut at a remote site. Type II restriction endonucleases are the classic experimental tools. They have very specific recognition and cutting sites. The recognition sites are short, 4-8 nucleotides and are usually palindromic sequences. Because both strands have the same sequence running in opposite directions the enzymes make double stranded breaks, which, if the site of cleavage is off centre, generates fragments with short single stranded tails, these can hybridise to the tails of other fragments and are called sticky ends. They are generally named according to the bacterium from which they were isolated (first letter of genus name and the first two letters of the specific name). The bacterial strain is identified next and multiple enzymes are given Roman numerals. For example the two enzymes isolated from the R strain of E. Coli are designated Eco RI and Eco RII. (10 Mar 1998) |
| restriction enzyme cutting site | <molecular biology> A specific nucleotide sequence of DNA at which a particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (for example, every several hundred basepairs), others much less frequently (rare-cutter, for example, every 10,000 base pairs). (10 Mar 1998) |
| restriction enzyme, endonuclease | A protein that recognises specific, short nucleotide sequences and cuts DNA at those sites. Bacteria contain over 400 such enzymes that recognise and cut over 100 different DNA sequences. See restriction enzyme cutting site. (05 Mar 2000) |
| P enzyme | <enzyme> Enzyme that catalyses the sequential removal of glycosyl residues from glycogen to yield one glucose-1-phosphate per reaction. Its activity is controlled by phosphorylation (by phosphorylase kinase). (21 Jun 2000) |
| membrane enzyme | <enzyme> An enzyme present or embedded in a biomembrane. (05 Mar 2000) |
| RNA enzyme | <molecular biology> Often referred to as RNA with catalytic capacity, an enzyme made of nucleic acid not protein that catalyse chemical reactions, often the breakdown of other RNAs. Of particular interest because of the implications for self replicating systems in the earliest stages of the evolution of (terrestrial) life. Their discovery in the mid-1980s refuted the concept that only proteins could be biological catalysts. There is potential for their use as pharmaceuticals and industrial catalysts. (13 Nov 1997) |
| methionine-activating enzyme | <enzyme> An enzyme that catalyses the synthesis of s-adenosylmethionine from methionine and ATP. Chemical name: ATP:L-methionine S-adenosyltransferase Registry number: EC 2.5.1.6 (12 Dec 1998) |
| microparticle enzyme immunoassay | A technique in which the solid-phase support consists of very small microparticles in liquid suspension. Specific reagent antibodies are covalently bound to the microparticles. Antigen, if present, is then "sandwiched" between bound antibodies and antigen-specific, enzyme-labelled antibodies. Antigen-antibody complexes are detected and quantitated by analysis of fluorescence from the enzyme-substrate interaction. Acronym: MEIA (05 Mar 2000) |
| citrate cleavage enzyme | ATP citrate (pro-3S)-lyase |
| phosphorylase-rupturing enzyme | <enzyme> An enzyme that deactivates glycogen phosphorylase a by releasing inorganic phosphate and phosphorylase b, the inactive form. Chemical name: (Phosphorylase a) phosphohydrolase Registry number: EC 3.1.3.17 (12 Dec 1998) |
| photoreactivating enzyme | deoxyribodipyrimidine photolyase |
| modification enzyme | <enzyme, molecular biology> An enzyme that introduces minor bases into DNA or RNA or that alters bases already incorporated. Serves to alter the sequence so that restriction enzymes will not damage the strand. (18 Nov 1997) |
| Warburg's old yellow enzyme | <enzyme> A flavoprotein that reversibly oxidises NADPH to NADP and a reduced acceptor. Chemical name: NADPH:(acceptor) oxidoreductase Registry number: EC 1.6.99.1 (12 Dec 1998) |