| substrate specificity | A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts. (12 Dec 1998) |
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| substrate | <chemistry> A substance upon which an enzyme acts. Origin: L. Stratum = layer (18 Nov 1997) |
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| substrate cycle | <biochemistry> Any seqence of enzyme catalysed reactions in which the forward and reverse processes (catalysed by different enzymes) are consititutively active. Frequently used to describe the cycle of phosphorylation and dephosphorylation of phosphatidyl inositol derivatives in cell membranes. (05 Jan 1998) |
| substrate cycling | A set of opposing, nonequilibrium reactions catalyzed by different enzymes which act simultaneously, with at least one of the reactions driven by ATP hydrolysis. The results of the cycle are that ATP energy is depleted, heat is produced and no net substrate-to-product conversion is achieved. Examples of substrate cycling are cycling of gluconeogenesis and glycolysis pathways and cycling of the triglycerides and fatty acid pathways. Rates of substrate cycling may be increased many-fold in association with hypermetabolic states resulting from severe burns, cold exposure, hyperthyroidism, or acute exercise. (12 Dec 1998) |
| substrate inhibition | Inhibition of an enzyme activity by a substrate of the reaction catalyzed by that enzyme; often, this type of inhibition occurs at elevated substrate levels in which the substrate is binding to a second, non-active site on the enzyme. (05 Mar 2000) |
| substrate-level phosphorylation | Synthesis of high-energy phosphate bonds through reaction of inorganic phosphate with an activated (usually) organic substrate. (09 Oct 1997) |
| suicide substrate | A competitive inhibitor that is converted to an irreversible inhibitor at the active site of the enzyme. Synonym: mechanism-based inhibitor. (05 Mar 2000) |
| insulin receptor substrate-1 protein | <chemical> Amino acid sequence given in first source; a 180 kD protein that contains multiple phosphorylated tyrosine residues after insulin stimulation; human and rat forms (hirs-1 and irs-1) are homologous Synonym: insulin receptor substrate-1-like protein, irs-1 protein, irs-1 gene product, hirs-1 protein, hirs-1 gene product, insulin receptor substrate 1, insulin receptor substrate-1 (05 Dec 1998) |
| enzyme-substrate complex | A noncovalent complex of two molecules; often referring to the enzyme-substrate complex in an enzyme-catalyzed reaction. Compare: central complex, Michaelis complex. Synonym: enzyme-substrate complex. (05 Mar 2000) |
| analytical specificity | Freedom from interference by any element or compound other than the analyte. (05 Mar 2000) |
| antibody specificity | The property of antibodies which enables them to react with some antigenic determinants and not with others. Specificity is dependent on chemical composition, physical forces, and molecular structure at the binding site. (12 Dec 1998) |
| biological specificity | <biology, zoology> The specific, orderly patterns of development and metabolism which define and characterise an individual and its species. (21 Mar 1998) |
| relative specificity | The specificity of a medical screening test as determined by comparison with the same type of test (e.g., specificity of a new serological test relative to specificity of an established serological test). (05 Mar 2000) |
| sensitivity and specificity | Measures for assessing the results of diagnostic and screening tests. Sensitivity represents the proportion of truly diseased persons in a screened population who are identified as being diseased by the test. It is a measure of the probability of correctly diagnosing a condition. Specificity is the proportion of truly nondiseased persons who are so identified by the screening test. It is a measure of the probability of correctly identifying a nondiseased person. (12 Dec 1998) |
| species specificity | Restriction of a characteristic or response to the members of one species; it usually refers to that property of the immune response which differentiates one species from another on the basis of antigen recognition, but the concept is not limited to immunology and is used loosely at levels higher than the species. (12 Dec 1998) |
| specificity | The ability of the immune response to interact with individual antigens. (09 Oct 1997) |