Biomaterial Database

Evidence for the general base mechanism in carboxypeptidase A-catalyzed reactions: partitioning studies on nucleophiles and H2(18)O kinetic isotope effects. 1983

R Breslow, and J Chin, and D Hilvert, and G Trainor

Methanol does not detectably compete with water in carboxypeptidase-catalyzed cleavage of any substrate, although it is preferentially reactive in a model for the proposed nucleophilic mechanism for the enzyme that involves an anhydride intermediate. To test for such a common intermediate in the cleavage of related peptide and ester substrates, a method has been developed to examine H2(16)O-H2(18)O kinetic isotope-partitioning effects. The finding that benzoylglycylphenylalanine has an isotope effect of 1.019 +/- 0.002 while benzoylglycyl-beta-L-phenyl-lactate shows a small inverse isotope effect excludes most versions of a nucleophilic mechanism having a common anhydride intermediate. The bulk of the available evidence strongly favors the previously proposed general base mechanism.

UI	MeSH Term	Description	Entries
D007553	Isotope Labeling	Techniques for labeling a substance with a stable or radioactive isotope. It is not used for articles involving labeled substances unless the methods of labeling are substantively discussed. Tracers that may be labeled include chemical substances, cells, or microorganisms.	Isotope Labeling, Stable,Isotope-Coded Affinity Tagging,Isotopically-Coded Affinity Tagging,Affinity Tagging, Isotope-Coded,Affinity Tagging, Isotopically-Coded,Isotope Coded Affinity Tagging,Labeling, Isotope,Labeling, Stable Isotope,Stable Isotope Labeling,Tagging, Isotope-Coded Affinity,Tagging, Isotopically-Coded Affinity
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D010103	Oxygen Isotopes	Stable oxygen atoms that have the same atomic number as the element oxygen, but differ in atomic weight. O-17 and 18 are stable oxygen isotopes.	Oxygen Isotope,Isotope, Oxygen,Isotopes, Oxygen
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D002268	Carboxypeptidases	Enzymes that act at a free C-terminus of a polypeptide to liberate a single amino acid residue.	Carboxypeptidase
D013379	Substrate Specificity	A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.	Specificities, Substrate,Specificity, Substrate,Substrate Specificities
D043422	Carboxypeptidases A	Carboxypeptidases that are primarily found the DIGESTIVE SYSTEM that catalyze the release of C-terminal amino acids. Carboxypeptidases A have little or no activity for hydrolysis of C-terminal ASPARTIC ACID; GLUTAMIC ACID; ARGININE; LYSINE; or PROLINE. This enzyme requires ZINC as a cofactor and was formerly listed as EC 3.4.2.1 and EC 3.4.12.2.	Carboxypeptidase A,Carboxypeptidase A1,Carboxypeptidase A2,Carboxypeptidase A5,PCPA1 Enzyme,PCPA2 Enzyme,Procarboxypeptidase A,Procarboxypeptidase A1,Procarboxypeptidase A2