title: Interaction of aspartate aminotransferase with mercurochrome. Relationship of an exposed thiol group of the enzyme to the active centre.
abstract: Mercurochrome strongly inhibits aspartate transaminase and 2,3-dicarboxyethylated aspartate transaminase. The native enzyme exhibits a biphasic time-course of inactivation by mercurochrome with second-order rate constants 1.62 x 10(4) M-1 - min-1 and 2.15 x 10(3) M-1 - min-1, whereas the modified enzyme is inactivated more slowly (second-order rate constant 6.1 x 10(2) M-1 - min-1) under the same conditions. The inhibitor inactivates native and modified enzyme in the absence as well as in the presence of substrates. Mercurochrome-transaminase interaction is accompanied by a red shift in the absorption maximum of the fluorochrome of about 10 nm. Difference spectra of the mercurochrome-enzyme system versus mercurochrome, compared with analogous spectra of mercurochrome-ethanol, revealed that the spectral shifts recorded during mercurochrome-transaminase interaction are similar to those that occur when mercurochrome is dissolved in non-polar solvents. Studies of mercurochrome complexes with native or modified transaminase, isolated by chromatography on Sephadex G-25, revealed that native transaminase is able to conjugate with four mercurochrome molecules per molecule, but the modified enzyme is able to conjugate with only two mercurochrome molecules per molecule.
mesh_terms: D000818:Animals; D001219:Aspartate Aminotransferases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D003545:Cysteine; D003998:Dicarboxylic Acids; D005452:Fluoresceins / Q000494:pharmacology*; D007700:Kinetics; D008298:Maleates; D008622:Merbromin / Q000378:metabolism / Q000494:pharmacology*; D009206:Myocardium / Q000201:enzymology; D013057:Spectrum Analysis; D013552:Swine
chemical_list: D003998:Dicarboxylic Acids; D005452:Fluoresceins; D008298:Maleates; D001219:Aspartate Aminotransferases; D003545:Cysteine; D008622:Merbromin