RESUMEN
The amine specificity of guinea pig liver transglutaminase, a model enzyme for endo-gamma-glutamine:epsilon-lysin transferases, was explored with the aid of synthetic substrates of high apparent affinities. As exemplified by dansyl- (5-dimethylamino-1-naphthalenesulfonyl), (2,4-dinitrobenzenesulfonyl)-, and (2,4,6-triisopropylbenzenesulfonyl)-cadaverines--each of which showed affinities of approximately 4 x 10(7) M-1--the best amine substrates carried a large hydrophobic substituent attached to an alkylamine side chain of about 7.2 A in length. Altogether, our results point to the importance of a hydrophobic binding region in the enzyme from where the alkyl side chain reaches into a narrow crevice toward the active center and positions the primary amine of the substrate for attacking the carbonyl group of the acyl enzyme intermediate.
Asunto(s)
Hígado/enzimología , gamma-Glutamiltransferasa/metabolismo , Aminas/síntesis química , Animales , Cobayas , Cinética , Especificidad por SustratoRESUMEN
gamma,gamma'-(4,4'-Diamino-3,3'-biphenylylenedioxy)dibutyric acid (dicarboxidine) is a new chromogen developed as a safe substitute for conventional benzidine type reagents. The compound is water soluble and has a low distribution ratio organic phase/aqueous phase, which makes it superior for use with automatic analytical instruments. The stability of both dicarboxidine and its coloured oxidized form are better than and their sensitivity equal to that of o-dianisidine. Dicarboxidine is not mutagenic in Ames test. Studies in mice for two years failed to reveal any carcinogenic activity, studies in rats indicated only a marginal effect.