Inactivation of Brain GABA transaminase by p$^1$, p$^2$-Bis(5′-pyridoxal) diphosphate

  • Jang, S.H. (Dept. of Genetic Engineering, Hallym Univ.) ;
  • Lee, B.R. (Dept. of Genetic Engineering, Hallym Univ.) ;
  • J.W. Hong (Dept. of Genetic Engineering, Hallym Univ.) ;
  • Park, K.W. (Dept. of Genetic Engineering, Hallym Univ.) ;
  • Yoo, B.K. (Dept. of Genetic Engineering, Hallym Univ.) ;
  • Cho, S.W. (Dept. of Biochemistry, College of Medicine, Univ. of Ulsan) ;
  • Park, S.Y. (Dept. of Genetic Engineering, Hallym Univ.)
  • Published : 1995.04.01

Abstract

GABA transaminase is inactivated by preincubation with p$^1$, p$^2$-bis(5'-pyridoxal) diphosphate at pH 7.0. The inactivation under pseudo-first order conditions proceeds at a slow rate (K$\_$obs/=0.035 min$\^$-1/). The degree of labeling of the enzyme by p$^1$, p$^2$-bis(5'-pyridoxal) diphosphate was determined by absorption spectroscopy, The blocking of 2 lysyl residues/dimer is needed for inactivation of the transaminase. The time course of the reaction is significantly affected by the substrate ${\alpha}$-ketoglutarate, which afforded complete protection against the loss of the catalytic activity. Whereas cofator pyridoxal phosphate failed to prevent the inactivation of the enzyme. Therefore, it is postulated that binding of ${\alpha}$-ketoglutarate tn lysyl residues is the major factor contributing to stabilization of the catalytic site and bifuctional reagent p$^1$, p$^2$bis(5'-pyridoxal) diphosphate blocks lysyl residues other than those involved in the binding of the cofactor.

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