The catalytic site of Escherichia coli aspartate transcarbamylase: interaction between histidine 134 and the carbonyl group of the substrate carbamyl phosphate. Academic Article uri icon

Overview

abstract

  • Previous pKa determinations indicated that histidine 134, present in the catalytic site of aspartate transcarbamylase, might be the group involved in the binding of the substrate carbamyl phosphate and, possibly, in the catalytic efficiency of this enzyme. In the present work, this residue was replaced by an asparagine through site-directed mutagenesis. The results obtained show that histidine 134 is indeed the group of the enzyme whose deprotonation increases the affinity of the catalytic site for carbamyl phosphate. In the wild-type enzyme this group can be titrated only by those carbamyl phosphate analogues that bear the carbonyl group. In the modified enzyme the group whose deprotonation increases the catalytic efficiency is still present, indicating that this group is not the imidazole ring of histidine 134 (pKa = 6.3). In addition, the pKa of the still unknown group involved in aspartate binding is shifted by one unit in the mutant as compared to the wild type.

publication date

  • September 11, 1990

Research

keywords

  • Aspartate Carbamoyltransferase
  • Bacterial Proteins
  • Carbamyl Phosphate
  • Escherichia coli

Identity

Scopus Document Identifier

  • 0025180356

Digital Object Identifier (DOI)

  • 10.1021/bi00488a041

PubMed ID

  • 2252907

Additional Document Info

volume

  • 29

issue

  • 36