Author:
Grimminger H,Umbarger H E
Abstract
Several properties of the three acetohydroxy acid synthases of Escherichia coli have been compared in crude extracts. The three enzymes can be readily distinguished from each other. Acetohydroxy acid synthase I, the product of the ilvB gene, has been purified to near homogeneity. The purification was made possible by the fact that the enzyme was maintained in buffers of a high ionic strength or in buffers containing glycerol. Density gradient centrifugation studies indicated that the enzyme exists as a dimer of subunits of similar (60,000) molecular weight in buffers containing glycerol with or without two of the cofactors. Mg2+ and thiamine diphosphate. When flavine adenine dinucleotide was added along with Mg2+ and thiamine diphosphate, an increase in the rate of sedimentation occurred that was thought to be due to a rapid tetramer-dimer interconversion. The addition of pyruvate, the substrate, along with the three cofactors, resulted in a further increase in sedimentation rate, due presumably to an increase in the tetramer-to-dimer ratio. The addition of valine to the complete system resulted in maintenance of the enzyme in the dimeric state concomitant with inhibition of enzyme activity.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
78 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献