Regulation of Thiamine Biosynthesis in Escherichia coli*

Publisher Website
Google Scholar
Abstract
The four enzymes, which are involved in thiamine biosynthesis from the pyrimidine and thiazole moieties of thiamine, are repressible and derepressible in Escherichia coli depending upon the intracellular thiamine concentration variable under different growth conditions. In a mutant of E. coli W requiring the thiazole moiety of thiamine for growth, fully derepressed levels of the four enzymes were brought about by thiamine at 5μm in the cell fluid which resulted from addition of 0.01μm thiamine to a minimal growth medium; 0.05μm thiamine in the growth medium resulted in 70% reduction of the activities of hydroxymethylpyrimidine kinase [EG 2.7.1.49], phosphohydroxymethyl-pyrimidine kinase [EC 2.7.4.7], and thiamincphosphate pyrophosphorylase [EG 2.5.1.3], and 40% reduction of hydroxyethylthiazole kinase [EG 2.7.1.50] activity at 18μm cellular thiamine concentration. Activities of the four enzymes were not detectable at a cellular thiamine level of 35μm when either the mutant of E. coli W or a wild strain of E. coli K12 was grown in the presence of 0.1μm thiamine. Evidence is presented to indicate that the reduction in the enzyme activities is due to repression of the enzyme formations, but not due to feedback inhibition of the enzyme activities. Adcnine in the growth medium caused derepression of the four enzymes involved in thiamine synthesis in E. coli K12 by lowering the thiamine level in the cells. The cells of E. coli K12 grown in the presence of L-phenylalanine contained derepressed levels of the four enzymes in thiamine synthesis, accompanied with an increase of the cellular thiamine level. The possible mechanism for the paradoxical effect of L-phenylalanine on thiamine synthesis and thiamine content was discussed.

This publication has 0 references indexed in Scilit: