Thiamine uptake in Escherichia coli: III. Regulation of thiamine uptake in Escherichia coli

Abstract

The metabolic regulation of thiamine uptake in Escherichia coli has been investigated. A thiamine regulatory mutant (PT-R1), which is three times higher in cellular thiamine concentration than the parent E. coli K12 and contains a normal level of the membrane thiamine kinase (ATP: thiamine pyrophosphotransferase, EC 2.7.6.2), showed the rate of thiamine uptake half that of the parent strain. This reduction in the rate of thiamine uptake in PT-R1 is not attributable to alterations in the activity and specificity of the thiamine transport system, to an increase in the exit rate of thiamine nor to feedback inhibition. The results obtained with PT-R1 suggest that formation of the transport system is repressed by the enhanced cellular thiamine in this mutant. Evidence has been obtained which shows that the rate of thiamine uptake by cells of various E. coli strains grown in an excess of thiamine was reduced with an increase in the cellular thiamine concentration. Adenine in the growth medium, which is known to derepress the formation of the enzymes involved in thiamine biosynthesis, caused an increase in the rate of thiamine uptake in E. coli K12 as well as PT-R1 with a concomitant decrease in the cellular thiamine level. These results indicate that the formation of the thiamine transport system, probably of the “carrier” specific for thiamine in E. coli is controlled by repression and derepression.