Abstract
A mutant strain of Escherichia coil 64-21, requiring either high concentrations of hydroxymethylpyrimidine or low concentrations of thiamine, has been produced from mutant 26-43 which requires the thiazole moiety of thiamine. The concentration of hydroxymethyl-pyrimidine required for a half maximal growth of mutant 64-21 was approximately 10, 000 times higher than that of thiamine. Mutant 26-43 cells were able to take up hydroxymethylpyrimidine and then utilized it as a precursor for thiamine biosynthesis, whereas mutant 64-21 cells could not take up hydroxymethylpyrimidine in a significant amount when it was supplied at 0.01mM. Increasing concentrations of external hydroxy-methylpyrimidine resulted in increasing the amount of intracellular hydroxymethylpyrimidine compounds but the amounts proved to be always far less than the amounts taken up by mutant 26-43 cells. In addition, phosphomethylpyrimidine kinase activity was deficient in this organism and the reaction did not proceed unless a high concentration of hydroxymethylpyrimidine monophosphate was added. Another mutant, 70-23, requiring thiamine in an intact form, lacked phospho-methylpyrimidine kinase activity and also proved to be lacking in the ability to take up hydroxymethylpyrimidine. These results lead to the conclusion that phosphomethylpyrimidine kinase might participate in the passage of hydroxymethylpyrimidine through the cell membrane and the enzyme in mutant 64-21 could not catalyze the reaction from hydroxy-methylpyrimidine monophosphate to the pyrophosphate unless a high concentration of hydroxymethylpyrimidine, hence, hydroxymethylpyri-midine monophosphate, was available intracellularly.
