SEQUENTIAL BLOCKADE IN ADENINE BIOSYNTHESIS BY GENETIC LOSS OF AN APPARENT BIFUNCTIONAL DEACYLASE

Abstract
Some adenine-requiring mutants of Escherichia coli and Salmonella typhimurium accumulate a precursor which has been identified as the ribotide of 5-amino-4-imidazole-N-succinylocarboxamide (S-AICAR). The riboside was also found. The accumulation is due to a mutational loss of a deacylating enzyme, which splits S-AICAR to yield the ribotide of 5-amino-4-imidazolecarboxyamide. This loss is accompanied by a loss of the ability to deacylate adenylo-succinic to adenylic acid, resulting in the specific requirement for adenine. Thus, the mutational loss of this apparent bifunctional deacylase creates a double block along the biosynthetlc pathway to nucleic acid adenine.