Structure, function, and regulation of amidophosphoribosyltransferase from prokaryotes

Recent studies on the structure, function and regulation of amidophosphoribosyltransferase from E. coli and B. subtilis are reviewed and these properties compared with those of the enzyme from eukaryotes. The availability of large amounts of stable enzyme from the two microbial sources has facilitated the recent studies. The enzyme subunits from E. coli and B. subtilis are of similar size, 56, 395 and approximately 50,000, respectively. Catalytic properties and patterns for allosteric inhibition are similar but not identical. There are two major differences between these enzymes. In contrast to the enzyme from E. coli, B. subtilis amidophosphoribosyltransferase contains an essential Fe-S center. In addition, the enzyme from B. subtilis but not E. coli is inactivated in stationary phase by an oxygen-dependent mechanism which appears to have regulatory significance. As a consequence of the Fe-S center B. subtilis amidophosphoribosyltransferase is oxygen-sensitive in vitro. Amidophosphoribosyltransferase from mammalian sources is similar to the B. subtilis enzyme in its oxygen-sensitivity which may result from an Fe-S center. The amino acid sequence of E. coli amidophosphoribosyltransferase was deduced from the DNA sequence of the purF structural gene. The primary translation product contains 504 amino acid residues. Met-1 is removed by processing leaving an NH2-terminal cysteine residue. The NH2-terminal cysteine was specifically alkylated by the glutamine affinity analog 6-diazo-5-oxonorleucine and is thus identified as the cysteine residue involved in formation of the glutaminyl-enzyme covalent intermediate. The mechanism for glutamine utilization appears identical to other glutamine amido-transferases. Sequence homology was not detected in the glutamine amide transfer domains of E. coli anthranilate synthase and amidophosphoribosyltransferase.