| Abstract: | Although adenine-requiring auxotrophs of Bacillus subtilis accumulate large quantities of inosine or hypoxanthine, or of both, they do not accumulate inosine-5'-monophosphate (IMP). Experiments directed at understanding this phenomenon were conducted with an adenineless auxotroph and with a mutant derived from it which lacked alkaline phosphohydrolase. It was found that B. subtilis contains four different phosphohydrolases. Only one is an extracellular enzyme; it is a 5'-nucleotide phosphohydrolase which can be inhibited by addition of CuSO(4) to the medium. Of the three cellular enzymes, only one, an acid phosphohydrolase, cannot attack 5'-nucleotides; this enzyme is not repressed by inorganic phosphate. One of the two remaining surface-bound enzymes is a nonspecific alkaline phosphohydrolase which attacks both 5'-nucleotides and p-nitrophenyl phosphate; this is the only phosphohydrolase that is markedly repressed by inorganic phosphate. The other surface-bound enzyme is a nonrepressible 5'-nucleotide phosphohydrolase with double pH optima: one at neutrality and the other near pH 9.0. The experiments indicate that the absence of IMP in the extracellular broth is due to degradation of internally accumulated IMP to inosine by the cellular 5'-nucleotide phosphohydrolase. |
