-Aminophenylboronic acid (APBA) inhibited the germination, growth and sporulation of NRRL B-2682 in an age- and concentration-dependent manner in submerged and solid cultures. When added to cells or cell extracts it irreversibly inhibited NAD-glycohydrolase and ADP-ribosyltransferase activity. ADP-ribosyltransferase was more sensitive, but inhibition was not complete, even in the presence of 10 mM APBA. The effects of the inhibitor correlated with its effect on ADP-ribosylation and on the profile of ADP-ribosylated endogenous proteins. The physiological importance of ADP-ribosyltransferase was supported by the observation that APBA strongly inhibited the growth of a non-sporulating and NAD-glycohydrolase-negative mutant of the parental strain. The resistance of NRRL B-2682 strains able to grow in the presence of APBA was due to permeability factors. A comparison of the ADP-ribosylated protein profiles of NRRL B-2682 grown under various conditions showed similarities, but also specific differences. The results suggest that the ADP-ribosyltransferase of NRRL B-2682 is an indispensable enzyme for growth and differentiation of the strain. It may regulate the activity of key enzymes or developmental proteins by responding to intra- and extracellular conditions.


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