NAD turnover in microplasmodia of physarum polycephalum.

The rate of NAD turnover in microplasmodia of Physarum polycephalum was investigated using a double labeling technique with (14C)-adenine or adenosine and (3H)-nicotinamide. The half-life of an NAD molecule in Physarum was estimated to be 25 min, which is shorter than in either E. coli or human cell lines. The half-life of NAD in the presence of an inhibitor of NADase and poly ADPR synthase, 5-methylnicotinamide, was also investigated, but found to be indistinguishable from controls. The possible reasons for this and for the rapid turnover is discussed in the light of the known functions for NAD in prokaryotes and eukaryotes.