Differential oligomerization of membrane-bound CD38/ADP-ribosyl cyclase in porcine heart microsomes.

A protein fraction displaying ADP-ribosyl cyclase activity was purified from porcine heart microsomes which appeared as a major band of 45 kDa on Coomassie blue stained SDS-PAGE gel under reducing condition. Protein immunoblot analysis with antiserum to recombinant rat CD38 showed a series of bands (45-285 kDa) under nonreducing condition, while only the 45 kDa monomer under reducing condition. The high molecular weight oligomers of CD38 were found to be stable even upon treatment with various concentrations of SDS in the sample buffer and also upon incubation at lower temperature. These oligomers of CD38 also displayed higher ADP-ribosyl cyclase activity than that of the monomer.