Occurrence of bovine spleen CD38/NAD+glycohydrolase disulfide-linked dimers

Bovine spleen NAD+glycohydrolase, an ecto-enzyme closely related to CD38, catalyzes the conversion of NAD+ into ADP-ribose and cyclic ADP-ribose, a calcium-mobilizing metabolite. We have raised polyclonal antibodies against the native enzyme which on immunoblots revealed, besides the 32 kDa monomer, the presence of a stable dimeric form. This dimerization was shown to result from a spontaneous oxidative process involving the formation of one or several disulfide bond(s) sensitive to reducing agents such as 2-mercaptoethanol. The homodimeric oxidized enzyme, which was not detected during the early steps of the enzyme purification procedure, was catalytically active. Our results underline the differences, in terms of oligomerization and reactivity towards thiols, between CD38/NAD+glycohydrolases depending on their origin.