B700, a melanoma-specific antigen, catalyzes metabolism of prostaglandin E2

B700 is an albumin-like mouse-melanoma-specific antigen of unknown primary structure and biochemical function. The ability of mouse serum albumin to catalyze weak degradation of prostaglandin E2 has been utilized to compare functional similarities between B700 and mouse serum albumin. Both proteins catalyze the degradation of prostaglandin E2 to prostaglandin A2 and prostaglandin B2. This catalytic ability is related to the amino acid composition of the two proteins within the functional region rather than the 3-dimensional configuration, the activity is not altered upon boiling. The primary prostaglandin E2 metabolite in the presence of mouse serum albumin is prostaglandin B2, while prostaglandin A2 predominates in B700 catalyzed degradations. An additional product, presently unidentified, is produced during B700 catalyzed degradation of prostaglandin E2. Our studies indicate that the B700 protein has weak enzymatic activity for prostaglandin E2 similar to that of albumin. To our knowledge, B700 is the only melanoma antigen for which enzymatic activity has been demonstrated.