Comparison of the metabolic fate and tissue distribution of B700, an albumin-like melanoma-specific antigen with serum albumin in normal and tumor-bearing mice.

1. B700, a murine melanoma antigen, is a member of the serum albumin protein family, being closely related to murine serum albumin (MSA). 2. We have studied and compared the metabolic fate and anatomic distribution of radioiodinated B700 and MSA administered to semisyngeneic naive and tumor-bearing mice. 3. Labelled material from both proteins is excreted primarily into urine. 4. The rate of excretion of the two proteins is markedly different, with B700 having a shorter half-life in the body. 5. Despite their similar molecular weights, intact B700 represents approx. 30% of the radioactivity in the urine but only 4% of the MSA in the urine is intact. 6. These studies demonstrate that the host can readily distinguish between very similar normal (MSA) and tumor-associated (B700) molecules and process them differently. 7. Similar findings of differential fate and distribution have been reported in comparing other albuminoid molecules [Dueland S., Blomhoff R. and Pedersen J. I. (1990) Biochem. J. 267, 721-725].