Three forms of BRP-2 (bone resorptive proteins) from human cancer ascites fluid and their relationship to human serum alpha-2 HS-glycoprotein

Summary: Two new forms of BRP-2, a previously described bone resorptive protein, were purified from ascites fluids obtained from patients with hypercalcemia and metastatic bone cancer. The apparent molecular weights of BRP-2 and of these two proteins were 52,000, 48,000, and 46,000, respectively, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The three proteins have essentially the same amino acid compositions but differ with respect to their carbohydrate moieties. The amino-terminal amino acid sequences of the three glycoproteins were identical to each other as well as to human serum α₂HS-(human serum) glycoprotein. The relationship of the three forms of BRP-2 to α₂HS was also established immunochemically. The ascites proteins, as well as α₂HS, on a molar basis, were approximately one-tenth as potent as bovine parathyroid hormone fragment (1–34) in their abilities to stimulate calcium release from bonein vitro. This study describes for the first time a possible function for human serum α₂HS.