THE ADIPSIN ACYLATION STIMULATING PROTEIN SYSTEM AND REGULATION OF INTRACELLULAR TRIGLYCERIDE SYNTHESIS

We have previously characterized an activity from human plasma that ma rkedly stimulates triglyceride synthesis in cultured human skin fibrob lasts and human adipocytes. Based on its in vitro activity we named th e active component acylation stimulating protein (ASP). The molecular identity of the active serum component has now been determined. NH2-te rminal sequence analysis, ion spray ionization mass spectroscopy, and amino acid composition analysis all indicate that the active purified protein is a fragment of the third component of plasma complement, C3a -desArg. As well, reconstitution experiments with complement factors B , D, and complement C3, the components necessary to generate C3a, have confirmed the identity of ASP as C3a. ASP appears to be the final eff ector molecule generated by a novel regulatory system that modulates t he rate of triglyceride synthesis in adipocytes.