The isolation and activity of growth-stimulating factors from human platelets

Optimal conditions for determining the mitogenic activity of platelet growth factor in a homologous system (human palmar fascia fibroblasts/human platelet growth factor) were established. With the aid of this system it was possible to test the active fraction from crude platelet extract following affinity chromatography on heparin-Sepharose, chromatofocusing and molecular sieve filtration. This fraction has an isoelectric point of pH greater than 9 with a molecular mass of about 12000 daltons and reacts with beta-thromboglobulin antiserum. The addition of protease inhibitors proved essential for the isolation of the active growth factor, in order to prevent proteolytic degradation to a biologically inactive substance that is immunologically identical to beta-thromboglobulin. In addition to stimulation of DNA synthesis, the isolated growth factor induces enhanced synthesis of collagen and glycosaminoglycans in fibroblasts in vitro.