Structural and biological characteristics of connective tissue activating peptide (CTAP-III), a major human platelet-derived growth factor.

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Abstract
Connective tissue activating peptides (CTAP) extracted from leukocytes and platelets stimulate glycolysis and synthesis of glycosaminoglycan and DNA in cultured human connective tissue cells. CTAP-III, isolated from fresh or outdated human platelets, is a low MW single-chain protein with an isoelectric point of 8.5 that markedly stimulates DNA synthesis and multiple aspects of glycosaminoglycan and proteoglycan metabolism. A definitive comparison was made of CTAP-III prepared by 2 methods [one designated (A), alternative] with similar platelet proteins described by others, .beta.-thromboglobulin (.beta.-TG) and low-affinity platelet factor 4(LA-PF-4). CTAP-III, CTAP-III(A), LA-PF-4 and .beta.-TG have common antigenic determinants documented by immunoprecipitation and radioimmunoassay. CTAP-III, CTAP-III(A) and LA-PF-4 are biologically active in that they stimulate DNA and glycosaminoglycan synthesis by human synovial cells; .beta.-TG is inactive. Carboxyl-terminal digestion gave identical terminal sequences for CTAP-III, CTAP-III(A) and .beta.-TG. Amino-terminal sequence data indicate that CTAP-III and CTAP-III(A) (also LA-PF-4) are identical and differ from .beta.-TG only by an additional amino-terminal tetrapeptide (Asn-Leu-Ala-Lys-). The biologically active molecule, CTAP-III, may be proteolytically converted to its inactive degradation product (.beta.-TG) in the course of platelet aging, platelet storage, release from the platelets or initiation of biological activity.