A disulfide-linked heterodimeric protein complex comprised of one platelet-derived growth factor subunit A and one platelet-derived growth factor subunit B. This dimeric growth factor binds to a heterodimeric receptor comprised of one platelet-derived growth factor receptor alpha and one platelet-derived growth factor receptor beta. Ligand binding activates the intrinsic tyrosine-protein kinase activity of the receptor complex and initiates signal transduction pathways. [ ]