VEGF is a heavily glycosylated, homodimeric protein. The human factor occurs in several molecular variants of 121, 162, 145, 148, 165, 183, 189, 206 amino acids, arising by alternative splicing of the mRNA. The splice forms of VEGF differ in biological properties such as the receptor types, which they recognize and their interaction with heparan sulfate proteoglycans. VEGF121 and VEGF165 are soluble secreted forms of the factor. The interaction of VEGF with heparin-like molecules of the extracellular matrix is required for efficient receptor binding. Protamine sulfate and suramin are capable of replacing the receptor-bound factor. This recombinant construct represents the isoform 121 of VEGFA.