Vascular endothelial growth factor-A (VEGF-A) was originally isolated from tumor cells and referred to as Tumor Angiogenesis Factor or Vascular Permeability Factor. Although expressed at high levels in certain tumor-derived cells it is produced by a wide variety of cell types. In addition to stimulating vascular growth and vascular permeability, it may play a role in stimulating vasolidation via nitric oxide-dependent pathways. Alternative splicing of VEGF-A mRNA results in several isoforms of the protein. Rat and bovine VEGF are one amino acid shorter than the human factor, and the bovine and human sequences show a homology of 95 percent. In contrast to other factors mitogenic for endothelial cells such as FGF-1 , FGF-2 and PDGF, VEGF is synthesized as a precursor containing a typical hydrophobic secretory signal sequence of 26 amino acids. Glycosylation is not required for efficient secretion of VEGF. Recombinant Human VEGF-165 produced in E.Coli is a double, non-glycosylated, polypeptide chain containing 165 amino acids with a MW of 38231 Da.