A novel myosin heavy chain isoform in vascular smooth muscle.

Previous studies demonstrated two myosin heavy chain isoforms in vascular smooth muscles with SDS-polyacrylamide gel electrophoresis; MHC1 (204 kDa) and MHC2 (200 kDa). We report the existence of a novel myosin heavy chain isoform, MHC3 (196 kDa), which was exclusively contained in inferior vena cava. Equal amount of MHC1 and MHC2 was observed in aorta and pulmonary artery, respectively. However, inferior vena cava contained only MHC3. Proteolytic artifact was refuted by immunoblotting of tissue homogenates without purification, or SDS-polyacrylamide gel electrophoresis of myosin bands isolated by pyrophosphate gel electrophoresis. Furthermore, alpha-chymotryptic cleavage of MHC1, MHC2, and MHC3 displayed different peptide maps, indicating the primary structural difference among all three isoforms.