An abundant and novel protein of 22 kDa (SM22) is widely distributed in smooth muscles. Purification from bovine aorta.

Using a rabbit polyclonal-antibody preparation directed against the chicken gizzard protein, we demonstrated by immunoblotting the presence of the 22 kDa protein (SM22) in a variety of chicken smooth-muscle-containing organs, including uterus, intestine, gizzard, oesophagus and aorta. Protein SM22 was present in only trace amounts in brain, liver and heart, and could not be detected in chicken breast muscle. The antibody preparation did not cross-react with extracts of bovine aorta. However, the presence of SM22 as a major component in bovine aorta and pig carotid was demonstrated by its co-migration with the purified chicken gizzard protein on one- and two-dimensional polyacrylamide electrophoretic gels. Its molar abundance relative to actin was estimated to be 0.9:6.0 and 1.4:6.0 for bovine aorta and pig carotid respectively. Like the chicken gizzard protein, it separates on pH-gradient electrophoresis into at least three variants, alpha, beta and gamma, with similar apparent Mr. Purification of the aorta SM22 showed it to have a similar amino acid composition to the chicken gizzard protein. We conclude that SM22 is widely distributed and an abundant and unique protein component of smooth-muscle tissues of birds and mammals.