Actins from mammals, bird, fish and slime mold characterized by isoelectric focusing in polyacrylamide gels

Actins isolated from a variety of tissues and cultured cells were compared by isoelectric focusing in polyacrylamide gels in the presence of 9 M urea and 2% Nonidet P40. Actins isolated from muscle tissue with a sarcomeric structure like skeletal muscle and heart muscle invariably display, as previously shown, one single band with a pI of approximately 5.4 (alpha-actin) in isoelectric focusing gels. Actins isolated from mammalian or avian non-muscle tissue and cultured mammalian cells display two polypeptide bands (beta and gamma-actins) focusing at a slightly higher pH than alpha-actin as a closely spaced doublet. A gamma-like actin is the predominant species in chicken gizzard actin. However, this gamma-like form is not isoelectrically identical with gamma-actin from brain. These results are discussed in relation with the currently available amino acid sequence data known for different actins. Actin isolated from the liver of the electric fish Torpedo marmorata appears to consist of a single isoelectric species with an apparent isoelectric point similar to the beta-actin component of mammalian brain. The actin from the slime mold Physarum polycephalum shows only one single major band in isofocusing gels with an isoelectric point lower than that of alpha-actin.