ACTIN FROM EMBRYONIC CHICK BRAIN - ISOLATION IN HIGH-YIELD AND COMPARISON OF BIOCHEMICAL-PROPERTIES WITH CHICKEN MUSCLE ACTIN

Actin has beon isolated from chick embryo brain by a method which results in a 76% recovery of total brain actin with >98% purity as evidenced by densitometry of NaDodSO4-containing acrylamide gels. The isolated brain actin demonstrates the same critical actin concentration for assembly as does skeletal muscle actin when assembly is initiated with 4 mM MgCl2 and 0.1 M KCl. Under these conditions, the rates and extents of brain and muscle actin assembly are identical as followed by viscometry and by absorbancy changes at 232 nm. Similarity in conformation of the brain and muscle G-actins has also been demonstrated by spectropolarimetry in the 260-195-nm region. Biochemical characterization of the isolated chick brain actin and comparison with purified chicken and rabbit skeletal muscle actins indicate that, although the proteins are related, brain contains distinctly unique actin species. Muscle actin generated the α isoelectric focusing species and brain actin the β and γ species previously observed for muscle and nonmuscle actins, respectively. Amino acid analysis shows chick brain actin contains more Gly and slightly less Asp, Tyr, and Met than does chicken muscle actin. Both actins contain identical composition of the remaining amino acids including one residue of 3-methyl-l-histidine. Both brain and muscle actin also contain 1 mol of Ca2+/mol as determined by atomic absorption analysis. Brain actin contained at least one cyanogen bromide peptide not found in chicken muscle actin while the muscle actin contained at least three unique cyanogen bromide peptides. © 1979, American Chemical Society. All rights reserved.