title: Properties of two isoforms of human blood platelet alpha-actinin.
abstract: The structural and functional properties of the aa (2 X 97 kDa) and cc (2 X 94 kDa) isoforms of platelet alpha-actinin have been compared. Structural differences between aa and cc are revealed by their peptide maps, obtained from limited proteolysis, and by their immunological cross-reactivity. Both isoforms stimulate the Mg ATPase activity of actomyosin, bind to F-actin (high-speed sedimentation) and cross-link or gel actin filaments (low-speed sedimentation and viscometry), in a calcium-dependent manner. The study of the interaction with F-actin indicates that the binding of 1 molecule of aa or cc alpha-actinin/9-11 actin monomers is sufficient to produce maximal gelation in the presence of EGTA. CaCl2 at 0.1 mM strongly inhibits the binding of aa to F-actin and weakly that of cc, while it inhibits similarly the cross-linking of either aa or cc. The cross-linking efficiency of cc is 9, 7, 1.7 and 1.3 times higher than that of aa at 4, 20, 30 and 37 degrees C, respectively. The bb form (2 X 96 kDa), which is a proteolytic product of aa [Y. Gache et al. (1984) Biochem. Biophys. Res. Commun. 124, 877-881], behaves roughly as aa, but the calcium sensitivity of its binding to F-actin is intermediate between that of aa and cc. These results suggest that the effect of Ca2+ concentration on the binding of platelet alpha-actinin to F-actin may be partly dissociated from the effect on the cross-linking.
mesh_terms: D000185:Actinin / Q000097:blood*; D000199:Actins / Q000097:blood; D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007536:Isomerism; D009132:Muscles / Q000378:metabolism; D010455:Peptides / Q000097:blood; D011817:Rabbits; D013696:Temperature; D014783:Viscosity
chemical_list: D000199:Actins; D010455:Peptides; D000185:Actinin; D000205:Actomyosin; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium