title: Effect of trypsin on rabbit skeletal muscle alpha-actinin.
abstract: 5 min of tryptic digestion of purified rabbit skeletal alpha-actinin decreases by approximately 75% the ability of alpha-actinin to cross-link F-actin filaments as measured viscometrically at 27 degrees C, but has little effect on the sedimentation coefficient of alpha actinin at 20 degrees C or an alpha-actinin's ability to increase the Mg2+-modified ATPase activity and rate of turbidity increase of reconstituted actomyosin suspensions. Twenty to sixty min of trypsin treatment reduces the sedimentation coefficient of alpha-actinin and destroys much of alpha-actinin's ability to increase the MG2+-modified ATPase and rate of turbidity increase of reconstituted actomyosin suspensions. Therefore, the ability of alpha-actinin to increase the rate of in vitro measures of muscle contraction may not result directly from alpha-actinin's ability to cross-link F-actin filaments. Trypsin does not split alpha-actinin into large fragments as it does myosin. Previous studies have shown that 35 to 65% of total tryptic-susceptible peptide bonds in alpha-actinin are split after 60 min of incubation with trypsin and that 30% of these bonds split in 60 min are cleaved during the first 5 min in a rapid reaction. That splitting of this group of peptide bonds has little effect on the sedimentation coefficient of alpha-actinin indicates that these bonds are located in a region of the alpha-actinin molecule where noncovalent forces are strong enough to maintain conformation of the native alpha-actinin molecule even after these bonds have been split. This ostensible segregation of alpha-actinin's ability to cross-link F-actin filaments from its ability to increase rate of in vitro assays of contraction by tryptic digestion may suggest that alpha-actinin could have at least two different physiological roles: (1) to bind actin filaments to each other or to basal structures, and (2) to enhance the effectiveness of actin in supporting movement.
mesh_terms: D000185:Actinin / Q000378:metabolism; D000205:Actomyosin; D000818:Animals; D004789:Enzyme Activation; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000201:enzymology; D010446:Peptide Fragments / Q000032:analysis; D011485:Protein Binding; D011817:Rabbits; D014357:Trypsin; D014783:Viscosity
chemical_list: D046911:Macromolecular Substances; D009124:Muscle Proteins; D010446:Peptide Fragments; D000185:Actinin; D000205:Actomyosin; D014357:Trypsin; D008274:Magnesium