ATPase activity of requiem shark myosin.

Abstract

Effects of KCI, substrate and actin concentrations, along with pH, on ATPase activity of requiem shark myosin were examined.With increasing KCI concentration, the Ca2+-ATPase activity decreased almost linearly, while the K+ (EDTA)-ATPase activity increased significantly. The Ca2+-ATPase activity increased with increasing ATP concentration up to 0.6mM beyond which the activity remained at a roughly constant level. Kinetic constants, Km and Vmax were calculated to be 0.53mM and 0.40μmol Pi/min⋅mg, respectively. The myosin exhibited the highest K+ (EDTA)-ATPase activity at around 0.7mM ATP. The Km and Vmax calculated were 0.34mM and 0.27μmol Pi/min⋅mg, respecspectively.The Ca2+-ATPase of requiem shark myosin showed the pH optima at 6.5 and around 9.5, whereas the K+ (EDTA)-ATPase showed a single activity peak at around pH8.5. Actin significantly enhanced the Mg2+-ATPase activity of this myosin, the activity reaching a plateau at the actin to myosin weight ratio of 0.3-0.4.