title: A kinetic scheme for the early phase of ATP hydrolysis by actomyosin ATPase and its bioenergetic implications.
abstract: By following the absorption pattern of the dye orthocresol red in stopped flow spectrophotometer we have studied the H+ liberation in the early phase of ATP hydrolysis by myosin and actomyosin ATPases at different molar ratios of ATP:ATPase. In the case of myosin alone, we observe alkalination up to a molar ratio of 10:1 and net acidification above 30:1. In the case of actomyosin, hydrolysis results in acidification for all ratios. Estimation of Pi generated in the early phase, employing a coupled enzyme system, gives Pi early burst magnitude of 6.2/head of myosin. Interpreting alkalination as release of HPO2(4-) unaccompanied by H+ in the case of myosin for molar ratios less than 10:1 together with the results of Pi estimation we deduce that between 6 to 10, H+ ions are withheld by myosin in the early burst phase. Polymerized actin was found to induce concomitant release of H+ during the early phase of ATP hydrolysis. A kinetic scheme is proposed for actomyosin ATPase which encompasses the pre-steady state as well. Bioenergetic significance of these protons held by the myosin heads for the process of muscular contraction is discussed.
authors.affiliation: Centre for Biosciences, Jamia Millia Islamia, New Delhi, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Luqman
authors.forename: M
authors.initials: M
authors.lastname: Amin
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D004734:Energy Metabolism / Q000502:physiology*; D006868:Hydrolysis; D007700:Kinetics; D009218:Myosins / Q000378:metabolism*
chemical_list: D000255:Adenosine Triphosphate; D009218:Myosins