. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 188 FUTURE OF AQUATIC RESEARCH IN SPACE Actin Myosin ATP Strong- binding states ADP \ Weak- binding states ADP. Power stroke Figure 2. ATP hydrolysis by myosin. In the absence of bound nucleotide, myosin is bound tightly to actin. The consequence of ATP binding is a dramatic decrease in the affinity of myosin for actin: the complex then enters several so-called "weak-binding ; in which myosin only transiently interacts with actin. ATP is hydrolyzed to ADP and P, in a readily reversible step, then P, is relea
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 188 FUTURE OF AQUATIC RESEARCH IN SPACE Actin Myosin ATP Strong- binding states ADP \ Weak- binding states ADP. Power stroke Figure 2. ATP hydrolysis by myosin. In the absence of bound nucleotide, myosin is bound tightly to actin. The consequence of ATP binding is a dramatic decrease in the affinity of myosin for actin: the complex then enters several so-called "weak-binding ; in which myosin only transiently interacts with actin. ATP is hydrolyzed to ADP and P, in a readily reversible step, then P, is released and myosin rehinds actin. Following P, release, a kinetically irreversible step is surmounted, which is probably associ- ated with the power stroke that generates forces and displaces actin and myosin filaments. When ADP is bound, like the subsequent nucleotide-free state, myosin is bound tightly to actin. The effect of adenine nucleotide diphosphates like ADP and ADP/i should be to lock the myosin in a tightly bound complex with actin; adaptation motors would therefore be unable to release from actin or carry out power strokes. By contrast, phosphate analogs like vanadate. beryllium fluoride, and sulfate should increase the popula- tion of weakly bound states, decreasing force production and inhibiting climbing b\ the adaptation motors. proach that relies on the properties of myosirTs ATPase cycle. In this method, purified hair bundles (Gillespie and Hudspeth, 1991) are incubated with a radioactive nucleotide, such as [«-32P]UTP, and a trapping phos- phate analog, such as vanadate. After the nucleotide is hydrolyzed and P, is released, vanadate binds to myosin and traps the nucleotide in a slowly dissociating state. Thorough washing eliminates nucleotides bound to other bundle proteins, then radioactive nucleotides are covalently crosslinked to myosin molecules by UV irra- diation. We found that three myosin isozymes, of 120, 160, and 230 kD, were most consistently labele
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
