excitation-contraction coupling
DESCRIPTION
Excitation-contraction coupling. Sliding filament mechanism independent studies by Huxley and Huxley (no relation) in 1954. Excitation-Contraction. contraction occurs when Ca 2+ binds with troponin C each cycle takes ~50 msec and sarcomere shortens ~10 nm - PowerPoint PPT PresentationTRANSCRIPT
Excitation-contraction Excitation-contraction couplingcoupling
Sliding filament mechanism• independent studies by Huxley and
Huxley (no relation) in 1954
Excitation-ContractionExcitation-Contraction
contraction occurs when contraction occurs when CaCa2+2+ binds with troponin C binds with troponin Ceach cycle takes ~50 msec each cycle takes ~50 msec and sarcomere shortens and sarcomere shortens ~10 nm~10 nmcontraction ceases when contraction ceases when CaCa2+2+ is removed from is removed from sarcoplasmsarcoplasm
ATP Hydrolysis: OverviewATP Hydrolysis: Overview
in resting state, ATP is partially hydrolyzedin resting state, ATP is partially hydrolyzedmyosin head binds to actin filament when binding myosin head binds to actin filament when binding becomes availablebecomes availableATP is completely hydrolyzed, and Pi and ADP ATP is completely hydrolyzed, and Pi and ADP are released from myosin headare released from myosin headactomyosin complex is broken when ATP binds actomyosin complex is broken when ATP binds to myosinto myosin
Maintenance of [ATP]Maintenance of [ATP] ii
myosin ATPasemyosin ATPase
ATP + HATP + H22O <O <—————> —————> ADP + Pi + H ADP + Pi + H++
creatine kinasecreatine kinase
PCr + ADP + HPCr + ADP + H++ < <—————> —————> Cr + ATP Cr + ATP
adenylate kinaseadenylate kinase
ADP + ADP <ADP + ADP <—————> —————> ATP + AMP ATP + AMP
ATP Hydrolysis: ATP Hydrolysis: WeakWeak Binding Phase Binding Phase
Transition 1Transition 1 – A-M binding; ATP enters myosin ATP pocket – A-M binding; ATP enters myosin ATP pocketTransition 2Transition 2 – ATP weakens A-M complex, myosin detaches – ATP weakens A-M complex, myosin detachesTransition 3Transition 3 – ATP partially hydrolyzed – ATP partially hydrolyzedTransition 4Transition 4 – myosin weakly reattaches to next actin molecule – myosin weakly reattaches to next actin molecule
ATP Hydrolysis: ATP Hydrolysis: StrongStrong Binding Phase Binding Phase
Transition 5Transition 5 – Pi released from myosin ATP pocket; myosin – Pi released from myosin ATP pocket; myosin cleft closes, strengthens bindingcleft closes, strengthens bindingTransition 6 Transition 6 – power stroke of myosin head– power stroke of myosin headTransition 7Transition 7 – ADP released (rate-limiting step) – ADP released (rate-limiting step)
Transition 1
Transition 2
Transition 3
Transition 5
Transitions 6-7Weak Binding
Strong Binding