Acetyl phosphate as a substrate for the calcium ATPase of sarcoplasmic reticulum.
作者： A L Bodley , W P Jencks
DOI: 10.1016/S0021-9258(18)47894-5
关键词: Endoplasmic reticulum 、 Substrate (chemistry) 、 Calcium 、 Reaction rate constant 、 Steady state (chemistry) 、 Biophysics 、 Phosphorylation 、 Enzyme kinetics 、 Calcium ATPase 、 Chemistry 、 Cell biology 、 Biochemistry 、 Molecular biology
摘要: Acetyl phosphate is hydrolyzed by the calcium ATPase of leaky sarcoplasmic reticulum vesicles from rabbit skeletal muscle with Km = 6.5 mM and kcat 7.9 s-1 in presence 100 microM (180 K+, 5 MgSO4, pH 7.0, 25 degrees C). In absence calcium, hydrolysis 6% calcium-dependent rate at low 24% saturating concentrations acetyl phosphate. Values K0.5 for are 3.5 2.2 (n 1.6) 1 50 phosphate, respectively; inhibition follows 1.6 approximately 1.1) 0.5 1.3) 1.5 ATP. The phosphoenzyme formation consistent 43 kf 32 saturation; decomposition occurs kt 16 s-1. maximum fraction formed steady state 43-46%. These results kc congruent to 30 binding Ca2+ E [Ca2+], give cE.Ca2, activation Phosphoenzyme ATP shows same biphasic reaction ADP, constants that within experimental error, similar or identical It concluded pathways same, exception phosphorylation; an alternative, faster route avoids step available existence three different regions dependence on concentration turnover confirmed; high involves ATP-induced increase kt.
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