Substrate specificity for catalysis of phosphoryl transfer by the calcium ATPase of sarcoplasmic reticulum.

摘要: Abstract When α,β-methylene ADP (α,β-CH 2 -ADP) is added to the phosphorylated calcium ATPase of sarcoplasmic reticulum with Ca 2+ -bound, · E ∼ P Mg, ATP not synthesized (5 mM MgCl , 100 KCl, pH 7.0, 25°C). Similarly, adenosine 5′- O -(2-thiotriphosphate) from reaction phosphoenzyme -(2-thiodiphosphate), ADPβS. In contrast, formed rapidly and reversibly ADP. Both analogs are competitive inhibitors for binding K S = 0.45 mM: α,β-CH -ADP ADPβS bind 0.92 0.05 mM, respectively. We conclude that phosphoryl transfer kinetically blocked, although it thermodynamically favorable. The rate acceleration >10 5 Mg compared can be attributed differences in both structure net charge at 7.0. Phosphoryl so unfavorable we cannot determine whether transition state also unfavorable.