Arginyl residue modification of the sarcoplasmic reticulum ATPase protein

Abstract

Reaction of rabbit sarcoplasmic reticulum vesicles with the arginyl residue reagent 2,3-butanedione results in the inactivation of the Ca +2-dependent ATPase activity. At pH 6.9, 25°, with 10 mM butanedione the pseudo-first order rate constant is 0.075 min −1. The kinetics approach zero order at 100 mM butanedione, suggesting that reversible binding of the reagent precedes the inactivation reaction. The presence of Mg-ATP strongly protects against inactivation. Similar but less effective protection is displayed by Mg-ADP and Ca-ATP, while Ca-acetyl phosphate or Mg +2 plus AMP or tripolyphosphate are ineffective. Measurement of the binding of [ 14C] ATP indicates that butanedione modification results in the complete loss of affinity for the substrate. These results suggest that one or more arginyl residues play a role in the substrate-active site interaction.