Effects of Adenyl-5′-Imidodiphosphate and Vanadate Ion on the Intermolecular Cross-Linking of Ca2+-ATPase in the Sarcoplasmic Reticulum Membrane with N,N′-(l, 4-Phenylene)bismaleimide1

Abstract

The functional significance of the molecular interaction of Ca2(+)-ATPase in the sarcoplasmic reticulum (SR) membrane was examined using intermolecular cross-linking of Ca2(+)-ATPase with N,N'-(1,4-phenylene)bismaleimide (PBM). When SR vesicles were allowed to react with 1 mM PBM at pH 7 and 23 degrees C for various intervals and subjected to SDS-PAGE, the amount of the major band of monomeric ATPase decreased with a half life of about 20 min. Higher orders of oligomers were concurrently formed without accumulation of any particular species of oligomer. When SR vesicles were allowed to react with 1 mM PBM in the presence of 1 mM adenyl-5'-imidodiphosphate (AMP-PNP), the rate of oligomerization was markedly reduced and the amount of dimeric Ca2(+)-ATPase increased with time. After 1 h, more than 40% of the Ca2(+)-ATPase had accumulated in the dimeric form. When 1 mol of fluorescein isothiocyanate (FITC) was bound per mol of ATPase, the effects of AMP-PNP on the cross-linking with PBM were completely abolished. When SR vesicles were treated with PBM in the presence of 0.1 mM vanadate in Ca2+ free medium, the oligomerization of the Ca2(+)-ATPase by PBM was strongly inhibited. The vanadate effect on the cross-link formation was completely removed by the presence of Ca2+ and AMP-PNP in the reaction medium. When SR vesicles were pretreated with PBM in the presence of AMP-PNP and digested with trypsin for a short time, the dimeric ATPase was degraded to a peptide with an apparent molecular mass of about 170 kDa.(ABSTRACT TRUNCATED AT 250 WORDS)