{"title":"Functional approach to the catalytic site of the sarcoplasmic reticulum Ca(2+)-ATPase: binding and hydrolysis of ATP in the absence of Ca(2+)","authors":"A Lax, F Soler, F Fernandez Belda","doi":"arxiv-2401.17382","DOIUrl":null,"url":null,"abstract":"Isolated sarcoplasmic reticulum vesicles in the presence of Mg(2+) and\nabsence of Ca(2+) retain significant ATP hydrolytic activity that can be\nattributed to the Ca(2+)-ATPase protein. At neutral pH and the presence of 5 mM\nMg(2+), the dependence of the hydrolysis rate on a linear ATP concentration\nscale can be fitted by a single hyperbolic function. MgATP hydrolysis is\ninhibited by either free Mg(2+) or free ATP. The rate of ATP hydrolysis is not\nperturbed by vanadate, whereas the rate of p-nitrophenyl phosphate hydrolysis\nis not altered by a nonhydrolyzable ATP analog. ATP binding affinity at neutral\npH and in a Ca(2+)-free medium is increased by Mg(2+) but decreased by vanadate\nwhen Mg(2+) is present. It is suggested that MgATP hydrolysis in the absence of\nCa(2+) requires some optimal adjustment of the enzyme cytoplasmic domains. The\nCa(2+)-independent activity is operative at basal levels of cytoplasmic Ca(2+)\nor when the Ca(2+) binding transition is impeded.","PeriodicalId":501325,"journal":{"name":"arXiv - QuanBio - Molecular Networks","volume":"22 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - QuanBio - Molecular Networks","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2401.17382","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Isolated sarcoplasmic reticulum vesicles in the presence of Mg(2+) and
absence of Ca(2+) retain significant ATP hydrolytic activity that can be
attributed to the Ca(2+)-ATPase protein. At neutral pH and the presence of 5 mM
Mg(2+), the dependence of the hydrolysis rate on a linear ATP concentration
scale can be fitted by a single hyperbolic function. MgATP hydrolysis is
inhibited by either free Mg(2+) or free ATP. The rate of ATP hydrolysis is not
perturbed by vanadate, whereas the rate of p-nitrophenyl phosphate hydrolysis
is not altered by a nonhydrolyzable ATP analog. ATP binding affinity at neutral
pH and in a Ca(2+)-free medium is increased by Mg(2+) but decreased by vanadate
when Mg(2+) is present. It is suggested that MgATP hydrolysis in the absence of
Ca(2+) requires some optimal adjustment of the enzyme cytoplasmic domains. The
Ca(2+)-independent activity is operative at basal levels of cytoplasmic Ca(2+)
or when the Ca(2+) binding transition is impeded.