Sarcoplasmic reticulum calcium ATPase. Labeling of a putative Mg2+ site by reaction with a carbodiimide and a spin-label.
The sarcoplasmic reticulum Ca(2+)-ATPase loses hydrolytic activity and the ability to be phosphorylated by Pi following incubation with EDC [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide]. 4 nmol of tempamine per mg SR protein can be coupled to either a glu or an asp side chain through the EDC reaction. Mg2+ protects against loss of activity and tempamine labeling with a mid-point of about 3 mM in the absence of Ca2+. This is similar to the Kd for a Mg2+ that serves as a cofactor in enzyme phosphorylation. The Mg2+ protection constant is lowered by an order of magnitude when Ca2+ is bound to the transport sites. It is suggested that control of the Mg2+ binding site affinity may be part of the mechanism of enzyme activation by Ca2+.
Coan
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C
Department of Physiology, School of Dentistry, University of the Pacific, San Francisco, CA 94115.
Jakobs
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P
Ji
J Y
JY
Murphy
A J
AJ
D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003497:Cyclic N-Oxides / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005022:Ethyldimethylaminopropyl Carbodiimide / Q000378:metabolism* / Q000494:pharmacology; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D009132:Muscles / Q000201:enzymology*; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013113:Spin Labels
D003497:Cyclic N-Oxides; D005971:Glutamates; D013113:Spin Labels; C015527:4-amino-TEMPO; D001224:Aspartic Acid; D018698:Glutamic Acid; D004533:Egtazic Acid; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D005022:Ethyldimethylaminopropyl Carbodiimide; D002118:Calcium