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J P Andersen

Publications and source records attributed to J P Andersen.

77 records · Page 5Linked to original sources
PubMed1980

Properties of detergent-solubilized and membranous (Ca2+ + Mg2+)-activated ATPase from sarcoplasmic reticulum as studied by sulfhydryl reactivity and ESR spectroscopy. Effect of protein-protein interactions.

(1) Sulfhydryl reactivity and electron spin resonance spectra of nitroxide maleimide spin labels, covalently attached to sarcoplasmic reticulum ATPase, were examined on both detergent-solubilized and membranous material. Monomeric and oligomeric ATPases were prepared by the use of dodecyloctaethylene glycol monoether as a solubilizing detergent. (2) Immediately after solubilization, the reaction curve of nonomeric ATPase with 5,5'-dithiobis(2-nitrobenzoate) was characterized by positive cooperativity (S-shaped as a function of time). In contrast, the SH reactivity of both oligomeric and membranous ATPases obeyed usual first-order kinetics and could be analyzed in terms of three classes of reactive site. All enzymatically active ATPase preparations responded to addition of ADP with a decrease in SH reactivity. During enzymatic inactivation of monomeric ATPase, the SH-modification rate was dramatically enhanced with loss of cooperative features. Ca2+ removal from the high-affinity sites stimulated SH reactivity before inactivation had taken place. (3) ESR spectroscopy indicated less motional constraints on monomeric than on oligomeric and membranous ATPases. Arrhenius plots of ESR spectral parameters suggest a conformational transition in both membranous and solubilized ATPases at about 22 degrees C. The transition was also present in EGTA-, but not in heat-inactivated ATPase. Although SH reactivity of monomeric ATPase was dramatically enhanced by EGTA inactivation, the results of ESR, circular dichroism and analytical ultracentrifugation experiments indicate limited conformational changes induced by EGTA treatment. (4) The data indicate marked differences in the properties of monomeric ATPase on the one hand and oligomeric and membranous enzymes on the other hand. They are consistent with previous functional evidence for the presence of ATPase in an associated state in the membrane (Møller, J.V., Lind, K.E. and Andersen, J.P. (1980) J. Biol. Chem. 255, 1912-1920).

Animals↗
PubMedDate not supplied

Functional significance of quaternary organization of the sarcoplasmic reticulum Ca2+-ATPase.

There is both structural and functional evidence for protein-protein interaction between Ca2+-ATPase polypeptide chains in the sarcoplasmic reticulum membrane. Studies on detergent solubilized ATPase indicate that the monomeric form is capable of performing a normal cycle of ATP hydrolysis, but some of the modulatory effects of the substrates disappear after detergent solubilization. However, the necessity of protein-protein interactions for the Ca2+ transport function remains unclarified. A new approach is described, employing ATPase reconstituted with a large excess of phospholipid, which may help to resolve this question.

Adenosine Triphosphate↗