Substrate regulation of calcium binding in Ca2+-ATPase molecules of the sarcoplasmic reticulum: II. Effect of CTP, GTP, ITP, and UTP

Jun Nakamura, Genichi Tajima, Chikara Sato

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2 Citations (Scopus)

Abstract

To examine the effect of CTP, GTP, ITP, and UTP on calcium binding of Ca2+-ATPase molecules of the sarcoplasmic reticulum, the calcium dependence of the Ca2+activated hydrolysis activities of these NTPs of the enzyme molecules was examined by comparison with that of calcium binding of the molecules in the absence of the NTPs at pH 7.40. In the sarcoplasmic reticulum membrane, CTP, GTP, and ITP did not affect the noncooperative (Hill value (nH) of ∼ 1, apparent calcium affinity (K0.5) of 2-6 μM)) and cooperative (nH ∼ 2, K0.5 ∼ 0.2 μM) calcium binding of the molecules, whereas UTP caused the molecules to highly cooperatively (nH ∼ 4) bind calcium ions with a lowered K0.5 of ∼ 0.04 μM. When the enzyme molecules were solubilized with detergent, all of these NTPs reversibly degraded the calcium affinity of the molecule (from K0.5 = 3-5 to >40 μM), although the effect of the NTPs on the negatively cooperative manner (nH ∼ 0.5) of calcium binding was not experimentally obtained. Taking into account the first part of this study (Nakamura, J., Tajima, G., Sato, C., Furukohri, T., and Konishi, K. (2002) J. Biol. Chem. 277, 24180-24190) showing the improving effect of ATP on calcium binding of the membranous and solubilized molecules, the results show that ATP is the only intrinsic substrate for the enzyme molecule. This NTP regulation is discussed in terms of the oligomeric structure of the molecules.

Original languageEnglish
Pages (from-to)24191-24196
Number of pages6
JournalJournal of Biological Chemistry
Volume277
Issue number27
DOIs
Publication statusPublished - 2002 Jul 5

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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