In vitro enzyme activation with calbindin‐D28k, the vitamin D‐dependent 28 kDa calcium binding protein
- 3 February 1992
- journal article
- Published by Wiley in FEBS Letters
- Vol. 297 (1-2) , 127-131
- https://doi.org/10.1016/0014-5793(92)80342-e
Abstract
Purified porcine erythrocyte membrane Ca2+‐ATPase and 3′:5′‐cyclic nucleotide phosphodiesterase were stimulated in a dose‐dependent, saturable manner with the vitamin D‐dependent calcium binding protein from rat kidney, calbindin‐D28k (CaBP‐D28k). The concentration of CaBP‐D28k required for half‐maximal activation (K 0.5 act.) of the Ca2+‐ATPase was 28 nM compared to 2.2 nM for calmodulin (CaM), with maximal activation equivalent upon addition or either excess CaM or CaBP‐D28k, 3′:5′‐Cyclic nucleotide phosphodiesterase (PDE) also showed equivalent maximum saturable activation by calbindin (K 0.5 act. = 90 nM) or calmodulin (K 0.5 act. = 1.2 nM). CaBP‐D28k was shown to effectively compete with CaM‐Sepharose for PDE binding. Immunoprecipitation with CaBP‐D28k antiserum completely inhibited calbindin‐mediated activation of PDE but had no effect on calmodulin's ability to activate PDE. While the physiological significance of these results remains to be established, they do suggest that CaBP‐D28k can activate enzymes and may be a regulator of yet to be identified target enzymes in certain tissues.Keywords
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