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C J Pallen

Publications and source records attributed to C J Pallen.

41 records · Page 3Linked to original sources
PubMed1985

Demonstration of different metal ion-induced calcineurin conformations using a monoclonal antibody.

It has been suggested that calcineurin, a calmodulin-stimulated phosphatase, may exist in different metal ion-dependent conformational states (Pallen, C.J., and Wang, J. H. (1984) J. Biol. Chem. 259, 6134-6141). Evidence in favor of this hypothesis comes from studies involving a monoclonal antibody, VA1, which is specific for the small (beta) subunit of calcineurin. This antibody inhibits Ni2+-stimulated but not Mn2+-stimulated phosphatase activity against p-nitrophenyl phosphate and phosphorylase kinase. Inhibition is not due to competition of the antibody with substrate or to interference with metal ion binding to the enzyme. Complex formation between the antibody and calcineurin can be demonstrated either in the presence of Mn2+ or Ni2+ or in the absence of metal ion activators. These results indicate that the active conformational states of calcineurin are metal ion dependent, that the monoclonal antibody VA1 affects the Ni2+-induced conformational change of the enzyme, and that the beta subunit of calcineurin plays a critical role in the expression of Ni2+-stimulated phosphatase activity.

Animals↗
PubMed1985

A multifunctional calmodulin-stimulated phosphatase.

This review summarizes current knowledge concerning structure-function, substrate specificity, localization, and regulatory properties of calcineurin. Calcineurin is composed of two nonidentical subunits, one of which is responsible for catalytic activity and calmodulin binding while the other subunit contains four high-affinity Ca2+-binding sites. The enzyme possesses calmodulin-stimulated and metal ion-dependent phosphatase activity toward several nonprotein and phosphoseryl-, phosphothreonyl- and phosphotyrosyl-containing protein substrates. These recent results suggest that the protein may play a multifunctional role in interactions between the Ca2+/CaM second messenger system and other second messenger systems.

Animals↗
PubMed1984

Regulation of calcineurin by metal ions. Mechanism of activation by Ni2+ and an enhanced response to Ca2+/calmodulin.

Calcineurin possesses phosphatase activity towards both protein (Stewart, A.A., Ingebritsen , T.S., Manalan , A., Klee , C.B., and Cohen, P. (1982) FEBS Lett. 137, 80-84) and nonprotein substrates ( Pallen , C.J., and Wang, J.H. (1983) J. Biol. Chem. 258, 8550-8553). These phosphatase activities are divalent cation-dependent and stimulated by calmodulin. We have utilized the nonprotein chromogenic substrate p-nitrophenyl phosphate to investigate the effects of several divalent metal ions on calcineurin activity and have found that Ni2+ is the best activator of calcineurin both in the presence and absence of calmodulin. A slightly less potent activator is Mn2+. Although the mechanisms and extents of activation stimulated by these two metal ions are different, we present evidence to suggest a competition for binding to the enzyme. Pretreatment of calcineurin with either of these two metal ions enhances the activation of calcineurin by Ca2+/calmodulin and may be a physiological mechanism by which calcineurin activity is regulated by Ca2+.

Animals↗
PubMed1983

Calmodulin-stimulated dephosphorylation of p-nitrophenyl phosphate and free phosphotyrosine by calcineurin.

Calcineurin, a calmodulin-binding protein from brain, has been shown to possess a metal ion-dependent and calmodulin-stimulated phosphatase activity towards phosphorylase kinase and inhibitor-1 (Stewart, A. A., Ingebritsen, T. S., Manalan, A., Klee, C. B., and Cohen, P. (1982) FEBS Lett. 137, 80-84). In this report, we show that calcineurin can also dephosphorylate p-nitrophenyl phosphate and free phosphotyrosine. However, calcineurin does not show significant activity towards phosphothreonine, phosphoserine, or several other low molecular weight phosphocompounds tested. As we have found with phosphorylase kinase and phosphocasein, the dephosphorylation of p-nitrophenyl phosphate and free phosphotyrosine is stimulated by calmodulin and is metal ion-dependent with the order of efficiency being Mn2+ much greater than Co2+ greater than Ca2+. The dephosphorylation of these substrates appears to be an intrinsic property of calcineurin and is not due to contamination by alkaline phosphatases since the pH optimum for calcineurin activity occurs at a neutral rather than an alkaline pH. The dephosphorylation of p-nitrophenyl phosphate provides an easy, rapid, and accurate method for the quantification of calcineurin activity as well as permitting insight into reaction kinetics. The dephosphorylation of free phosphotyrosine by calcineurin suggests that this compound may be a physiological substrate of calcineurin.

Animals↗