ISSN:
1432-2048
Keywords:
Calcium and protein phosphorylation
;
Calmodulin
;
Cucurbita
;
Cyclic AMP
;
Protein phosphorylation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Protein-kinase activity has been found to be associated with a membrane fraction obtained from dark-grown zucchini (Cucurbita pepo L., cv. Senator) hypocotyl hooks. Proteins of this membrane fraction were used as protein substrates. The effects of Mg2+, Na+ and K+ on phosphorylation, measured as 32P incorporation, was investigated. The kinetics of phosphorylation of the individual protein peptides indicate the presence of specific phosphatase activity. Phosphorylation activity is strongly influenced by Ca2+. One peptide (relative molecular weight: 180,000) exhibits strong inhibition of 32P incorporation at physiological Ca2+ concentrations between 0.1 and 1 μM. Phosphorylation of about 10 other proteins was enhanced by Ca2+, being maximal in most cases at a concentration of about 3 μM free Ca2+. Five out of these 10 peptides show increased phosphorylation in the presence of 1 μM calmodulin. This calmodulin-dependent enhancement of phosphorylation could be completely inhibited by the calmodulin antagonist fluphenazine. Cyclic AMP was found to have no stimulating effect on protein phosphorylation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00397247
