ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Two protein kinase activities were found in plasma membrane-enriched preparations from red beet (Beta vulgarix L.). The kinases in these preparations produced the phosphorylation of several membrane polypeptides. These kinases also phosphorylated histone III-S and casein. The activities of two different kinases could be distinguished: one was half-maximally stimulated by 1 μM free Ca2+ phosphorylated histone III-S better than casein, showed half-maximal activity at an ATP concentration of 0.071 mM. had an optimum pH of 7, and was poorly inhibited by GTP, CTP or UTP. Another, much lower, kinase activity that phosphorylated casein was also observed; it was Ca2+ independent, showed half-maximal activity at ATP concentrations of 0.017 and 0.287 mM, exhibited a broad pH optimum about pH 7 and was inhibited by GTP, CTP, UTP or GDP to a greater extent than the calcium-stimulated activity. When plasma membrane proteins were solubilized with lysophosphatidyicholine and treated with [γ-32P]ATP at several dilutions, a 125-kDa polypeptide was autophosphorylated in the absence of Ca2+, while 77-, 71- and 65-kDa polypeptides were autophosphorylated in its presence. Autophosphorylation in gels after electrophoresis showed a Ca2+-stimulated phosphoprotein band at 64 kDa.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1994.tb00412.x
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