Protein phosphorylation in vitro in brain tubulin preparations: effects of Zn2+ and cyclic nucleotides

Larsson, H.; Edström, A.; Wallin, M.

Journal of Neurochemistry 29(1): 115-120

1977


ISSN/ISBN: 0022-3042
PMID: 196041
DOI: 10.1111/j.1471-4159.1977.tb03932.x
Accession: 068523651

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Abstract
Endogenous protein phosphorylation was studied during in vitro polymerization of microtubules by incubating a purified tubulin preparation at 37.degree. C in the presence of radioactive ATP. At optimal conditions the rate of phosphorylation followed the course of polymerization by a shift to a lower rate at the polymerization plateau. Zn2+ (0.5 mM) stimulated phosphorylation, mainly of tubulin-associated proteins MW 110,000 and 175,000), and to a lesser extent of tubulin. The effect occurred at Zn2+ concentrations which induced formation of tubulin sheet polymers, which suggested that the state of aggregation of tubulin is of importance for the phosphorylation. In contrast to Zn2+, Mg2+ only increased phosphorylation of the high MW proteins, and to a lesser degree. The stimulation by Zn2+ or Mg2+ was potentiated by cyclic (c)AMP or cGMP. A low concentration of Zn2+ (5 .mu.M) or cGMP at 10 .mu.M inhibited phosphorylation, possibly by interaction with a co-existing protein phosphatase.