Phosphorylation of Endogenous Membrane Proteins by Endogenous Protein Kinase at the Outer Surface of Ehrlich Cells

  • GUNNAR ÅGREN
  • GUNNAR RONQUIST

Abstract

An endogenous protein kinase at the surface of Ehrlich cells has been studied. Using exogenous (γ32P)ATP as a phosphoryl group donator, a transfer was demonstrated into endogenous acceptor protein(s) as well as to exogenous phosvitin. Seryl- and threonyl-residues isolated from the endogenous and exogenous acceptor protein were found to be labeled. The ratio between the labeled phosphorylserine and phosphorylthreonine was about 3.5:1 for both the endogenous acceptor of the intact cells and the exogenous acceptor. In similar experiments with a membrane preparation from Ehrlich cells, this ratio increased to about 7:1 provided the exogenous acceptor protein was absent. The results were independent of whether 1 × 10−5 M dibutyryl cyclic AMP was used or not with intact cells and a membrane fraction mainly consisting of vesicles. Whether the regulatory subunit of the membrane-associated protein kinase was in cis- or trans-disposition to the catalytic sub-unit no binding and dependence of the cyclic nucleotide was observed. Since the purified membrane fraction was considered free from endogenous cyclic AMP, it was concluded that the membrane-associated protein kinase of Ehrlich cells is not dependent on cyclic AMP. The critical role of arginine for the cyclic AMP dependence of the serine-containing residue in the catalytic subunit is discussed.

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Published
1976-09-01
How to Cite
ÅGREN G., & RONQUIST G. (1976). Phosphorylation of Endogenous Membrane Proteins by Endogenous Protein Kinase at the Outer Surface of Ehrlich Cells. Upsala Journal of Medical Sciences, 81(3), 129-134. https://doi.org/10.3109/03009737609179035
Section
Original Articles

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