标题：Stimulation of phosphorylation of lipocortin at threonine residues by epidermal growth factor (EGF) and the EGF receptor: addition of protein kinase P with polylysine inhibits this effect
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1989
卷号：86
期号：16
页码：6072-6076
DOI：10.1073/pnas.86.16.6072
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：In this paper we show that epidermal growth factor (EGF) stimulates the phosphorylation of lipocortin 1, at threonine as well as at tyrosine residues, by a highly purified preparation of the EGF receptor. The phosphorylation of threonine residues is catalyzed by an enzyme that contaminates the receptor preparations, since crude extracts of A431 plasma membranes contain larger amounts of the threonine kinase than does the receptor preparation. Protein kinase P (2.5 ng) inhibits both threonine and tyrosine phosphorylation of lipocortin 1 while greatly stimulating the autophosphorylation of the EGF receptor. Acetyllipocortin 1 is poorly phosphorylated at tyrosine residues by the EGF receptor kinase, but it becomes readily phosphorylated in the presence of polylysine. The most likely explanation for this observation is that there is an interaction between polylysine and acetyllipocortin that converts the latter into a suitable substrate for the EGF receptor. These and other experiments described in this paper point to a role of surface charges in the susceptibility of substrates to attach by protein kinases.
