Our previous studies indicated that IgE-mediated stimulation of rat baso- philic leukemia (RBL-2H3) cells resulted in the secretion of histamine and the phosphorylation of the heavy (200 kDa) and light (20 kDa) chains of myosin. In the case of the 20-kDa myosin light chain, all of the phosphate was confined to a single site, which could be identified as the serine residue phosphorylated by MLCK in both turkey gizzard smooth muscle and human platelet myosin. Following RBL-2H3 cell stimulation there was de novo phosphorylation of a serine site that had previously been shown to be phosphorylated by protein kinase C in turkey gizzard and human platelet myosin. A similar scenario was observed for the myosin heavy chain. Unstimulated cells contained myosin heavy chains that yielded a number of phosphorylate tryptic peptides. However, following antigen stimulation, a single new tryptic phosphopeptide appeared. This peptide appeared to be one whose phosphorylation was catalyzed by protein kinase C. The stoichiometry of phosphorylation of these sites was substantial (> 0.5 moles of phosphate/myosin, light and heavy chain) and was closely correlated with the extent of exocytosis.
Showing the most recent 10 out of 15 publications