Are calcium-dependent protein kinases involved in the regulation of glycolytic/gluconeogenetic enzymes? Studies with XXXX /calmodulin-dependent protein kinase and protein kinase C.

@entity268 @entity948 @entity141 @entity95 @entity1391 @entity35 @entity2388
Changes in glycolytic flux have been observed in liver under conditions where effects of @entity268 seem unlikely. We have, therefore, studied the phosphorylation of four enzymes involved in the regulation of glycolysis and gluconeogenesis (6-phosphofructo-1-kinase from @entity35 liver and @entity95 muscle; @entity2388 kinase, 6-phosphofructo-2-kinase and @entity948 -1,6-bisphosphatase from @entity35 liver) by defined concentrations of two @entity268 -independent protein kinases: @entity141 /calmodulin-dependent protein kinase and @entity141 /phospholipid-dependent protein kinase (protein kinase C). The results were compared with those obtained with the catalytic subunit of @entity268 -dependent protein kinase. The following results were obtained. 1. @entity141 /calmodulin-dependent protein kinase phosphorylates 6-phosphofructo-1-kinase and L-type @entity2388 kinase at a slightly lower rate as compared to @entity268 -dependent protein kinase. 2. 6-Phosphofructo-1-kinase is phosphorylated by the two kinases at a single identical position. There is no additive phosphorylation. The final stoichiometry is 2 mol @entity1391 /mol tetramer. The same holds for L-type @entity2388 kinase except that the stoichiometry with either kinase or both kinases together is 4 mol @entity1391 /mol tetramer. 3. @entity95 muscle 6-phosphofructo-1-kinase is phosphorylated by @entity268 -dependent protein kinase but not by @entity141 /calmodulin-dependent protein kinase. 4. Fructose-1,6-bisphosphatase from @entity35 but not from @entity95 liver is phosphorylated at the same position but at a markedly lower rate by @entity141 /calmodulin-dependent protein kinase when compared to the phosphorylation by @entity268 -dependent protein kinase. 5. 6-Phosphofructo-2-kinase is phosphorylated by @entity141 /calmodulin-dependent protein kinase only at a negligible rate. 6. Protein kinase C does not seem to be involved in the regulation of the enzymes examined: only 6-phosphofructo-2-kinase became phosphorylated to a significant degree. In contrast to the phosphorylation by @entity268 -dependent protein kinase, this phosphorylation is not associated with a change of enzyme activity. This agrees with our observation that the sites of phosphorylation by the two kinases are different. The results indicate that @entity141 /calmodulin-dependent protein kinase but not protein kinase C could be involved in the regulation of hepatic glycolytic flux under conditions where changes in the activity of @entity268 -dependent protein kinase seem unlikely.
