TYRPHOSTIN-47 NONENZYMATICALLY DECARBOXYLATES [1-C-14]-PYRUVATE

Tyrphostins inhibit tryosine kinases and have little effect on the act ivity of serine/threonine kinases. Pyruvate dehydrogenase kinase inact ivates pyruvate dehydrogenase by phosphorylating serine residues withi n the multienzyme complex. This serine/theronine kinase represents a n ew family of protein kinases, and one (tyrphostin 47) of two tyrphosti ns tested appeared to activate the pyruvate dehydrogenase kinase as de termined by [1-C-14]-lactate oxidation to (CO2)-C-14. Experiments desi gned to determine if the tyrphostins altered pyruvate dehydrogenase ac tivity in mitochondria prepared from rat epididymal adipocytes using [ 1-C-14]-pyruvate as the substrate demonstrated a dose dependent increa se in enzyme activity in the presence of tyrphostin 47, but not in tyr phostin 23. This apparent stimulation of pyruvate dehydrogenase activi ty was attributed to tyrphostin 47's ability to nonenzymatically decar boxylate [1-C-14]-pyruvate, the substrate for the pyruvate dehydrogena se assay. Neither tyrphostin directly altered pyruvate dehydrogenase k inase activity. Therefore, assays utilizing [1-C-14]-pyruvate and tyrp hostin 47 are subject to analytical interference.