An Adenosine 3',5'-Monophosphate-inhibited Protein Kinase from Physarum polycephalum

Glenn D Kuehn

doi:10.1016/s0021-9258(18)61800-9

Abstract

Abstract A potent protein kinase present in the acellular slime mold, Physarum polycephalum, which catalyzes the phosphorylation of casein by ATP has been found to be inhibited by cyclic adenosine 3', 5'-monophosphate (cAMP). The rate of the kinase-catalyzed phosphorylation of casein was completely inhibitable at a concentration of cAMP above 1 x 10-9 m. A cAMP-activated protein kinase, which is readily separable from the cAMP-inhibitable enzyme, is also present in this organism. The discovery of both of these enzymes in the same organism suggests a more complicated regulatory role for cAMP, via its effects on protein kinases, than previously proposed.

Highlights

A CAMP-activated protein kinase, which is readily separable from the CAMP-inhibitable enzyme, is present in this organism
The rate of the kinase-catalyzed phosphorylation of casein was completely inhibitable at a concentration of CAMP above 1 X 10Vg M
The initial discovery by Walsh, Perkins, and Krebs (l), in rabbit skeletal muscle, of a protein kinase that is activat,ed by CAMP’ provided impetus for extensive investigations into the distribution of this enzyme in various eukaryotic and prokaryotic cells [2,3,4,5,6,7,8,9,10,11,12]. Several of these enzymes have been purified and evidence of a common control mechanism explaining the interaction of CAMP with CAMP-activated protein kinases has recently been presented for enzymes isolated from rabbit skeletal muscle [13], beef heart, [14], and bovine adrenal cortex [15]

Summary

Carnitine Synthesis from Lysine

Even under these nutritional conditions, it is estimated that 0.074y0 of the administered DL-[6-14C]lysine was incorporated into “total liver and muscle carnitine” of Rat A (Fig. IA). This is a significant figure, part’icularly when it is considered that carnitine is presumably needed only at a catalytic level. Lysine deficiency in the rat has many features in common with starvation (lo), the end result classically being regarded as “protein malnutrition.” In this context the significance of the work reported may be in focusing on a previously unrecognized aspect of lysine deficiency, namely that leading to a diminution of carnitine synthesis in the tissues, a situation which could predictably result in adverse effects on fatty acid and energy metabolism as well

SUMMARY

Pmtein Kinase

Findings

DISCUSSION