Inhibition of chicken pyruvate kinases by amino acids

Abstract

Alanine, serine, and phenylalanine behave as inhibitors competitive with phosphoenolpyruvate for the activated forms of the chicken pyruvate kinases. On the other hand, phenylalanine and alanine behave as K-type inhibitors and serine behaves as a heterotropic activator of pyruvate kinase variants which undergo homotropic activation. Tryptophan lowers the Vm and tends to yield complex plots with all variants studied. Kinetic patterns obtained in the presence of phenylalanine also show some characteristics not generally associated with a competitive mechanism. These observations are related to data previously obtained using the rat isozymes and are used to formulate a mechanism which explains the effects of the amino acids. This mechanism hypothesizes that all the effector amino acids bind to the phosphoenolpyruvate site; however, amino acids with nonpolar side chains also interact with a nonpolar region of the T conformer and thereby stabilize it. It is further proposed that there are two such nonpolar regions on the various pyruvate kinases--the one which reacts with the nonbulky side chains, and another which reacts only with relatively bulky side chains. The stabilizing effect of this second nonpolar interaction imparts inhibitory characteristics which are not competitive in nature. Serine and perhaps other polar compounds may also bind at the phosphoenolpyruvate site, but because of their polarity exert a repulsive force at the same nonpolar site with which the nonbulky nonpolar amino acids interact. This repulsion stabilizes the R conformation. Presumably the homotropic activating effects of phosphoenolpyruvate operate via this same mechanism. The data are also used to support a specific sequential-concerted mechanism for the homotropic activating effect of phosphoenolpyruvate. According to this mechanism, phosphoenolpyruvate adds sequentially to the first two subunits. This interaction causes the respective subunits to convert to the R conformation but, once two subunits are in R conformation, the remaining two subunits convert in concert.

Small Molecule Activation of PKM2 in Cancer Cells Induces Serine Auxotrophy

“…In contrast, 9 was impervious to inhibition by phosphopeptides (Figure 2B). PKM2 has also been reported to be inhibited by the amino acids alanine and phenylalanine but activated by serine (Ibsen and Marles, 1976). In fact, the M2 isoform was once defined in part by its sensitivity to inhibition by alanine, in contrast to the M1 isoform (van Veelen et al, 1977).…”

PKM2, a Central Point of Regulation in Cancer Metabolism

“…Whether this interaction contributed to TEM8-Fc-associated tumor suppression was not clear [92]. Consistent with the knowledge that PKM2 plays a critical role in regulating aerobic glycolysis and biosynthesis for cellular building blocks, PKM2 is activated by serine but inhibited by alanine and phenylalanine when bound to these amino acids [93]. …”

Pyruvate kinase: Function, regulation and role in cancer

“…Consistent with the ability of FBP to stabilize PKM2 tetramers, alanine inhibition can be fully overcome by FBP [66, 67]. Serine binds in the same pocket as alanine and phenylalanine, but serine acts as an allosteric activator of PKM2 [17, 68] with a reported AC 50 of 1.3 mM [69]. Serine and alanine compete with phenylalanine for binding to PKM1 [63], but the effect of combinations of these allosteric effectors on PKM2 has not been explored.…”