L-Phenylalanine inhibition of muscle pyruvate kinase

The allosteric inhibition of M_l-type pyruvate kinase from rabbit skeletal muscle by phenylalanine is reciprocally dependent on Mg²⁺ and phosphoenolpyruvate concentrations. At pH 8, phenylalanine acts as a competitive inhibitor with respect to Mg²⁺ and phosphoenolpyruvate, and vice versa. Phenylalanine introduces sigmoidicity into the dependence of the reaction velocity on [Mg²⁺]. In vitro kinetic analysis indicates that phenylalanine inhibition of muscle pyruvate kinase is unlikely to have regulatory significance in vivo.