title: Interaction of D-phenylalanine with Co(II)-substituted rabbit muscle pyruvate kinase: kinetic and optical properties.
abstract: The kinetic and optical properties of Co(II)-substituted pyruvate kinase in the presence of D-phenylalanine (D-Phe) were investigated. The results are discussed in comparison with the effects of its optical isomer L-phenylalanine (L-Phe) on the same enzyme. The catalytic effect of D-Phe on rabbit muscle pyruvate kinase depended upon the nature of the activating divalent metal ion used. It has stimulatory effect on Mg(II)-activated enzyme, but inhibitory effect on Co(II)-activated enzyme. Unlike the inhibitory effect of L-Phe, the inhibition of Co(II)-enzyme by D-Phe was not sensitive to the changes of pH and temperature, could not be reversed by L-alanine (L-Ala), displayed hyperbolic kinetics, and was noncompetitive with respect to phosphoenopyruvate saturation. D-Phe induced substantial visible circular dichroism (CD) spectral changes of Co(II)-enzyme similar to those induced by L-Phe. Although ultraviolet CD spectrum was not affected, D-Phe induced an ultraviolet difference absorption spectral change very similar to, but much smaller than, that induced by L-Phe. Our results support that D-Phe and other amino acids interact with the enzyme at two different sites: a common site, causing similar conformational changes which bear little direct kinetic relevance, and a kinetically relevant site, which is sterically dependent upon the side chain of the amino acids.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002942:Circular Dichroism; D003035:Cobalt / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D010649:Phenylalanine / Q000494:pharmacology*; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011817:Rabbits; D013056:Spectrophotometry, Ultraviolet
chemical_list: D003035:Cobalt; D010649:Phenylalanine; D011770:Pyruvate Kinase