Lithium-7 nuclear magnetic resonance as a probe of structure and function of the monovalent cation site on pyruvate kinase

Pyruvate kinase: Activation by and catalytic role of the monovalent and divalent cations

“…Experiments using 7Li+ relaxation rates demonstrated that this weak activator also binds in the vicinity of the bound Mn +2 but 11 A away from Mn +2 (56) in contrast to the values of 8.3 + 0.3 A for TI + and CH3NH3~- (44,55). The addition of P-enolpyruvate to the enzymeMn+2-monovalent cation complex causes a dramatic increase in the effect of the bound Mn +2 on the relaxation rates of the monovalent cations (44,55,56). This effect is due to a decrease in the distance between the two cations at the catalytic site to 4.9 A for TI +, 6.3 A for CH~NH_3 + and 4.7 A for Li +.…”

A multinuclear nuclear magnetic resonance study of the monovalent-divalent cation sites of pyruvate kinase

“…only 3% as well as Tl+, these authors proposed that the longer metal-metal distance for the Li+ complexes compared with the Tl+ complexes correlated with the large decrease in enzymatic activity. Ash et al (1978) pointed out that there are two interconvertible forms of the enzyme-Mn2+-Li+-PEP complex (Reed & Cohn, 1973) that Hutton et al (1977) did not take account of in their data analysis. Repeating the 7Li NMR experiments, Ash et al (1978) obtained distances between Mn2+ and Li+ that are nearly identical with the Mn2+-Tl+ distances of Reuben & Kayne (1971).…”

Ion Binding in Biological Systems as Studied by NMR Spectroscopy

“…The 7Li+-Mn2+ distances obtained by Hutton et al (1977) in pyruvate kinase appear significantly different from the zo5T1+-Mn2+ distances obtained in the same enzyme (Reuben and Kayne, 1971), although the same value of 7c was used in the two cases. Since the ionic radius of Li+ (0.060 nm) is very much smaller than that of K+ (0.133 sec) (Grisham and Mildvan,19'74).…”

“…Both 7Li and gLi have very small nuclear quadrupole moments (see Section 11.4) and quadrupolar effects on their relaxation are weak. This fact renders it possible for other relaxation mechanisms to compete with quadrupolar relaxation, as is illustrated by two studies (Grisham and Hutton, 1978;Hutton et al, 1977). In the first work, 7Li NMR was used to probe the monovalent cation site on pyruvate kinase.…”

“…The enzyme also requires a divalent metal ion for full activity, for example, Mg2+ or the paramagnetic Mn2+. Hutton et al (1977) studied the 7Li+ NMR signal in 50mM LiCl solution. In the presence of about 2 -10-6M of the enzyme and Mg2+ in excess, no significant effect on the longitudinal relaxation of 7Li was observed.…”