Deuterium nuclear magnetic resonance study of the interaction of substrates and inhibitors with soybean lipoxygenase.

Deuterium NMR spectra for a series of selectively deuterated substrates and inhibitors in the presence of lipoxygenase-1 (EC 1.13.11.12) are presented. Extrapolation of the 2H NMR line widths yielded transverse relaxation rates for the bound inhibitors [2H21]dodecanoic acid (protonated at the 2,2-position), [2,2-2H]dodecanoic acid, and [12,12,12-2H]dodecanoic acid which are 1/T2,bd = 5.0 X 10(3), 1.12 X 10(4), and 1.16 X 10(3) s-1, respectively. The substrates [9,10,12,13-2H]linoleic acid and [11,11-2H]linoleic acid had 1/T2,bd = 8.2 X 10(3) and 7.95 X 10(3) s-1, respectively. Kinetic measurements established Ki = 1.5 X 10(-3) M for dodecanoic acid (lauric acid) inhibition of lipoxygenase when the substrate is linoleic acid (Km = 2.6 X 10(-5) M). Lipoxygenase, with Mr 102,000, is predicted to have a rotational correlation time tau c - 1.2 X 10(-7) s, yielding a 1/T2,bd = 1.56 X 10(4) s-1 for tightly bound ligand. Hence, the correlation times of the selectively deuterated inhibitors indicate internal motions are present in the bound species.