Physiochemical characterization of ATP binding to human 5-lipoxygenase

Human 5-lipoxygenase requires ATP as a stimulatory factor. At the two preferred concentrations of the free Ca2+, 0.02 microM with a resting cell and 20 microM with a stimulated cell, Scatchard analysis revealed that 5-lipoxygenase has one affinity ATP binding site with a Kd of 4.6 microM at the low Ca2+ concentration but has two affinity ATP binding sites with a higher Kd of 4.4 microM and a lower Kd of 14.5 microM at the high Ca2+ concentration. In contrast, in a Tween 20 reaction system, 5-lipoxygenase had similar activation coefficients for ATP at both Ca2+ concentrations; these were 12.7 microM at the low Ca2+ concentration and 12.0 microM at the high Ca2+ concentration. These results showed that 5-lipoxygenase has an ATP binding site and suggest that self-association of 5-lipoxygenase in 20 microM Ca2+ may affect ATP binding affinity as measured by Scatchard analysis.