PHYSICOCHEMICAL 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 mu M with a resting ce ll and 20 mu M With a stimulated cell, Scatchard analysis revealed tha t 5-lipoxygenase has one affinity ATP binding site with a K-d of 4.6 m u M at the low Ca2+ concentration but has two affinity ATP binding sit es with a higher K-d of 4.4 mu M and a lower K-d of 14.5 mu M at the h igh Ca2+ concentration. In contrast, in a Tween 20 reaction system, 5- lipoxygenase had similar activation coefficients for ATP at both Ca2concentrations; these were 12.7 mu M at the low Ca2+ concentration and 12.0 mu M at the high Ca2+ concentration. These results showed that 5 -lipoxygenase has an ATP binding site and suggest that self-associatio n of 5-lipoxygenase in 20 mu M Ca2+ may affect ATP binding affinity as measured by Scatchard analysis.