Kinetic studies of nitrogenase from soya-bean root-nodule bacteroids |
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Authors: | F. J. Bergersen and G. L. Turner |
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Affiliation: | Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, Canberra, A.C.T. 2601, Australia |
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Abstract: | The apparent Michaelis constants [K'(N(2)) and K'(C(2)H(2))] and the corresponding apparent maximum velocity values (V') for soya-bean bacteroid nitrogenase increased concomitantly in response to increases in nitrogenase Fe-protein concentration and ATP concentration in cell-free assays and in response to O(2) pressure in intact nodules and bacteroid suspensions. K'(C(2)H(2)) in cell-free assays was also affected by pH and by Na(2)S(2)O(4) concentration. Nitrogenase Fe-protein behaved as a catalytic effector reacting at interacting sites on the nitrogenase Fe-Mo-protein. The results indicated that the Fe-Mo-protein probably bears the catalytic sites for N(2) and C(2)H(2) reduction. It is concluded that reduction of N(2) or C(2)H(2) by this nitrogenase involves a reaction mechanism with a sequence of unknown order. The sequence in which substrate, enzyme, effector, ATP and reductant react determines which of the various rate-constants are involved in the apparent Michaelis constant, whose true kinetic meaning was thus unresolved. |
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