The light activation of the hydrogenase of Proteus vulgaris previuosly observed in whole cells has been demonstrated in cell-free extracts and in the particulate hydrogenase obtained from such extracts. The particulate hydrogenase was solubilized by treating it with deoxycholate at pH 8.0 and was further purified by (NH4)2SO4 fractionation, by heating at 60° and by Sephadex chromatography. This procedure afforded a 65-fold purification, and all fractions exhibited light activation of the hydrogenase, suggesting that light directly affects the hydrogenase. A comparison of the light-activated purified enzyme and the one active in the dark showed that there was no difference in the molecular weight (115 000), in the mechanism of hydrogen activation or in the Km for hydrogen, while vmax was greater for the light-activated enzyme. The mechanism of light activation is discussed in terms of these findings.
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