Interaction between hysteretic regulation and redox modulation of glucose‐6‐phosphate dehydrogenase from Anacystic nidulans

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Abstract
The glucose‐6‐phosphate dehydrogenase (G6PDH) of cyanobacteria is a hysteretic enzyme which is also subject to redox modulation [FEBS Lett. 126 (1981) 85–88]. We have found that the hysteretic and redox properties of G6PDH exhibit specific interactions: (1) The hysteretic forms of G6PDH (‘hypoactive’ ⇌ ‘hyperactive’), obtained at pH 7.5 and 6.5, respectively, differ in their redox properties. The ‘hypoactive’ form is easily activated by oxidation whereas the ‘hyperactive’ form is easily deactivated by reduction. (2) At low G6P concentrations (1 mM) only the oxidized form of G6PDH has significant activity. An increase in G6P level diminishes the difference between the activity of oxidized and reduced G6PDH forms.