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Human brain 6-phosphogluconate dehydrogenase: purification and kinetic properties.

K S Weisz·P J Schofield·M R Edwards
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Abstract

6-Phosphogluconate dehydrogenase has been purified from human brain to a specific activity of 22.8 U/mg protein. The molecular weight was 90,000. At low ionic strengths enzyme activity increased, due to an increase in Vmax and a decrease in Km for 6-phosphogluconate, and activity subsequently decreased as the ionic strength was increased (above 0.12). Both 6-phosphogluconate and NADP+ provided good protection against thermal inactivation, with 6-phosphogluconate also providing considerable protection against loss of activity caused by p-chloromercuribenzoate and iodoacetamide. Initial velocity studies indicated the enzyme mechanism was sequential. NADPH was a competitive inhibitor with respect to NADP+, and the Ki values for this inhibition were dependent on the concentration of 6-phosphogluconate. Product inhibition by NADPH was noncompetitive when 6-phosphogluconate was the variable substrate, whereas inhibition by the products CO2 and ribulose 5-phosphogluconate and NADP+ were varied. In totality these data suggest that binding of substrates to the enzyme is random. CO2 and ribulose 5-phosphate are released from the enzyme in random order with NADPH as the last product released.

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BrainCationsChloromercuribenzoatesGluconatesHumansIodoacetamideKineticsMolecular WeightNADPOsmolar ConcentrationPhosphogluconate Dehydrogenasep-Chloromercuribenzoic AcidJournal ArticleResearch Support, Non-U.S. Gov't

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K S Weisz, P J Schofield, M R Edwards. 1985. Human brain 6-phosphogluconate dehydrogenase: purification and kinetic properties.. https://doi.org/10.1111/j.1471-4159.1985.tb05443.x

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