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Temperature dependence of NADPH oxidase in human eosinophils

Deri Morgan, Vladimir V. Cherny, Ricardo Murphy, Wei Xu,* Larry L. Thomas* and Thomas E. DeCoursey

The phagocyte NADPH oxidase helps kill pathogens by producing superoxide anion, O₂^-. This enzyme is electrogenic because it translocates electrons across the membrane, generating an electron current, I_e. Using the permeabilized patch voltage-clamp technique, we studied the temperature dependence of I_e in human eosinophils stimulated by phorbol myristate acetate (PMA) from room temperature to > 37°C. For comparison, NADPH oxidase activity was assessed by cytochrome c reduction. The intrinsic temperature dependence of the assembled, functioning NADPH oxidase complex measured during rapid temperature increases to 37°C was surprisingly weak: the Arrhenius activation energy E_a was only 14 kcal mol^-1 (Q₁₀, 2.2). In contrast, steady-state NADPH oxidase activity was strongly temperature dependent at 20-30°C, with E_a 25.1 kcal mol^-1 (Q₁₀, 4.2). The maximum I_e measured at 34°C was -30.5 pA. Above 30°C, the temperature dependence of both I_e and O₂^- production was less pronounced. Above 37°C, I_e was inhibited reversibly. After rapid temperature increases, a secondary increase in I_e ensued, suggesting that high temperature promotes assembly of additional NADPH oxidase complexes. Evidently, about twice as many NADPH oxidase complexes are active near 37°C than at 20°C. Thus, the higher Q₁₀ of steady-state I_e reflects both increased activity of each NADPH oxidase complex and preferential assembly of NADPH oxidase complexes at high temperature. In summary, NADPH oxidase activity in intact human eosinophils is maximal precisely at 37°C.

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