Figure 3.

pH dependence of different forms of isoprene synthase with activity normalized to maximal activity. A, Profiles for thylakoid-bound isoprene synthase and solubilized thylakoid-bound isoprene synthase. The maximal isoprene synthase-specific activities for the thylakoid-bound and solubilized thylakoid-bound isoprene synthases are 30.8 and 209 pmol isoprene min⁻¹ mg⁻¹, respectively. B, pH curves for soluble isoprene synthase from a willow leaf-fractionation experiment (stromal) and for leaf-soluble isoprene synthase (obtained by grinding whole leaves in liquid nitrogen). The maximal isoprene synthase-specific activities for these samples are 75.3 and 166 pmol isoprene min⁻¹ mg⁻¹ for the stromal and leaf soluble isoprene synthases, respectively. Details for the thylakoid-bound isoprene synthase pH experiments are given in Wildermuth and Fall (1996). pH profiles for the other isoprene synthases were conducted similarly, as described in Methods. Results above are from a typical experiment, repeated several times.