FIGURE 3.

Substrate specificity and pH dependence of PME3-His₆. A, HG isolation and tailoring. Lime pectin was first saponified before HG isolation. The recovered HG0 was then highly methylated (96%, HG96). HG96 was further chemically (B-series) or enzymatically (P-series) demethylesterified to reach a specific DM. In the BP series, HG96 was first given alkaline base treatment before further action of orange PME. B, purified PME3-His₆ activities assayed at three pH values (pH 7.5, 6.0, and 4.0) on various HG substrates with different lengths and degrees of methylation. Activities were determined colorimetrically using N-methylbenzothiazolinone-2-hydrazone and alcohol oxidase for released methanol oxidation. Data represent means ± S.D. (error bars) from three replicates. C, PME3-His₆ enzyme activity assayed at pH 7.5 on HG substrates (B-series) with different lengths and a similar degree of methylation (HG96B69, HG37B72, and HG12B71). Data represent the means ± S.D. of three replicates. The different letters indicate data sets significantly different according to Tukey's range test, preceded by a one-way ANOVA having p < 0.001.