A new method of measuring protein-methionine-s-oxide reductase activity.

A new assay for measuring protein-methionine-S-oxide reductase is reported. The assay measures the conversion of N-(9-fluorenylmethoxycarbonyl)-methionine sulfoxide to N-(9-fluorenylmethoxycarbonyl)-methionine using fluorescence detection after high-performance liquid chromatography separation. Enzyme activity is linear over a 60-min period and the assay is sensitive enough to detect the consumption of only 1% of available substrate. Protein-methionine-S-oxide reductase activity was demonstrated in pea (Pisum sativum L.) chloroplasts, and enzyme levels in leaves of etiolated and light-grown seedlings were compared.