To measure oxygen-sensitive pyruvate formate-lyase (EC 2.3.1.54) activity, a spectrophotometer was placed in an anaerobic glove box (90% N2, 10% H2) . The activity of pyruvate formate-lyase of Streptococcus mutans strain NCIB 11723 obtained by this method was at least eightfold higher than that obtained by the Thunberg tube method. This assay method is considered more accurate and more sensitive, and it allows a continuous assay of the enzyme activity when lactate dehydrogenase activity is

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... t in the assay mixture. When pyruvate formate-lyase was incubated with a low concentration of oxygen, the activity was decreased with time. At a fixed concentration of oxygen the lower the concentration of the enzyme was, the more activity was lost. The inactivation by oxygen was ascribed to the production of neither superoxide nor hydrogen peroxide but molecular oxygen itself. It was suggested that this method could be used for the accurate assay of not only pyruvate formate-lyase but also other oxygen-sensitive enzymes.