SUMMARY: A method is presented for the estimation of uridine pyrophosphoglucose dehydrogenase activity in extracts of pneumococci; this utilizes C-labelled uridine pyrophosphoglucose (UPPG). This method overcomes the difficulty of the spectrophotometric assay caused by the presence of reduced diphosphopyridine nucleotide (DPNH) oxidase in such extracts. An investigation was made of the protective effects of catalase and thioglycollate on pneumococcal UPPG dehydrogenase. Both these substances prevented inactivation of this enzyme. The results suggest that inactivation is caused by hydrogen peroxide and that the point of attack on the enzyme is upon sulphydryl groups. The UPPG dehydrogenase activity of some capsulated and non-capsulated strains of type I pneumococcus was determined. The capsulated and some of the non-capsulated strains examined had considerable UPPG dehydrogenase activity except one strain which had negligible activity. The enzyme UPPglucuronic acid-4-epimerase from a type I pneumococcus required diphosphopyridine nucleotide for activity.


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