Abstract
In order to facilitate the development of satisfactory histochemical methods for reduced pyridine nucleotide oxidative enzymes, studies with sucrose homogenates of rat brain were undertaken. For this purpose either oxygen or an N-thiazol substituted monotetrazole were used as final electron acceptor. (A quinone (menadione) was used as an intermediary carrier.Comparable activities with both NADH2 and NADPH2 were obtained with the mitochondrial and cytoplasmic fractions.Tetrazoliu reduction by enzymically formed hydroquinone was faster than its autoxidation, independent of pH. Kinetic activation of menadione reduction was achieved by irreversible removal of hydrogen by formazan formation. An equimolar relationship was found between reduction of monotetrazole and oxidation of reduced pyridine nucleotide substrate.Comparison of apparent Km values at the optimum pH suggested a close relationship between mitochondrial and extramitochondrial menadione reductase. The kinetic data indicate that mitochondrial NADH2-NADPH2-tetrazoliu reductase is not the same enzyme as menadione reductase.It is suggested that tetrazolium methods can be used for parallel studies of the activity of alternative pathways of electron transport in tissue fractions and sections.
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