A general colorimetric procedure for the estimation of enzymes which are linked to the NADH/NAD+ system

1. I. Two colour reactions for determining the reduced coenzyme NADH are described. 1.1. (a) A coloured formazan is produced by the reduction of the tetrazolium salt INT with NADH, electron transfer being facilitated by PMS ; the formazan is stable and the extinction is read at 500 mμ. 1.2. (b) The coloured ferrous dipyridyl complex is produced following the reduction of a ferric salt with NADH, in the presence of PMS; the coloured complex is stable for 30 min. The extinction is read at 520 mμ. I μmole of NADH, when reacted with the ferric salt, gives the same absorbance as 2 τmmoles of a ferrous salt, and it is possible to standardise the solution of NADH against a stable iron standard without the need for an ultraviolet spectrophotometer. 2. 2. Details are given of tlie assay of HBD, LDH, SDH, MDH and GOT, GPT, using these colour reactions, micro-volumes of sample being used. 3. 3. Details are given of standard deviation, cost, reliability, etc., of the methods described. 4. 4. Present methods for the assay of GOT and GPT are discussed in the light of recent literature.