Lactic acid dehydrogenase (LDH) activity in whole blood or serum has been proved by various investigators. Most of their methods for the estimation of LDH activity were electrophotometric determination of the reduction of diphosphopyridine nucleotide.
The author tried to estimate LDH activity with the use triphenyl tetrazolium chloride (TTC). The reduction of TTC was, however, not observed at all.
The blood constituents were added to the reaction mixture in phosphate buffer containing TTC lactate and lactic dehydrogenase obtained from guinea pig liver,
Results indicated that TTC reduction was inhibited by the addition of red blood cell. the nature of inhibition were summaried as follows.
1. The inhibitory action of red blood cell could tolerate against the temperature of 58°C and survive 65°C for 5 minutes.
2. When the red blood cell was treated with acetone, the inhibitor was not found in the solution, and precipitated completely.
3. The inhibtory action was found in the blood of rabbit, guinea pig, sheep and also of human beeing.
4. The mechanism of this action was supposed to the substance contained in red blood cell, which inhibited hydrogen transfer from lactic acid to TTC.
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