DPN, DPNH

Fig. 5. A, left ordinate Effect of pH preincubation with OP on inhibition of ADH activity. Preincubation conditions ADH 5 X 10 M OP, 0°C., 60 minutes. Activity measurements the rate of DPN — DPNH, pH 8.8, 23°C. is measured. Each point represents an activity measurement after preincubation with the inhibitors (Vi) as a percentage of the uninhibited control (Po).

As has been indicated, inhibition does not occur without preincubation with the agents studied. Figure 7 shows ADH activity as a function of time in the presence and absence of 2 X 10 M OP at 0° C., pH 7.5. In 5 hours, activity of the uninhibited enzyme falls slowly to 80 % of the original value, whereas in the presence of OP it falls to 17.5% as measured by the rate of oxidation of ethanol (DPN —> DPNH). During the same period, activity of the uninhibited enzyme falls to 72.5 %, and in the presence of... 

Fig. 7. Effect of time of prcincubation on inhibition of ADH activity by OP. Preincubation conditions ADH 2 X 10 M OP, pH 7.5, 0°C. Activity measurements aliquots are removed from the same preincubation mixture at the times indicated. The rate of DPN DPNH at pH 8.8, 23°C., or the rate of DP.NH —> DPN at pH 6.5, 23°C., is measured. [From Vallee and Hoch, 1955b]...

DPN (1 M) (in the presence of catalytic amounts of alcohol dehydrogenase) at pH 7.0 may be used to illustrate the calculations. In this example, one half-reaction is the ethanol-acetaldehyde couple, which has an Eo of —0.200 volts the other couple, DPN-DPNH, has an Ed of... 

The effect of pH on oxidation-reduction potentials can be illustrated with the alcohol dehydrogenase system. Instead of pH 7.0, consider the reaction at pH 11.0. The acetaldehyde-ethanol couple will have an Eo of -0.200 - (4 X 0.06) = -0.440. The DPN-DPNH couple, involving only 1 hydrogen ion, changes from —0.320 to —0.440 volts. AE now is zero, and log IT, is zero. Ken, therefore, is 1. 

DPN, DPNH diphosphopyridine nucleotide, reduced diphosphopyri-dine nucleotide... 

Recent calculations which take into account the corrected value of 0.320 for the Ei value of the DPN-DPNH couplet show that the AFJ for the hydrolysis of the pyrophosphate bond in ATP is —8,640 calories (Anfinsen and Kielley, personal communication). If this value is correct, the AFo for the hydrolysis of thiolesters, acetyl-P and N-acetyl imidazole will be about —8,600, —11,200 and —14,000 calories respectively instead of the higher values which are reported in this paper. 

In the course of the successive dehydrogenations of the cycle, the greater part of the protons and electrons liberated pass. to the same series of carriers. The first acceptor of the series being most often DPN+, DPNH appears as the principal fuel in cells. 

A relatively nonspecific adenyl deaminase has been purified from Aspergillus oryeae which deaminates, in descending order of rate, adenosine, adenosine 5 -phosphate, adenosine 3 -phosphate, ATP, adenosine diphosphate (ADP), DPN, DPNH, and adenosine-diphosphate-ribose. Adenine, TPN, and adenosine 2 -phosphate are unaltered by the enzyme (29). A... 

However both can be cleaved by alkali to form UMP and the phosphate derivative of the carbohydrate. The pyrophosphate bond may also be split by a nucleotide pyrophosphatase from potatoes (338) or kidney (339). The enzyme is effective on DPN, DPNH, TPN, ADP, ATP, thiamine pyrophosphate, and FAD. 

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