186 Discussion 



This is extremely high and, therefore, not only diabetes but also general 

 damage might possibly have occurred. 



Hess: In relation to Prof. Holzer's comment and Prof. Dickens' 

 answer on the pyruvate-lactate equilibrium in animal tissue, I might 

 mention that we have already done this type of analysis, and also with 

 similar substrate redox systems, in our laboratory. Dr. Czok, in Prof. 

 Biicher's group, is also engaged in these studies. We applied the method 

 to human blood which was withdrawn under resting conditions and 

 under various pathological conditions. Since lactic dehydrogenase is 

 very strongly concentrated in human tissue (unpublished data), and 

 since there is no diffusion problem for both lactate and pyruvate, the 

 ratio of both substrates measured in venous or arterial blood reflects the 

 overall ratio of the tissue, muscle playing the largest part. Under 

 normal conditions we find a molar lactate /pyruvate ratio of 12-97 

 corresponding to a substrate redox potential of E'h == —222-9 mv. 

 Thus, using Racker's equilibrium constant for lactic dehydrogenase for 

 the calculation of the DPN/DPNH ratio, we obtain a value of 1927. 

 Under hyperglycaemic conditions in normal patients, the lactate/ 

 pyruvate ratio is shifted to 19-14 (case no. 2b) or 26-5 (case no. 3). 

 Under hyperglycaemic conditions in diabetic patients the ratios were 

 23-3 (case no. 18) or even 35-6 (case no. 19). The latter value, cal- 

 culated for the DPN/DPNH ratio, would be 700. This drop in the ratio 

 (Hess, B. and Gottschling, H. (1959). In preparation) is in agreement 

 with the data presented by Prof. Dickens. 



Dickens: Is that ratio the same as that of the total amounts of 

 oxidized and reduced pyridine nucleotide actually present in the animal 

 tissues? 



Hess: Yes, just the same. 



Potter : Prof. Biicher and his co-workers at Marburg are carrying out 

 quite extensive studies on this in terms of lactate and pyruvate, and 

 also in terms of dihydroxy acetone and a-phosphoglycerol. 



King: In connexion with Prof, de Duve's comment on the conversion 

 of glucose to fructose via sorbitol. Dr. Mann and I have found that 

 this occurs not only in seminal vesicles, but also in spermatozoa per se. 

 We have isolated soluble sorbitol dehydrogenase from spermatozoa and 

 purified it to some extent. We believe that this sorbitol dehydrogenase 

 in spermatozoa acts as a regulatory factor for the various activities 

 which require pyridine nucleotide, since semen contains no glucose, but 

 only fructose. Therefore, by this series of reactions the pyridine 

 nucleotides, oxidized or reduced, can be supplied, depending on the 

 prevalent conditions (e.g. concentrations of reactants) which can 

 certainly affect the direction of this series of reversible reactions. 



Prof. Dickens, you indicated that CO 3 came either from the Embden- 

 Meyerhof or from the pentose phosphate pathway. How can you 

 differentiate between the two? 



Dickens : We cannot ; but by using glucose labelled in positions 1 and 

 6 and comparing the yields of ^^COg then obtained, one can calculate the 

 probable relative extent of the pathways, on the assumption that 

 the C-1 comes off first in the oxidative pentose phosphate pathway. 



