Complex Compounds and Models of Enzymes 



273 



In our laboratory V. V. Yushina [19] has studied models of dehydrogenases 

 which consisted of a dyestuff whoch could be transformed into a leuco form, thus 

 serving as a model of the active group of dehydrogenase and a carrier of a 

 carbohydrate- or protein-like character. In particular, it was established that 

 methylene blue and thionine could catalyse the oxidation of pyrogallol, metol 

 and an aqueous solution of hydrogen sulphide by oxygen. The activity of the 

 dyestuff was markedly increased by its adsorption on pastes of starch, dextrin, 

 albumin and cellulose. The association of the dyestuff with the substances of 

 high molecular weight even gave rise to a certain specificity in respect of the 

 substrate. Thus, adsorption of thionine on starch or dextrin gives a catalyst 

 which has an increased activity in respect of the oxidation of metol (Fig. 4). 

 Methylene blue on starch is effective in the oxidation of pyrogallol. 



Fig. 4. The taking up of oxygen by solutions of metol at pH 7-2 and 27°C. 



I = metol (10 mg/ml.) 

 II = metol + thionine 

 III = metol + thionine + starch (0-03%) 

 Volume of solution = 45 ml. Concentration of thionine = 00012%. 



e 



8 



11 12 13 14 15 16 17 



9 10 



min 



Fig. 5. The taking up of oxygen from the air by an aqueous solution of hydrogen 

 sulphide. Concentration of H2S = 0-05 M. Temp. = 15-5 °C. In the presence of : 



I. 0-2 g cellulose 



II. 5 mg indigo carmine 



III. 0-2 g cellulose + 5 mg indigo carmine. 



Indigo carmine adsorbed on cellulose is a very active catalyst in the oxidation 

 of an aqueous solution of hydrogen sulphide by air [20] (Fig. 5). The rate of the 

 reaction is determined by the rate of formation of the leuco form, which is 



18 



