19C) BACTERIOLOGICAL CHEMISTRY 



selectively adsorb different types of compound which 

 have a corresponding arrangement of their own polar 

 groups (see p. 31). Thus sugars are adsorbed by one 

 grouping, succinic and similar acids by another sort of 

 grouping, lactic and other hydroxy-acids by a third 

 grouping, and so on. Once this specific adsorption has 

 occurred the general mechanism of the activation is the 

 same in each case. As would be expected, substances 

 having a configuration similar to those activated, but 

 which are themselves not activated (possibly because 

 the field of force is not strong enough), will partially 

 inhibit the activation of the latter, since they can 

 be adsorbed on to the active centres to the partial 

 exclusion of the normal substrate. For example, «-hy- 

 droxybutyric acid, CH3CH2CHOH.COOH, or tartaric 

 acid, COOH.CHOH.CHOH.COO^, will inhibit the activa- 

 tion of lactic acid, CH3CHOH.COOH, in virtue of the 

 common structure — CHOH.COOH which enables them 

 to compete for places at the active centres ; but they 

 will not inhibit the activation of succinic acid, 

 COOH.CH2.CH2.COOH, because it is adsorbed at different 

 active centres not affected by the hydroxy-acids. Con- 

 versely malonic acid, COOH.CHg.COOH, or glutaric acid, 

 COOH.CH2.CH2.CH2.COOH, will inhibit the activation of 

 succinic acid but not that of lactic acid, because they are 

 adsorbed on the same centres as succinic acid which has 

 the common group, — CH2.COOH. This suggestion of 

 competitive adsorption at enzyme centres has also been 

 used in the explanation of the mode of action of chemo- 

 therapeutic substances (see Chapter X). 



Warburg suggested that all aerobic oxidations, that is, 

 those in which atmospheric oxygen is involved, are brought 

 about through the intervention of iron compounds, such 

 as haemoglobin, whereby molecular oxygen is transferred 

 to the substrate in an activated form. He showed that 

 amino-acids could be oxidised l)y molecular oxygen when 

 at the surface of charcoal prepared by licating blood, and 



