CHEMOTHERAPY 



of gramicidin as an example ol noncompetitive inhibition of some 

 enzyme involved in a phosphorylating system. Tlie effect can be 

 studied in cell-free systems, since muscle and kidney extracts are pre- 

 vented by this same agent from phosphorylating glucose, although the 

 oxidation which normally furnishes energy for the phosphorylation 

 continues unaffected. It is to be expected that future work with cell- 

 free preparations will reveal exactly which of the energy-utilizing 

 systems is being blocked, and at the same time provide a specific 

 inhibitor for use in the study of this important function in the bio- 

 chemical laboratory. 



Tyrocidine is found to contrast sharply with gramicidin in 

 mechanism of action. Bacteria exposed to it respire at such a low 

 rate that syntheses and growth are not possible, if only for the reason 

 that energy is not made available rapidly enough. Yet it is note- 

 worthy that respiration, easily reduced to 5-10% of its normal rate, 

 appears to resist further reduction even when a tenfold excess of agent 

 is applied. This fact suggests that there is no single key enzyme being 

 inhibited by tyrocidine, but either that an organization of enzymes is 

 being rendered more inefficient or that an alternate, inefficient, meta- 

 bolic pathway is being utilized which is less susceptible. At this point 

 let us recall that tyrocidine, with its basic group and alcohol-soluble 

 side chains, has a pronounced surface activity. Like the natural 

 saponins and bile salts, and the synthetic detergents, wetting agents, 

 etc., it can bring about hemolysis of red blood cells. If it were to 

 produce an analogous injury to bacteria, we should have, as with the 

 hemoglobin of erythrocytes, various soluble cellular metabolites 

 liberated from the cells into the surrovmding medium. There is un- 

 mistakable evidence that exactly this sort of damage is produced by 

 tyrocidine; and, in exposures at different time, temperature, or con- 

 centration, it happens in just those cases in which the bacteria are 

 killed. Appropriate analyses show that five-minute exposure to about 

 one-hundredth their weight of tyrocidine at zero degrees centigrade 

 is sufficient to extract quantitatively from staphylococci the total tri- 

 chloroacetic-acid-soluble phosphorus and nitrogen compounds present 

 in the cell. Analyses have been made for such typical constituents as 

 inorganic phosphate, adenosine triphosphate, other phosphate esters, 

 total esters, total nitrogen, amino nitrogen, amino acids, and pentoses. 

 Analogous effects have been observed with other microorganisms. So 



