PENICILLIN AND STREPTOMYCIN 199 



CH, 



CH, 



CH — COOH 



S^ N 

 \ / \ 

 HC C = 

 \ / 

 CH 

 I 



NH 

 I 



CO 

 I 



R R = ^_J>-CH2- (Penicillin l) 



= CH3CH2CH = CH-CH2- (Penicillinn) 

 Formula of Penicillin. 



2. Streptomycin: a substance excreted by the mould 

 Streptomyces griseus and active against both Gram-positive and 

 Gram-negative bacteria. Its use in medicine is restricted since 

 many pathogenic organisms rapidly acquire resistance against 

 it. Streptomycin is the first antibiotic to be effective against the 

 tubercle organism in vivo and it has been of great use in com- 

 bating tuberculosis. Attempts are being made to extend its 

 cHnical usefulness by giving it in conjunction with some other 

 drug such as a sulphonamide or sulphone which, by preventing 

 multiplication of the organisms, will also prevent acquirement 

 of resistance to streptomycin. The formula is given below. 

 Streptomycin may act as a nutritional antagonist as its 

 structure contains the unnatural analogue of glucosamine and 

 a possible analogue of inositol. Its mode of action is not yet 

 clear; experiments with intact sensitive cells suggest that it 

 interferes with some stage in the oxidation of pyruvate. The 

 stage affected is concerned with a reaction involving pyruvate 

 and oxalacetate, possibly a condensation similar to that 

 occurring in the citric acid cycle (see p. 153). However, it is 

 not known whether this cycle functions in bacteria and no 

 demonstration of an action of streptomycin on a cell-free 

 bacterial system has yet been pubhshed. 



