Methionine Content of the Animal and Plant Organism 575 



On giving cysteine labelled with ^^S to chick embryos MachHn, Struglia & 

 Pearson [ii] found 1-3% of the labelled siilphur in methionine and 49% in 

 cysteine j on giving methionine labelled with ^^S they found 35% of the radio- 

 active sulphur in methionine and 43% in cysteine. 



In the work of Rose & Wixon [15] on the correlation between cysteine and 

 methionine it was shown that, in man, after the administration of DL-cystine, 

 the metliionine requirement declines sharply (80-90%), which gives reason to 

 beheve in the formation of methionine by the agency of cysteine. 



On the basis of the evidence of the current literature, as well as our own, we 

 set ourselves the task of extending the study of the effects of methionine and 

 cysteine on the metabolism of these sulphur-containing amino acids in other 

 species of old animals as well, and also in the mould Aspergillus niger. 



Table i gives the results of experiments on old rats, guinea pigs, rabbits and 

 dogs. 



Intramuscular administration of cysteine or methionine to rats, guinea pigs, 

 rabbits* and dogs (50 mg/kg of body weight for 16 days) leads, in all the 

 animals, to an increase in the methionine content. 



As cysteine (cystine) enters into the composition of glutathione we deter- 

 mined the content of oxidized, reduced and ordinaiy glutathionef in rats of 

 various ages after giving cysteine and methionine (50 mg/kg of body weight for 

 16 days) (Tables 2 and 3). 



Table 2 



Mean content of oxidized^ reduced and ordinary glutathione in rats of 



various ages 



Oxidized Reduced Ordinary 



glutathione glutathione glutathione 



(mg/ioo ml blood) 



YOUNG ANIMALS 



3-30 30-9 34-1 



(-i-i; +0-8) (-0-20; +0-3) (-1-5; +i-o) 



ADULT ANIMALS 



7-IO 29-9 37-5 



(-o-5i +0-7) (-3-5; +1-2) (-3-70; +1-9) 



OLD ANIMALS 



7-65 28-8 36-5 



(-0-45; +1-05) (-o-20i +o-i) (-0-3; +0-9) 



Note: The figures in brackets show the derivation of maximal and minimal values from 

 the mean. 



* In rabbits there is an insignificant increase in the methionine content after giving 

 cysteine. It must be borne in mind that, owing to their intolerance of the large dose of 

 cysteine, these animals only received a half dose of 25 mg/kg of body weight. 



t The oxidized, reduced and ordinary glutathione were determined by the method 

 of Woodward & Fry [23]. 



