THE SYNTHESIS OF THE PROTEINS 7 



leucine ester and tyrosine ester with glycine ester, whereby he obtained 

 a peptone-like body giving all the principal protein reactions. 



Another anhydride of glycine was obtained in 1900 by Balbiano and 

 Trasciatti who heated glycocoll with glycerol ; it was a yellowish powder 

 insoluble in all neutral solvents, like the horny substances, and on 

 hydrolysis Balbiano found that it was reconverted into glycine. 



Not, however, until 1904 were any further investigations carried out 

 concerning the constitution of the biuret base. Schwarzschild then 

 suggested that it consisted of seven glycine molecules combined together 

 in an open chain, and that it was the ethyl ester of hexaglycyl-glycine 

 of the formula 



NH 2 . CH 2 . CO (NH . CH 2 . CO) 5 NH . CH 2 . COOC 2 H B , 



but Curtius shortly afterwards showed that this was erroneous, and that 

 the body with which Schwarzschild had worked was still a mixture of 

 glycine anhydride and biuret base. 



By studying the conditions under which glycine ester was converted 

 into glycine anhydride and biuret base, Curtius showed that, when 

 moisture was excluded as completely as possible, the biuret base with 

 only traces of glycine anhydride was formed, and that the amount of 

 glycine anhydride produced increased with the amount of water present. 

 Thus, if pure glycine ester were kept in the absence of air, it solidified 

 in a few days and the mass contained biuret base with 23-24 per cent, 

 of glycine anhydride ; if glycine ester were boiled with dry chloroform, 

 12 per cent, of glycine anhydride was formed, but if perfectly pure 

 glycine ester were mixed with about a third of its volume of absolute 

 ether and left for some weeks it was almost completely converted into 

 biuret base, only i per cent, of glycine anhydride being present. The 

 analysis, molecular weight, properties and reactions of the biuret base 

 showed conclusively that it was triglycyl-glycine ester, i.e., a. tetra- 

 glycyl compound of the formula 



NH 2 . CH 2 . CO NH . CH 2 . CO NH . CH 2 . CO NH . CH 2 . COOC 2 H . 



It was observed by Curtius and Gumlich that the biuret base when 

 heated in vacuo to 100 C. lost alcohol, and that it was converted into 

 an anhydride, most probably octoglycine anhydride, so that from 

 glycine ester quite complex substances can be obtained. Such sub- 

 stances have also been obtained by Emil Fischer and his pupils by the 

 condensation of amino acid and polypeptide esters (see below). 



