18 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



densed leucine ester and tyrosine ester with glycine ester and 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 like the horny substances insoluble in all neutral solvents, 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, . CH, . CO (NH . CH, . CO) e NH . CH, . COOC,H 6 , 



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 having the formula 



NH, . CH, . CO NH . CH, . CO NH . CH, . CO NH . CH, . COOC,H B . 



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

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

 an anhydride, most probably octaglycine anhydride, so that glycine 

 ester forms a starting point from which quite complex substances can 

 be derived. Such substances have also been obtained by Emil Fischer 

 and his pupils by the condensation of amino acid and polypeptide 

 esters, p. 29. 



