170 



properties of the acid were developed and could be titrated as any organic 

 acid. 



8. P. L. Sorensen worked out the details and made it possible to estimate 

 amino acids quantitatively by means of formaldehyde. It is well known that 

 amino acids, such as are formed by the hydrolysis of proteins, especially 

 milk prqteids, are neutral to phenolpthalein, have both an acidic group, 

 earboxyl and a basic (amino) group. These exist in the same molecule and 

 being the alpha amino acids neutralize each other, or in other words we have 

 an amphoteric- mole3ule, but as soon as formaldehyde is added, it reacts 

 with the alkaline or basic group forming a methylene compound and leaving 

 the ac-id group free to act. 



For example : 



/NH, /N = CH 4 



CH 3 - CH + HCOH = CH 3 - CH, +- H 2 



X COOH COOH 



(Alanine) (Formaldehyde) 



/N - CH 2 /N = CH 4 



CK : - CH + KOH = CH 3 - CH^ + II .0 



X C00H COOK 



From Emil Fisher's researches on protein and polypeptids there is no 

 doubt that the protein molecule is conposed of amino acid units. The 

 earboxyl group (—COOH) of one amino acid is combined with the amino 

 group ( — XH 4 ) of another amino acid, forming peptids, di, tri, etc., to poly- 

 peptids. For example, glyeyl-glycine composed of two units of gyleine. 



CH- - C0X>H\ CH 2 - COOH CII; CO - CH : - COOH 



= [ | + H,0 



H 2 N "N?" N - H H 2 N NH 



(Glycine) (Glycine) (Glycil-G'ycine) 



Likewise different units may combine, as example, alanyl-glycyl-tyrosine 

 From which we see that each peptid has one earboxyl ( group (—COOH) 

 acidic and one amino group ( — NH 2 ) basic Xow if the protein molecule 

 is built up from amino acids, we can expect it to split up into simpler mole- 



