1921] Quality of Protein in Nutrition 341 



WEEKLY EVENING MEETING, 



Friday, April 8, 1921. 



Sir James Crichtox-Browne, J.P. M.D. LL.D. F.R.S., 



Treasurer and Vice-President, in the Chair. 



R. H. A. Plbdier, D.Sc., 



Biochemist, Rowett Research Institute of Animal Nutrition, 



University of Aberdeen, 



and North of Scotland College of Agriculture. 



Quality of Protein in Nutrition. 



[Abstract.] 



Of the three main groups of compounds composing our normal 

 diet, protein is the only one which shows any marked variation. 

 The carbohydrates and fats are converted during digestion into a 

 few simple compounds, such as grape sugar, glycerin and fatty acids. 

 Protein is also converted during digestion into simple compounds, 

 but their number and variety is large, and different amounts of 

 them arise from the different proteins. We can thus speak of quality 

 of protein, but not of quality of carbohydrate and fat. 



Our usual classification of proteins already indicates their differ- 

 ences, but the variety is really far greater. We need only refer to 

 their chemical analysis. Fischer and Kossel and their pupils have 

 shown that proteins on hydrolysis break down into some eighteen or 

 twenty amino acids. These numerous products can be arranged for 

 convenience into eight groups : — 



I. — Simple Mono-amino Acids. 



Glycine CH 2 (NH 2 ).COOH 

 Alanine CH 3 . CH(NH,) . COOH 

 Valine (CH 3 ), : CH.CH(NH 2 ).COOH 

 Leucine (CH 3 ) 2 : CH.CH 2 .CH(NH 2 ).COOH 

 Isoleucine (CH 3 ) (C 2 H 5 ) : CH . CH(NH 2 ) . COOH 



II. — Mono-amino Dibasic Acids. 



Aspartic Acid HOOC . CH 2 . CH(NH,) . COOH 

 Glutamic Acid HOOC . CH 2 . CH 2 . CH(NH 2 ) . COOH 



III. — Hydroxy-amino Acids. 



Serine CH,OH.CH(NH 2 ).COOH 



Hydroxyglutamic Acid HOOC . CH 2 . CHOH . CH(NH 2 ) . COOH 



