CYTOPLASM 



141 



pounds, such as sugars, amino acids and amides, are lost; hence the 

 proportion of insoluble proteins is increased. It is noteworthy that 

 the proportion of lipids is very low. The considerable "unknown" 

 fraction probably comprises the nucleic acids, which in the present 

 case have not been separately determined. 



b. Physicochemical Behaviour of Proteins 



Si^e of globular protein f/wlecules. The molecular weight of globular 

 proteins can be determined with the aid of the ultracentrifuge. 

 SvEDBERG has found that the weights of quite different proteins are 

 similar. Thus the molecular weight of pepsin, insuHn and egg albumin 

 is 34,500 (SvEDBERG, i93i).In many instances there is an approximate 

 multiple of this figure, such as 70,200 for horse serum-albumin. After 

 a systematic investigation, Svedberg (1938b) came to the conclusion 

 that in protein molecules there is a fundamental unit of molecular 

 weight 17,600. 



TABLE X\' 

 WEIGHTS AND SIZE OF GLOBULAR PROTEIN MOLECULES 



Substance 





 ci. 



Q 



> 



J3 



EC 



3 



c ^ 



O O 



£ 'E 

 I S ° 



k -^ 



Lactalbumin a, rnyoglobin i 17600 200 



Lactoglobulin, ovalbumin, zein, pepsin, 



insulin 2 35 200 400 



Serum albumin, CO-haemoglobin, yel- 

 low ferment 4 70400 800 



Serum globulin 8 140800 1600 



Edestin, excelsin, phycocyanin, phyco- I 



erythrin, catalase 16 281600 3200 



Haemocyanin (cleavage component), | 



urease 24 422400 4800 



Haemocyanin (cleavage component). . 48 845 000 9 600 



Haemocyanin (Calocaris) j 96 1690000 19200 



Haemocyanin (Rossia) I 192 13380000 38400 



Haemocyanin (Helix pomatia) .... 1-384 6760000 j 76800 



c 



c 



34.5 2.87 1.8 I 0.07 

 43.5 5-75, 2.o; 0.14 



