RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICULTUilAL CHEMISTRY— AGROTECHNY. 



On the origin of the humin formed by the acid hydrolysis of proteins. — ■ 

 IV, Hydrolysis in the presence of aldehydes. — III, Comparative hydrolysis 

 of fibrin and gelatin in the presence of various aldehydes, G. E. Holm and 

 R. A. GoRTNEE (Jour. Aiiier. Clwm. Soc, 42 (1920), No. 3, pp. 632-640, fig. i).— 

 The observations previously noted (E. S. K., 38, p. 201) regarding the hy- 

 drolysis of fibrin and gelatin in the presence of formaldehyde have been ex- 

 tendetl to include a study of the effect of benzaldehyde, acetaldehyde, and 

 butyric and isobutyric aldehydes. 



As no fibrin such as was used in the previous experiments could be obtained, 

 certain of the experiments with formaldehyde were also reiieated with the new 

 material, which consisted of commercial fibrin from blood puritieil by dissolv- 

 ing in 0.2 per cent NuUH, filtering through four double cheesecloths, pre- 

 cipitating with HCl, washing the precipitate until free of HCl, and drying 

 and grinding the product. The method followed was the same as that u.sed in 

 the former experiments with the exception that hydrolysis was continued for 

 24 hours only, and that, in addition to the other determinations, the total 

 amino nitrogen was determined in the filtrate from the soluble humin. 



The data obtained with formaldehj'de confirm the conclusions of the previous 

 paper. With benzaldehyde in increasing aniDunts, there was an increase in the 

 amount of insoluble humin up to a constant value, but no increase in ammonia 

 or soluble humin. Since it has been shown by Gortner (E. S. R., 36, p. 108) that 

 when fibrin is hydrolyzed with HCl in the presence of benzaldehyde a large 

 part of both tryptophan and tyrosin remain in the acid-insoluble humin, the 

 maximum amount of insoluble humin is considered to be derived front trypto- 

 phan and tyrosin present in the gelatin and fibrin. As the insoluble humin ob- 

 tained in the presence of formaldehyde has been shown in the preceding paper 

 to be derived almost exclusively from tryptophan, the authors conclude that 

 " by utilizing both the formaldehyde and benzaldehyde data one may estimate 

 at least the minima tryptophan and tyrosin content of a protein." 



The action of butyric and isobutyric aldehydes upon protein hydrolysis was 

 sinnlar to the action of benzaldehyde with the exception of the possible adsorp- 

 tion or occlusion of other nitrogen compounds due to polymerization of the 

 aldehydes. Consistent results were not obtained with acetaldehyde, probably 

 on account of its rajad polymerization. 



The total amino nitrogen in the filtrate fron* the soluble humin fell rapidly 

 with the addition of increasing amounts of formaldehyde, while there was at 

 the most only a slight decrease in the amino nitrogen figures in the case of the 

 other ald(>hydes. 



" Our data confirm the conclusion that the formation of the black acid- 

 insoluble humin in a normal protein hydrolysate (only protein and acid present) 

 is dependent upon the presence of trytophan in the protein molecule, and the 

 only part which any of the other known amino acids has in such humin forma- 

 tion is to (perhaps) furnish an insignificant amount of nitrogen to the humin 

 fraction through either adsorption or occlusion." 



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