EXPERIMENT STATION RECORD. 



Vol. 38. Abstract Number. No. 3 



RECENT WORK IN AGRICULTURAL SCIENCE. 



AGKICULTUEAL CHEMISTRY— AGEOTECIINY. 



On the origin of the humin fornied by the acid hydrolysis of proteins. — 

 III, Hydrolysis in the presence of aldehydes. — II, Hydrolysis in the pres- 

 ence of formaldehyde, K. A. Goktner and G. E. Holm {Jotir. Amer. Chan. Soc, 

 39 iWn), No. 11, pp. 2477-2501, fig. i).— Continuing the work previously noted 

 (E. S. R., 36, p. 108) the authors, at the Minnesota Experiment Station, have 

 studied the reactions which take place when proteins are hydrolyzed in the 

 presence of formaldehyde, with special reference to the formation of the black 

 insoluble humin of protein hydrolysis and also, incidentally, to the composition 

 of the " soluble humin " and " ammonia " fractions. 



From the results it is concluded that " when proteins are hydrolyzed in tbe 

 presence of trioxymetbylene and the resulting hydrolyzate analyzed by Van 

 Slyke's method, the nitrogen distribution is so altered as to bear no resemblance 

 to tbe analysis conducted in the absence of aldehyde. When a protein contain- 

 ing tyrosin and trytophan is hydrolyzed with increasing amounts of trioxy- 

 metbylene, the figures for both insoluble and soluble humin nitrogen are rapidly 

 increased to a maximum, after which there is a sharp decrease in the nitrogen 

 ciirve of these fractions. The ammonia fraction, on the other hand, decreases 

 with the smaller additions of trioxymetbylene and then rises rapidly for larger 

 additions of aldehyde. When both tyrosin and tryptophan are absent from a 

 protein, hydrolysis in the presence of trioxymetbylene produces no change in 

 the insoluble or soluble humin nitrogen and only a steady increase in tlie 

 ammonia fractions. We have shown that the rise in the insoluble humin curve 

 and the formation of black insoluble humin is due to the presence of trypto- 

 phan in the hydrolyzate, and we believe that the maximum point on the insoluble 

 humin nitrogen curve coincides closely with the amount of tryptophan nitrogen 

 present in the hydrolyzate. An excess of trioxymetbylene largely inhibits the 

 formation of insoluble humin but does not break down insoluble humin which 

 has once been formed." 



Histidin and cystin were found not to be involved in the formation of black 

 insoluble humin as reported by Roxas (E. S. R., 36, p. 412), and it is believed 

 that tryptophan alone of all the hydrolytic products is involved in the reaction, 

 as previously reported by the authors. The formation of the humin is indi- 

 cated as being due to a combination of tryptophan with some unidentified alde- 

 hyde or ketone, and the only part which any of the other amino acids have in 

 the humin formation is probably to furnish some of their nitrogen, either 

 through adsorption or occlusion. " The a-amino group of the aliphatic side 

 chain of tryptophan is not involved in the primary reaction by which black 

 insoluble humin is formed. The pi-imary reaction concerns only the indol 



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