1 66 PHYSIOLOGY OF NUTRITION 



Myrosin occurs in the seeds of black mustard. It decomposes sinigrin 

 into mustard oil (allyl isothiocyanate), glucose and monopotassium sulphate.* 



The decomposition of simple proteins is brought about through the agency 

 of proteolytic enzymes. Glycerine extraction of this type of enzymes is not 

 always successful and the method of Neumeister 1 is to be recommended here. 

 Fresh fibrin (from blood), which has the power to absorb proteolytic enzymes 

 from their solution, is placed in an aqueous extract of the plant material to be 

 studied. After two hours the fibrin is removed, washed with water, and left 

 in a weak solution of oxalic acid, in a warm place. If proteolytic enzymes were 

 present in the original extract, the fibrin is completely dissolved after five or six 

 hours. In the control preparation the fibrin remains practically unchanged 

 after two days in the weak oxalic acid solution. 



No proteolytic enzymes are present in resting seeds, but Butkevich 2 has 

 isolated this kind of enzyme from germinating seeds. The sprouted seeds are 

 dried at a temperature of from 35 to 4o°C, and then pulverized, after which the 

 mass is extracted with ether and placed in water with an antiseptic (thymol). 

 The preparation is allowed to remain in a thermostat, with a temperature of 

 from 35 to 40 , for several days. Auto-digestion results, accompanied 

 by a decrease in the amount of protein material present. The proteolytic 

 enzyme is extracted with glycerine and the extract effects a cleavage of proteins, 

 with the formation of tryosin and leucin. Butkevich was unable to isolate 

 asparagin, but this is readily understood, since it is not a primary product in 

 the hydrolysis of proteins (see pp. 1 59-1 61). 



Saponification of fats and oils occurs in plants through the agency of 

 specific enzymes, the so-called lipases. 3 Lipase is now obtained for technical 

 purposes from fatty seeds. 4 



The enzymes thus far mentioned cause various hydrolytic decompositions, 

 but oxidizing enzymes also occur, in plants as well as in animals. Laccase was 

 the first of these oxidases to be discovered. It causes the formation of laccol 

 in the latex of various species of Rhus. The latex, which is originally white, 

 changes very quickly in the presence of air and becomes black. Laccase is 

 soluble in water and may be precipitated with alcohol. Its oxidizing effect 

 disappears after heating to ioo°C. Laccase oxidizes various aromatic com- 

 pounds by means of molecular oxygen. The presence of this enzyme is shown 

 by a blue color-reaction with a solution of gum guaiac in 60 to 80 per cent, 

 alcohol. 



1 Neumeister, 1894. [See note 1, p. 159-1 



- Butkewitsch, Wl., Ueber das Vorkommen eines proteolytischen Enzymes in gekeimten Samen und 

 iiber seine Wirkung. Zeitsch. physiol. Chem. 32: 1-53- 1901. 



3 Nicloux, Maurice, Contribution a l'etude de la saponification des corps gras. Paris, 1906. 



* Hoyer, E., Ueber fermentative Fettspaltung (2te Mittheilung.) Ber. Deutsch. Chem. Ges. 37 7/ : 

 1436-1447. 1904. Idem, same title. Zeitsch. physiol. Chem. 50: 414-435. 1906-1907. 



h Sinigrin is potassium myronate, a glucoside, myronic acid being C10H17O9NS2. The 

 hydrolysis is represented by the equation: 



Monopotassium 

 Potassium myronate Glucose sulphate Allyl isothiocyanate 



CioHi6K0 9 NS,+ H 2 = C 6 H 18 0« + KHS0 4 + CH. = CHCH 2 NCS— Ed. 



