IX] GLUCOSIDE-SPLITTING ENZYMES 149 



MUSTARD-OIL GlUCOSIDES. 



These are glucosides containing sulphur and they have been found 

 chiefly among the Cruciferae. Sinigrin and sinalbin, the glucosides of 

 mustard, have been most investigated. 



Sinigrin. This glucoside occurs in the seed of Black Mustard 

 (Brassica nigra) and other species of Br-assica. Also in the root of the 

 Horse-radish (Cochlearia Armoracia). Sinigrin is hydrolyzed by the 

 enzyme, myrosin (Guignard, 16; Spatzier, 18) (which occurs in the 

 plant together with the glucoside), into allyl isothiocj^anate, potassium 

 hydrogen sulphate and glucose: 



CioHigOyNSaK + H.O = C.HgNCS + C«Hi.p,; + KHSO^ 



Expt. 145. Extraction of sinigrin from Black Mustard. Weigh out 100 gms. of 

 Black Mustard seed. Grind the seed in a coffee-mill and afterwards pound in a 

 mortar. Heat 175 c.c. of 85 "/q alcohol to boiling in a flask on a water-bath and add 

 the pounded mustard, and after boiling about h hour, filter and press out the alcohol. 

 Then put the dried cake of residue into 300 c.c. of water and allow the mixture to 

 stand for 12 hours. Press out the liquid and after filtering and neutralizing with 

 barium carbonate, concentrate in vacuo to a syrup. Then extract with 90% alcohol 

 and filter. On concentrating and exposing in a crystallizing dish, the sinigrin 

 separates out in white needles. 



Sinalbin occurs in the seeds of White Mustard {Sinapis alba). By 

 myrosin it is hydrolyzed to j9-hydroxybenzylisothiocyanate, acid sinapin 

 sulphate and glucose: 



C.oH4.,OigN2S,, + H2O = CgHiaOe + C-H^ONCS + C,^H..05NHS04 



Expt. 146. Extraction of sinalbin from White Mustard. Weigh out 100 gms. of 

 White Mustard seed. Grind and pound well and extract the fat with ether. Then 

 extract with twice its weight of 85-90 "/o alcohol several times and well press out the 

 alcohol. The extract is evaporated to half its bulk and filtered. On cooling the 

 sinalbin separates out in crystals. 



Expt. 147. Preparation of myrosin. Weigh out 50 gms. of White Mustard seed and 

 grind in a cofFee-mill. Add 100 c.c. of water and allow the mixture to stand for 

 12 hours. Then filter and allow the filtrate to run into 200 c.c. of 95-98 o/^ alcohol. 

 A white precipitate is formed which contains the myrosin. Filter oft' the precipitate 

 and wash on the filter with a little ether. 



Expt. 148. Action of myrosin on sinigrin. Put into two test-tubes equal quantities 

 of a solution of the sinigrin prepared in Expt. 145. Dissolve some of the myrosin 

 prepared in the last experiment in water and divide the solution into two parts. 

 Heat one part to boiling and then add the two portions respectively to the two test- 

 tubes of sinigrin. Plug both test-tubes with cotton-wool. After about h hour a 

 strong pungent smell of mustard oil, allyl isothiocyanate, will be detected in the 

 unboiled tube. 



A more simple method of demonstrating the action of myrosin is as follows. 



