MALTASE 481 



destroyed at 55*^ C. Its optimum reaction is Pg 6-8,* but 

 this would appear to vary, for Pringsheim and Leibowitz has 

 described a maltase from barley whose optimum reaction is 



Ph 4-5-5-o.t 



PREPARATION. 



In view of the instability of maltase, its preparation cannot 

 follow the ordinary course ; active preparations are obtained 

 by extracting dried yeast with water, the rate of extraction 

 being increased with a rise in temperature ; a low temperature, 

 15° C, is, however, preferable since the destruction of enzyme 

 is less. The reaction should be neutral. If fresh yeast be 

 used, the amount of maltase obtained is less and the best 

 temperature to use is 30° C.| Willstatter and Bamann § 

 autolysed yeast with ethyl acetate, keeping the reaction 

 neutral and the temperature low. The enzyme may be separ- 

 ated from the filtered extract by adsorption on alumina, from 

 which it can be recovered by ammonium phosphate. 



PROTEOLYTIC ENZYMES. 



OCCURRENCE. 



The proteolytic enzymes of plants fall into three main 

 groups: protease, II which hydroylses protein to albumins and 

 peptones ; peptidase (erepsin), which hydrolyses albumins and 

 peptones into amino acids such as leucine and tyrosine ; and 

 amidase, which hydrolyses amino acids to ammonia. 



Protease when present in the plant is usually associated 

 with peptidase (erepsin) ; Drosera ^ provides one of the few 

 examples in which it occurs alone. Even where proteases 

 might be expected, in protein containing seeds for example, 

 they may be wanting. Dean's work on Phaseolus vulgaris 

 may be taken as an example.** The seeds of this plant 



* Willstatter, Kuhn, and Sobotka ; " Zeit. physiol. Chem.," 1924, 134, 

 224. 



I Pringsheim and Leibowitz : " Biochem. Zeit.," 1925, l6l, 456. 



X Krieble, Skaw, and Lovering: " J. Amer. Chem. Soc.," 1927, 49, 1728. 

 § Willstatter and Bamann: "Zeit. physiol. Chem.," 1926, 151, 242, 



273- 



II Vines : " Ann. Bot.," 1905, 19, 171 ; 1908, 22, 103. 



il White : " Proc. Roy. Soc. Lond.," B., 1910, 83, 134. 

 ** Dean : " Bot. Gaz.," 1905, 39, 321. 



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