600 VEGETABLE ENZYMES. XIX 



A number of experiments were carried out in which the treated 

 pulp was centrifuged and the supernatant liquid dialyzed and used, 

 or where the treated pulp was squeezed through muslin and then 

 centrifuged. The properties of the sucrase solutions so obtained 

 were essentially the same, but the above procedure was the one 

 finally adopted for studying the soluble banana sucrase. 



The following methods of extraction did not yield preparations so 

 satisfactory as the salt treatment described : Extraction with one- 

 fourth weight or equal weight of water (fairly active preparations, 

 in one case 2| times as much action was obtained by the salt extrac- 

 tion as by the water extraction); extraction of small portions of 

 banana with ten times the weight of water or salt solution; autolysis, 

 followed by filtration, etc., as in the preparation of yeast sucrase^ 

 (slightly active filtrate obtained); and grinding in a ball mill for a 

 long period of time (inactive filtrate). 



It may be mentioned that repeated extractions did not offer any 

 appreciable advantage over a single treatment. A small amount of 

 active material could be obtained on a second extraction as com- 

 pared with the first extract. Extracting for longer periods of time 

 did not give appreciably more active solutions. 



The following results were obtained in testing at different hydrogen 

 ion concentrations. 10 cc. of the salt-extracted dialyzed solution plus 

 10 cc. of a 20 per cent sucrase solution were incubated for 2| hours 

 at 35°C. The actions are given in terms of mg. of CU2O produced 

 by the action of 1.0 cc. of original undialyzed filtrate corrected for 

 blanks. 



pH 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 



Actions 183 481 489 478 458 375 135 52 



Fig. 1 shows these results graphically. There is a zone of maximum 

 action between pH 3.5 and 4.5, with rapid drops beginning between 3.5 

 and 3.0 and at 5.0. This optimum zone corresponds to that observed 

 with yeast sucrase solutions, where the zone is of different widths 

 in various experiments and under different conditions,^" and with 



^ Nelson, J. M., and Born, S., /. Am. Chem. Soc, 1914, xxxvi, 393. 

 1" Sorensen, S. P. L., Blochem. Z., 1909, xxi, 131. Michaelis, L., and David- 

 sohn, H., Biochem. Z., 1911, xxxv, 386. Fales, H. A., and Nelson, J. M., /. Am. 

 Chem. Soc, 1915, xxxvii, 2769. Michaelis, L., and Rothstein, M., Biochem. Z., 

 1920, ex, 217. 



