Page 8 - ALLEN'S COMMERCIAL ORGANIC ANALYSIS A TREATISE ON THE PROPERTIES, MODES OF ASSAYING... VOL VIII

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4 ENZYMES
obtain the optimum activity of the enzyme. The results so obtained 0
were about twenty times as high as when no electrolyte was added. \
Their procedure is as follows: pure soluble starch and water are
used at 4o; o.3 grm. of sodium chloride and 7 c.c. of N] 5 disodium
phosphate are added per roo c.c. of reaction mixture. roo c.c. of 2%
soluble starch are digested with the enzyme solution for exactly go
minutes. •
All the vessels and solutions are preheated at 4o°. Several experi-
ments may be started simultaneously with varying proportions of
enzyme. At the expiration of the time soc.c, of Fehling's solution is
added, the flask immersed in a bath of boiling water for 10 minutes
and the reduced copper determined by any of the usual methods,
The weight of cuprous oxide must not exceed goo mg.; it is corrected •
by the value found in a blank without the enzyme.
By plotting the velocity curve of diastatic action, which is not a
straight line, with time as abscissre and yield of reducing sugar as
ordinates, a scale is obtained which permits of an expression of true
diastatic power based on the weight of cuprous oxide obtained.
30o mg. of cuprous oxide is taken as roo on this scale and the
corresponding scale values of K are given in the following table.

Cuprous Cuprous Cuprous Cuprous
oxide I I oxide I oxide oxide
Mg. K Ms. K Ms. K Mg. K
30 9.1 I0o .% 10 $4.F a40 178.4
31.2
40 12.5 to 180 $7.5 250 81.8
so 15.3 1o I9o 60.9 260 85.4
60 18.4 30 40 9 200 64.3 270 89.0
70 21.6 4o 44. 21o 61.8 280 92.6
8o 24.8 1so 47.5 220 7 3 290 96.3
90 28.0 16o so 8 a30 74.8 30o 100.0
The values of K are divided by the respective weights of enzyme.
When any other time is used the standard time, 3o minutes, is divided
by the actual time in minutes and multiplied by the value of K. Thus
in 3o minutes 0.15, 0.30, 0.45, 0.6o mg. of pancreatin yielded respec-
tively 76, 147, 217, 286 mg. of cuprous oxide, whence K= 23.5, 46.5,
70.2 and 94.8; then the diastatic power is 156, 155, 156, 158 units.°

Iodine Methods.
Robert's Method (Proc. Roy. Soc., 1881, 32, 145). -In this the
time taken at 4o°to convert a 1starch solution into achroodextrin, the
first point at which no colour is given by iodine solution, is measured. •
The acceleration is more probably due to the effect of the acid phosphate in neutralis-
ing alkaline impurities,
+See Appendix.