June 9,1923 
Substrate and Hydrogen-Ion Concentration 
869 
pectinase. Although the qualitative regulation of pectinase has been 
demonstrated here for the first time, it is a well-known phenomenon 
for other enzyms. A brief review of some of the literature bearing 
on other enzyms showed that some of them, diastase for instance, are 
produced more abundantly when starch forms the only available source 
of carbohydrates in the solution. 
INFLUENCE OF THE HYDROGEN-ION CONCENTRATION OF THE 
SUBSTRATE ON PECTINASE PRODUCTION 
METHODS OF EXPERIMENTATION 
Two different solutions, sweet-potato decoction and Czapek’s modified 
solution, were used in the investigations of the influence of the hydrogen- 
ion concentration of the substrate on pectinase production. These two 
solutions were employed for two reasons: First, it has proved that 
Rhizopus tritici makes a good growth on both of them; second, they are 
easily prepared and thus available for experimental work at all times. 
The original solutions were prepared in sufficient quantity for a number 
of experiments. In the case of Czapek’s nutrient solution the chemicals 
were put into a large enamel-ware vessel arid the water added. The 
sugar was then added and the mixture heated for about one-half hour. 
A precipitate which formed during the process of heating was removed 
by filtering. The sweet-potato decoction was prepared according to the 
method described on page 862, except that 800 gm. of potato were used for 
each liter of water. From this point on the methods employed were the 
same for both solutions. Both solutions were riiade up to a strength such 
that when 30 cc. were diluted to 50 cc. they were of the desired concen¬ 
tration. The general method for adjusting a solution to a definite hydro¬ 
gen-ion concentration described by Karrer and Webb (13) was employed. 
These authors, using Czapek's solution and beet decoction, worked out a 
method whereby the addition of a definite amount of acid, alkali, or 
water to 30 cc. of the stock preparation would give a definite hydrogen-ion 
concentration. They showed that it was possible to obtain a range of 
Ph 1.2 to 10 + and 1.2 to 9.8 in beet decoction and Czapek’s solution 
respectively by varying the amounts of N/5 HCl and N/5 KOH. The 
writers, selecting out of the series given by Karrer and Webb such Ph 
values as they wished to use, employed their method and made up 
Czapek’s nutrient solution and sweet-potato decoction to these hydrogen- 
ion concentrations. Although the hydrogen-ion concentrations obtained 
were not identical with those obtained by Karrer and Webb, they gave a 
range sufficient to meet all the needs of these experiments. The final 
amount of the solution in each flask was 50 cc. Exactly 30 cc. of the 
stock solution (Czapek’s solution or sweet-potato decoction) were added 
to each flask by means of a self-filling burette. The desired amount of 
water was added and the solutions were then autoclaved for 20 minutes 
at 15 pounds pressure. The required amounts of acid and alkali were 
then added to each flask under aseptic conditions. The burette was first 
sterilized with 95 per cent alcohol and then washed with sterile distilledi 
water. Care was taken at every step to prevent contamination. The 
quantity of acid, alkali, or water to be added to make the solutions up to 
50 cc. depended upon the hydrogen-ion concentration desired. 
The acid and alkali with which the dilutions were made were held in 
two liter flasks. The flasks were plugged with rubber stoppers through 
