Feb. is. 1921 Amylase of Rhizopus tritici 783 



ing period. So far as the writer is aware, this fact has not been deter- 

 mined for Rhizopus tritici, and it was with the view of verifying it for 

 this fungus alone that comparative tests were made. In the experi- 

 ments carried out by the writer two different culture media were used — 

 namely, sweet potato bouillon and a modification of Czapek's nutrient 

 solution with a 0.5 per cent starch paste as a source of carbon. In the 

 former case the mycelium was removed from one set of flasks 3 days 

 after inoculation, when fruiting was just beginning. The mycelium was 

 removed from the other set of flasks 10 days after inoculation. The 

 difference in reducing power in this case was not large. 



On the other hand, when the Czapek 's modified solution was employed, 

 the mycelium removed 5 days after inoculation (when just beginning to 

 fruit) hydrolyzed considerably more starch in a given length of time 

 than the mycelium removed 10 days later. 



SUMMARY 



(1) A vigorous starch-splitting enzym is secreted by Rhizopus tritici. 

 While some of the enzym is retained in the mycelium of the fungus, a 

 portion of it diffuses out into the substratum. The diffusion into the 

 culture medium begins soon after the substratum is inoculated, as was 

 shown by some of the experiments in which reducing sugars appeared 

 after 2 days in a nutrient solution with starch as the only source of car- 

 bon. The reducing sugars in such a medium accumulate in excess of the 

 needs of the fungus. 



(2) The enzym is able to act on raw sweet potato and Irish potato 

 starch but much less energetically than on starch paste. 



(3) The dried mycelium may be stored for several months at a tempera- 

 ture of from 9 to 35 ° C. without much deterioration, but at 6o° it grad- 

 ually becomes weaker. 



(4) The optimum temperature for the digestion of starch is about 

 45 C. Above and below this temperature the amount of hydrolysis 

 becomes less, and at 6o° it is completely destroyed in 100 hours. 



(5) If glucose is added to a system the hydrolysis of starch paste is 

 retarded. The quantity of glucose added does not seem to influence the 

 results. With a constant amount of enzym powder the total reducing 

 sugars formed in a solution of starch paste increases with the increase in 

 the volume of the solution up to a certain point and then decreases. 



(6) An end point in the hydrolysis of the starch is not reached without 

 altering the equilibrium of the system. This was done by changing the 

 temperature and diluting the solution. If judged by the iodin test an 

 end point was obtained, but a quantitative determination of the reducing 

 sugars did not account for all the starch. It is probable that in this case 

 some of the products of the hydrolysis were dextrins which were not ac- 

 counted for as either starch or reducing sugars. 



