114 Journal of A gricultural Research voi. v, no. 3 



cooled, and made to its original volume; and to the third, 5 c. c. of dis- 

 tilled water. Another set of three test tubes was prepared with the same 

 proportions of materials, but using a i per cent solution of Witte's peptone 

 in place of the albumin solution. The tubes so prepared were kept in an 

 incubator at 40° C. for 24 hours. At the end of this time an aliquot of 

 each mixture was drawn off and the quantity of amino acids present in it 

 determined by the ninhydrin method recently proposed by Harding and 

 Maclvcan (7) , using a solution of glutamic acid containing the equivalent 

 of o. I mgm. of nitrogen in the amino-acid form per cubic centimeter for 

 the production of the standard color. 



The characteristic color due to amino acids appeared in all the tests 

 except the one in which only water and albumin were used. The amino- 

 acid equivalent in each case, as determined by comparison with the stand- 

 ard color, is given in Table VII. 



Table VII. — Tests for proteases in the flesh of apples 



Amino-acid 

 equivalent after 

 action (milli- 

 grams of ni- 

 trogen). 



Unboiled juice + egg albumin 

 Boiled juice -f egg albumin . . . 



Water -f egg albumin 



Unboiled juice + peptone 



Boiled juice + peptone 



Water + peptone 



O. 13 



.07 



None. 

 . 10 

 . 10 

 •03 



It appears from these data that both the juice itself and the peptone 

 used contained amino acids which would give a blue color with the nin- 

 hydrin reagent. But the incubated mixture of unboiled juice and albu- 

 men contained more amino acids than that in which an equal volume of 

 boiled j nice was used ; while with peptone no increase of amino acid was pro- 

 duced by the unboiled juice, and the total amino acid found was just equal 

 to the sum of that found in the quantity of juice and of peptone solution 

 used in the tests. It thus appears that the juice extracted by grinding 

 with quartz sand contains a small amount of some protein-splitting 

 enzym of the trypsin or papain type rather than of the erepsin type. It 

 was concluded, therefore, that the flesh of the apples contains a small 

 amount of protease, to the action of which on the protein material of the 

 apple cells is due the small amount of amino acid found to be present in 

 the juice of the ripening fruit. 



PECTINASES 



The fact that the flesh of an apple softens and becomes mealy or mushy 

 at the close of the ripening period is generally attributed to the solution 

 of the middle lamella and the consequent separation of the cells of the 

 tissues. The solution of the middle lamella is supposed to be the work 

 of an enzym known as pectinase. It is supposed, therefore, that pecti- 



