126 THE CARBOHYDRATES 



to the presence of a substance known as pectose, which is 

 deposited in the cell walls ; as the fruit ripens the pectose 

 undergoes a variety of changes, and is ultimately converted 

 into pectin. 



Under the action of an enzyme pectase contained in the 

 plant, pectin is coagulated ; this change was first studied by 

 Fremy, and later by Bourquelot and Herissey ; * according to 

 Duclauxf and others, the coagulation is dependent on the 

 presence of calcium salts, and will take place even in the 

 absence of the enzyme. 



Comparatively little is known about the chemistry of pec- 

 tin or the pectic bodies, as there appear to be several of these 

 substances ; at one time there was even some doubt as to 

 whether they were really carbohydrates, since the ratio of 

 hydrogen to oxygen seemed to be less than that required for 

 compounds belonging to this group. Analyses by Tromp de 

 Haas and Tollens,:J: however, agree fairly well either for the 

 formula (C,H,„0,)„ or 2C,H,,0, . H,0. 



By boiling pectose with dilute acids or caustic alkalis, a 

 number of different substances are produced, such as pectin, 

 parapectin, metapectin, pectic acid — which is combined with 

 bases, such as calcium, and forms the middle lamella of cell 

 walls — parapectic acid and parapectosic acid, some of which 

 are soluble in water, while others, such as pectin, swell up in 

 water and gelatinize. The final product of these changes, 

 namely, metapectic acid, is readily soluble in water ; it would 

 appear to be closely related to, or identical with, arabane, and 

 on hydrolysis with dilute sulphuric acid gives arabinose. 



This view receives confirmation from the work of Bour- 

 quelot and Herissey, who have discovered an enzyme occurring 

 in malt, which is not identical with diastase, and which is 

 capable of hydrolysing pectose to a reducing sugar, namely, 

 arabinose. This enzyme, to which they gave the name pec- 

 tinase, acts both on unaltered and on coagulated pectic bodies, 

 but, conversely, the coagulating enzyme pectase is without 



* Bourquelot and Herissey: " J. Pharm. et Chim.," 1898, [6], 8, 145 ; 1899, 

 [6], 9. 563, and 10, 5- 



t Duclaux : " Traite de Microbiologie," 1899, 11, 336, and Goyaud : " Compt. 

 rend.," 1902, 135, 537. 



X Tromp de Haas and Tollens : " Annalen," 1895, 286, 278. 



