VEGETABLE CYTOLOGY 95 



differ from the inorganic catalysts in that they are sensitive to heat 

 and light. According to Haas and Hill they are destroyed at iooC. 

 and most of them cannot be heated safely above 6oC. Enzymes 

 are soluble in water, glycerin or dilute saline solutions. They are 

 stimulated to activity by substances known as "activators" and their 

 activity is checked by other substances called " paralyzers ." Fre- 

 quently the paralyzers consist of products of enzyme action. Cold 

 inhibits and warmth accelerates enzyme action. Moisture must 

 always be present for enzymic activity. 



CLASSIFICATION OF ENZYMES 



A. According to Di/usibility through Cell Wall. 



Endocellular : Those that cannot diffuse out of the cell. Example : 

 Zymase of Yeast. 



Extracellular: Those that can diffuse out of the cell. Example: 

 Invertase of Yeast. 



B. According to Kind of Substances Acted upon and Transformed. 

 i. Carbohydrate enzymes: 



Diatase found in the germinating seeds of barley and 

 other grains and in Aspergillus oryza, etc., converts starch to 

 maltose and dextrin. 



Invertase, secreted by yeasts, and found in younger parts 

 of higher plants, transforms cane sugar, producing dextrose and 

 levulose. 



Maltase, found in malt and Saccharomyces octosporus, transforms 

 maltose to dextrose. 



Trehalase, found in Polyporus, hydrolyzes trehalose to dextrose. 



Cytase, found in Nux Vomica seeds, in barley, dates, etc., decom- 

 poses hemicellulose and cellulose to galactose and mannose. 



Lactase, found in Kephir grains, hydrolyzes lactose to dextrose 

 and galactose. 



Inulase, found in Compositaceous plants, transforms inulin to 

 levulose. 



Zymase, found in yeast, hydrolyzes glucose (dextrose and levu- 

 lose) to alcohol and carbon dioxide. 



