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 ioo°C. 
and most of them cannot be heated safely above 6o°C. 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. 
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CLASSIFICATION OF ENZYMES 
A. According to Di{fusibility 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 oryzce , 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. 
