. Carnegie Institution of Washington publication. ENZYMES. 67 first be reduced to glucose (grape-sugar), before they can be used as food by plants. When no invertase has been detected the general hypothesis has been that this inversion was due to the direct action of the protoplasm, but the recent isolation by Buchner and others of an invertase (Zymase) from yeast, in which it was long believed that none existed, once more emphasizes the uncertainty of negative conclusions. Diastase is common. Is there more than one kind, i. c., a sort which can only convert the starch into amylodextrin and an
. Carnegie Institution of Washington publication. ENZYMES. 67 first be reduced to glucose (grape-sugar), before they can be used as food by plants. When no invertase has been detected the general hypothesis has been that this inversion was due to the direct action of the protoplasm, but the recent isolation by Buchner and others of an invertase (Zymase) from yeast, in which it was long believed that none existed, once more emphasizes the uncertainty of negative conclusions. Diastase is common. Is there more than one kind, i. c., a sort which can only convert the starch into amylodextrin and another which converts it into maltose and dextrine ? In many cases, when the organism is grown on potato, the con- version is carried only a little way and stops, there being always a copious purple or red-purple reaction with iodine. In other cases, , when Bacterium campestre is grown on potato, the starch conversion is so complete that after a few weeks there is little or no color reaction when the potato-cylinder is mashed up and iodine water added. What makes this difference? A substance capable of dissolving the middle lamella appears to be common to all bacterial plant parasites and a true cytase presumably occurs, but much additional study is necessary. Probably several enzymes are confused under this name, just as several chemically different substances are still called " ; The substance which dissolves the middle lamella in some cases is prob- ably ammonium oxalate. The writer has not been able to dissolve it by means of pure oxalic acid, but that of turnips softens in ammonium oxalate. The lab or rennet ferment is rather common. Its action should not be confused with the curdling of milk due to the formation of acids. Tests may be made in litmus milk. Is there more than one kind of such ferment? Some organisms coagu- late the milk promptly into a solid mass which finally shrinks, extruding whey. Others cause the Fig- 58,* casein to separate out
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