Abstract
1. Enzyme preparations from 11 plant sources, from yeast and from the protozoan Tetrahymena pyriformis show nigerase activity, which, in most preparations, was 70-90% of that towards maltose. 2. These enzyme preparations also hydrolysed isomaltose, but there was a wide variation in relative maltase to isomaltase activity. 3. The maltase and nigerase activities of alfalfa and tomato preparations could not be differentiated by heat inactivation or inhibitor methods. However, with turanose used as a competitive inhibitor, evidence suggesting that maltose and nigerose are hydrolysed at different catalytically active sites in the alfalfa preparation was obtained. 4. It is probable that the alfalfa alpha-glucosidase exists as a mixture of isoenzymes.