4. MAMMALIAN PANCREATIC AND SALIVARY ENZYMES By MARGARET HOLDEN

In other papers ofthis series (Holden, Pirie & Tracey, 1950; Holden, 1950a, b) the effects of a number of polysaccharases on leaf fibre are described. The only polysaccharase recognized in tobacco leaves in significant quantity is amylase (Frankenburg, 1946), and even this is not present in sufficient quantity to effect complete removal of starch on repeated prolonged incubation. It is convenient to remove the leaf starch so that varying amounts of starch hydrolysis by the leaf amylase will not complicate the results observed with other enzymes. This has been done with salivary amylase. Some of the enzyme preparations studied do not contain protease in significant amounts. Trypsin has accordingly been used in the form of a crude preparation from pancreas in order to remove protein. This 'trypsin' contains amylase, and the effect ofthe other enzymes present in it may be made clearer by preliminary treatment of the substrate with salivary amylase. The protease in tobacco-leaf fibre has already been described (Tracey, 1948). The low activities found will be still lower under the conditions used in the present work, for no reducing agents were added and experiments were carried out at pH 7, whereas the pH optimum of the leaf protease is about 5. The effect of tobacco protease can therefore be ignored. Commercial trypsin softens the fibre. This softening is probably due to the protease component of the mixture, for similar effects are obtained by the use of crystalline chymotrypsin (Bawden & Pirie, 1946).