ENZYMES 505 



the production of diastase to a slight extent 1 , and since the accumulation of the 

 fermentative products ultimately inhibits further action, the fact that the solution of 

 starch is hastened by the continual removal of the sugar produced, affords no 

 evidence to show that the formation of diastase is subject to regulatory modifi- 

 cation. Enzymatic action may be affected by the acid or alkaline reaction of the 

 medium as well as by the presence of various substances, and hence by these 

 means alone the plant is able to regulate the activity of ferment-substances 2 . 

 Pepsin works only in an acid, trypsin only in an alkaline solution, and hence when 

 both are mixed together one only can be active. In other cases, however, two or 

 more enzymes may act simultaneously, and even proteolytic enzymes apparently 

 exert only a slight destructive influence upon other enzymes s . 



Temperature. Most enzymes are destroyed at a temperature lying between 

 60 and 70 C., but those which are produced by thermophilous bacteria are 

 probably more resistant 4 , and the character of the medium as well as the presence 

 of certain substances may raise or lower the maximal temperature. Every en- 

 zymatic action must therefore attain an optimum at a certain temperature, beyond 

 which the fermentative activity decreases until the point is reached at which the 

 ferment is destroyed. Details are given in the works already quoted of Ad. Mayer, 

 A. Meyer, Schleichert, Fliigge, &c. For an account of the inhibitory action of 

 strong light see Green, Annals of Botany, 1893, Vol. vn, p. 372; Phil. Trans., 

 1897, Vol. CXLIV, p. 167; Fermi, I.e., 1894, Bd. xvi, p. 830; Linz, Jahrb. f. wiss. 

 Bot., 1896, Bd. xxix, p. 279. 



Methods. The fermentative action of an enzyme is usually employed as a test for 

 its presence, as is also the case in Beyerinck's method of using the physiological 

 reaction of luminous bacteria as an indication of fermentative activity. Griiss has 

 recently employed the blue colouration given by guiacum and hydroxyl as a test 

 for the presence of diastase, but the method requires careful control, and, according 

 to Jacobson, various agencies may suppress the guiacum reaction without destroying 

 the diastatic action 5 . 



Diastases or amylohydrolytic ferments are very widely distributed, and in spite 

 of a few negative results every plant may have the power of producing some form or 

 other of diastase. It is, however, uncertain whether the presence and solution of 

 starch necessarily involves a power of secreting diastase, but the latter may be 

 detected in the most widely different plants or parts of plants either always or only 

 at certain stages of development. Thus diastase may be present in both young 



1 Literature: Brown u. Morris, Bot. Zeitung, 1892, p. 464; Griiss, Landw. Jahrb., 1896, Bd. 

 xxv, p. 442. 



2 Literature : Ad. Mayer, Die chem. Fermente", 1882, p. 78 ; Schleichert, 1. c., p. 69; A. Meyer, 

 Starkekorner, 1895, p. 67; Fliigge, I.e., p. 213. According to Bertrand (Compt. rend., 1897, T. 

 cxxiv, p. 1032), laccase acts only in the presence of manganese. 



3 Ad. Mayer, I.e., p. 97; Fermi, Centralbl. f. Bact., 1894, Bd. xv, p. 234. On self-digestion, 

 cf. Sect. 78. 



* [On the proteolytic enzyme of Nepenthes, cf. Vines, Annals of Botany, xi, Dec., 1897, p. 583.] 

 5 Beyerinck, Centralbl. f. Bact., 1895, Abth. ii, Bd. I, p. 222; Griiss, Ber. d. Bot. Ges., 1895, 



p. 2 ; Landw. Jahrb., 1896, Bd. xxv, p. 385 ; Jacobson, Zeitschr. f. physiol. Chemie, 1892, Bd. xv, 



p. 340; Pawlewski, Ber. d. Chem. Ges., 1897, p. 1313. 



