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1»201 AGWCULTtTRAL CHEMISTRY — AGROTECHNY. 611 



Isomerism botwooii ;iii aldose and a ketose, resulting in different conditions of 

 oxidation and reduction operating on the intermediate products of the fermenta- 

 tion. The dilhculty with which mannose is fermented is also thought to be due 

 to its configuration. 



The influence of hydrogen-ion concentration on the inactivation of pep- 

 sin solutions, J. H. Noktiikop (Jour. Gen. I'hysioL, 2 (0)20), No. 5, pp. 405- 

 470, figs. 2). — In continuation of the studies on pepsin previously noted (E. S. 

 R., 42, p. 204) the results are reported of a study of the effect of the H-ion 

 concentration, the anion of the acids, and the purity of enzym solution on the 

 activation of pepsin in solution. 



It was found that pepsin in solution at 38° C. was most stable at an H-ion 

 conctMitration of about pH 5. Increasing the H-ion concentration above this 

 value caused a slow increase, and decreasing it a very rapid decrease in the rate 

 of destruction of the enzym. 



The purity of the enzym solution and the anion of the acid used appeared 

 to have no marked effect on the rate of destruction of the enzym or on the 

 zone of H-ion concentration in which it was most .stable. 



" The existence of an optimum range of H-ion concentration for the digestion 

 of proteins by pepsin can not be explained by the destruction of the enzym by 

 either too weak or too strong acid." 



The effect of the concentration of enzym on the rate of digestion of 

 proteins by pepsin, J. H. Northrop {Jour. Gen. Physiol., 2 (1920), No. 5, pp. 

 471-498, figs. 5). — This paper discusses the kinetics of enzym action as applied 

 to the rate of digestion of proteins by pepsin under different conditions de- 

 termined, according to the method previously noted (E. S. R., 42, p. 204), by 

 means of changes in the conductivity of an egg albumin solution to which the 

 pepsin had been added. The conclusions drawn from this study may be 

 sunmiarized as follows : 



In certain cases the rate of digestion of proteins by pepsin is not pro- 

 portional to the total concentration of the pepsin. It is suggested that this 

 is due to the fact that the enzym in solution is in equilibrium with another 

 substance (called peptone for convenience) according to the law of mass action. 

 Pepsin inactivated with alkali apparently enters the equilibrium to the same 

 extent as active pepsin in spite of the fact that it has lost its power to 

 liydrolyze protein. If the concentration of peptone is large with respect to 

 pepsin and the concentration of substrate relatively constant, the relative 

 change in the amount of active pepsin is inversely proportional to the con- 

 centration of the pepsin. 



An integral equation has been obtained which holds for the entire course 

 of the digestion (except for the first few minutes) with varying enzym con- 

 centration. 



The nature of enzym action, W. M. Bayliss {New York and London: Long- 

 mans, Green & Co., 1919, .4. rerv. ed., pp. Vni-\-190, figs. 9). — This is the fourth 

 revised edition of this well-known monograph (E. S. R., 32, p. 19). 



A weight burette for gas analysis, E. R. Weaver and P. G. Lediq {Jour. 

 Amer. Chem. Soc., 42 {1920), No. 6, pp. 1177-1185, figs. 2).— "An apparatus for 

 conveniently determining small quantities of gas by weighing the confining 

 liquid displaced is described, and its percentage accuracy is shown to be com- 

 parable with the general accuracy of good titrimetric measurements." 



A modified form of the Smith fermentation tube, A. V. Fuller {Jour. 

 Indus, and Engin. Chem., 12 {1920), No. 6, p. 595, fig. i).— In the modified fer- 

 mentation tube described the bulb, instead of being symmetrical, is made 

 trough shaped on its under side. This is considered to facilitate the falling of 

 growth to the lowest part of the gas tube proper, with the result that as the 



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