December 7. 1899J 



NA TURE 



41 



It would appear that the natural glucosides, which are for the 

 most part phenol derivatives, probably belong to the group of 

 j8-glucosides. The indifference of some of these glucose 

 derivatives to both enzymes is at present unexplained. 



Configuration and Zyntolyns of the Polysaccharoses. — The 

 recent researches of E. Fischer on the hydrolysis of the poly- 

 saccharoses point to the fact that none of these carbohydrates is 

 directly fermentable by the enzyme of yeast, but that without 

 exception they first undergo hydrolysis by a hydrolytic enzyme 

 associated with the ferment. The di-saccharoses — cane sugar, 

 maltose, milk sugar, melibiose, trehalose, &c. — are anhydrides 

 formed by the union of two hexoses. The structural formulDe 

 of maltose and lactose are probably identical, seeing that each 

 splits up on hydrolysis into two molecules of aldohexose, but 

 since maltose yields only glucose, whereas lactose forms an equal 

 number of molecules of glucose and galactose, the two com- 

 pounds must be regarded as stereoisomeric. They probably 

 correspond, too, with the o-methyl- and'jS-methyl-dextroglucoside, 

 for emulsin hydrolyses lactose, but not maltose ; whereas the 

 enzyme of yeast produces the reverse effect. 



Without discussing in detail the ingenious methods by which 

 Prof. Fischer has successfully attacked the problem of the 

 hydrolysis of the polysaccharoses, the following results may be 

 briefly recorded. 



The action of invertase, an enzyme which accompanies beer 

 yeast, in hydrolysing cane sugar into glucose and fructose 

 previous to fermentation, was first observed by O'Sullivan, and 

 although Bourquelot and Lintner recorded a similar decompo- 

 sition in the case of maltose, the experiments were not decisive. 

 Fischer, however, extracted with water from dry yeast an 

 enzyme which, unlike invertase, hydrolyses maltose, and which 

 he has therefore named maltase of yeast. Instead of the 

 aqueous extract, the dry yeast itself may be employed ; in which 

 case a little toluene must be added to the maltose solution to 

 arrest the alcoholic fermentation. 



The conclusion may be drawn that yeasts incapable of inducing 

 alcoholic fermentation of cane sugar and maltose are destitute 

 of invertase and maltase. This conclusion has been fully cor- 

 roborated by subsequent experience. 



Kephir grains and the yeast which ferments milk sugar do 

 not ferment maltose, and are also without hydrolytic action 

 upon it. 



Saccharomyces inartianiis, which according to Hansen does 

 not ferment maltose, does not hydrolyse it, and is therefore free 

 from maltase. 'Qeyennck' s Schizosaccharontyces octosporus, which 

 acts on maltose but is indifferent to cane sugar, contains maltase 

 but no invertase. Monilia Candida is a particularly interesting 

 case, since it contains neither invertase nor maltase, but never- 

 theless produces fermentation ot both cane sugar and maltose. 

 No aqueous extract which hydrolyses these two sugars could be 

 obtained from it, but if the dried yeast is added to a solution of 

 cane sugar in presence of toluene a vigorous hydrolysis is pro- 

 duced. The hydrolytic enzyme is present, but in this case it is 

 in.soluble in water. 



Milk sugar, which is not attacked by beer yeast, is fermented 

 by kephir grains and milk sugar yeast, which Beyerinck sus- 

 pected to contain the hydrolytic enzyme lactase. The existence 

 of this enzyme has been placed beyond question by Fischer, 

 who has prepared the enzyme from kephir grains and milk sugar 

 yeast in the dry state. It is accompanied by invertase, but 

 maltase is entirely absent, and indeed no substance is yet known 

 in which maltase and lactase are associated. 



I The hydrolysis of trehalose by an enzyme contained in Asper- 

 gillus niger and in green majt was observed by Bourquelot, and 

 has since been confirmed by Fischer, who found also that a 

 Frohberg dry yeast affected a similar but much more feeble 

 decomposition. 



Melibiose, which is a disaccharose, is obtained from raffinose. 

 It is fermented by a ^ow fermentation brewer's yeast. Fischer 

 and Lindner have now been able to prove the existence in this 

 yeast of a hydrolytic enzyme which they call melibiase. 



In regard to the action of different yeasts on o-methyjgiuco- 

 side and its congeners, Fischer has shown that all yeasts which 

 ferment maltose attack the a-methyl glucoside. The question 

 then arises, has each glucoside or polysaccharose its special 

 enzyme and each fermentable sugar its special ferment or 

 zymase ? Fischer considers such a proposition untenable, but 

 inclines to the view that one and the same enzyme of yeast, 

 maltase, attacks o-methyl glucoside as well as melibio.se and the 

 complex carbohydrates known as dextrins. 



Theoretical considerations. — All these facts indicate that the 

 chemical action of enzymes, in which may be included the 

 zymase of yeast, is of quite a special character and distinct frc m 

 that of the more simple organic and inorganic compounds. The 

 cause of this selective action probably resides in the asymmetrical 

 structure of the enzyme molecule. Although these substances are 

 not yet known in the pure state, their relation to the proteids is 

 so close and their derivation from the latter so probable, that they, 

 may be regarded as optically active molecular aggregates, and 

 consequently asymmetrical. Fischer and Thierfelder have basecfc 

 upon this the hypothesis that between the enzymes and those 

 substances which they attack, there must exist a correspondence 

 in molecular configuration, which they compare to a lock and- 

 key. The observations of G. Bertrand on the relation of the 

 polyvalent alcohols to their oxidisability by the sorbose bacteria, 

 shows clearly that stereochemical considerations may be applied 

 to other fermentive processes. Fischer applies the same idea to 

 the chemical changes occurring in the bodies of higher organisnT;, 

 which lead to the conclusion that in the chemical changes in which 

 the proteid substances take a part as active masses, undoubtedly 

 the case with protoplasm, the configuration of the molecule [i.e. 

 space arrangement of the atoms) plays a part fully as impoi tant as 

 its structure [i.e. plane, or relative arrangement of the atoms). 

 It is easy to conceive on this hypothesis that the three isomeric 

 tartaric acids should be assimilated at an unequal rate in the- 

 organism of the dog, and that of two sugars so closely allied as 

 glucose and xylose, it is only the former which is oxidised or 

 converted into glycogen, whereas xylose passes unaltered 

 through the system. 



The results of stereochemistry may also throw some light on 

 chemical transformations occurring in the organism. The four 

 sugars, (/-glucose, (/-mannose, af-fructose and ^/-galactose are 

 not only those that are exclusively attacked by yeast, but these 

 which in the animal system are assimilated as glycogen. The 

 conversion of glucose, mannose and fructose into one another 

 was first achieved by Fischer by a process of alternate reduction 

 and oxidation, since when Lobry de Bruyn and van Ekenstein 

 have arrived at the same result by simply warming with 

 alkalis. 



As von Baeyer pointed out twenty-eight years ago, all 

 these phenomena may be explained by the intramolecular 

 migration of an oxygen atom from one carbon atom to the other.. 

 The intermediate phases of this process are unknown ; but 

 alcoholic fermentation is an example of the facility with which 

 the operation is effected. In regard to the assimilation of carbon 

 dioxide by plants, which gives rise to exclusively active sugars, a 

 similar explanation may be found, seeing that the carbon dioxide 

 in process of assimilation is associated with the optically active 

 chlorophyll bodies. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge.— Mr. F. C. Kempson, of Caius College, has 

 been reappointed a Demonstrator of Anatomy for one year ; 

 and Dr. Elliot-Smith, Fellow of St. John's College, a Demon^ 

 strator of Anatomy for five years. 



The work of Mr. W. Rosenhain, advanced student of St. 

 John's College, which includes the joint Bakerian Lectures, 

 with Prof. Ewing, delivered this year, has been approved for 

 the University certificate of research. 



Dr. Hill, Dr. Allbutt, Dr. Sladen, and Prof. Woodhead have 



NO. I 57 I, VOL. 61] 



