106 CARBON METABOLISM II 



Fr— Gl + Enzyme (E) ±=; Fr— E + Gl (3) 



Fr— E + Fr— Gl t=; Fr— Fr— Gl + E (4) 



Fr— E + H 2 -> Fr + E (5) 



The fructose-enzyme complex is, of course, hypothetical but it is neces- 

 sary to explain the observed reactions. Because of the irreversibility 

 of the fifth reaction and the great excess of water present, in a long- 

 term experiment virtually all of the fructose residues are transferred 

 to water and the result is described grossly by Equation 2. The 

 technique of paper chromatography applied in short-term experiments 

 has been essential to the elucidation of this type of group transfer. 

 The characteristic of transglycosidase action on disaccharides is the 

 transient appearance of new oligosaccharides. 



Disaccharides. Most of the work on this topic has been concerned 

 with the breakdown of sugars, especially the common disaccharides 

 such as sucrose, maltose, and lactose. Synthesis of disaccharides occurs 

 in the fungi, the best known case being trehalose (p. 108). Sucrose 

 is attacked by an enzyme variously known as invertase, saccharase, 

 glucosaccharase, and sucrase; the name sucrase is preferred. The first 

 indication of its presence in fungi came from the work of Bechamp 

 (18, 19). As might be expected from the frequent utilizability of 

 sucrose as a carbon source (Chapter 3), the enzyme is widely distributed 

 in the fungi. Sucrase is somewhat rare in the Mucorales — again in 

 agreement with nutritional data — but does occur in some species (93, 

 203). Sucrase is found in some isolates of Streptornyces (101, 110), 

 not in any of five species of dermatophytes (229). 



Fungus sucrase may be entirely intracellular (148) but is usually 

 found also in the medium, at least after the onset of autolysis (58). 

 It occurs in spores (71, 141); in Myrothecium verrucaria and Aspergil- 

 lus luchuensis there is evidence that it or a sucrose phosphorylase is 

 located at or near the spore boundary (142). This boundary location 

 is thought to be characteristic of sucrase in the yeast cell (62, 155). 



It has long been argued that the predominant sucrase of fungi is a 

 "glucosaccharase" differing from the "fructosaccharase" of yeast (121); 

 the history of this controversy is reviewed by Neuberg and Mandl 

 (156). The question has now been re-examined in the light of the 

 finding that both yeast and fungus sucrases are probably transfructosi- 

 dases. It appears that the two sucrases differ, but not in the way 

 formerly thought, and that it is not necessary to postulate a glucosac- 

 charase (15, 66). 



Transfructosidase activity has been demonstrated in several fungi, 



