228 IMMUNO-CATALYSIS 



The enzyme is quite specific with respect to substrates, and causes no 

 detectable phosphorolysis of starch, mahose, lactose, trehalose, or 

 raffinose. Fructose cannot be replaced by fructose-6-phosphate, fruc- 

 tose- 1,6-diphosphate, etc. However, two ketoses, 1-sorbose and 

 d-ketoxylose have been shown to react with glucose- 1 -phosphate under 

 the influence of the phosphorylase to form two new analogues (a-D- 

 glucosido-a-L-sorboside and a-o-glucosido-^S-D-ketoxyloside) of sucrose, 

 unknown in nature (DoudorofF, et ah, 1944). Neither of these two 

 analogues of sucrose was found to be susceptible to hydrolysis with 

 yeast invertase. 



Serologically Active Dextran and Levulan. The synthesis of poly- 

 saccharides not involving the participation of phosphorolytic reactions 

 is that of the synthesis of dextran or levulan from sucrose. Dextran, 

 which is a polymer of glucose in which the hexose units are joined 

 through 1,6-linkages, is produced in large quantities by L. mesenter- 

 oides when the latter is grown with sucrose, but not with invert sugar 

 (Beijerinek, 1912; Hassid et ah, 1940). Levulan, a fructose polymer 

 having the 2,6-linkage has been known to be synthesized by many 

 species of bacteria. 



Cell-free enzyme preparations made from L. mesenteroides (Hehre, 

 1942; Hehre, et ah 1943; Hestrin and Avinieri-Shapiro, 1944) have 

 been shown to catalyze the synthesis of both dextran and levulan with- 

 out requiring the participation of organic or inorganic phosphate. 



nCjoHooOn > nCeHioOe + (CeHioOs)™ 



Sucrose fructose dextran 



MC12H22O11 > WC6H12O6 + (CeHioOg)^ 



Sucrose glucose levulan 



The mechanism of the synthesis of dextran or levulan from sucrose 

 appears to be the exchange of an already existing glycosidic linkage for 

 a new glycosidic linkage. Failure of the enzyme to catalyze the 

 synthesis of dextran from glucose, or fructose, or a mixture of glucose 

 and fructose, or from glucose- 1 -phosphate, frutose-6-phosphate, and 

 failure of yeast inulase added to levan-sucrase to induce levulan pro- 

 duction from inulin indicates (Leibowitz and Hestrin, 1945) that the 

 polymerization of dextran or levulan from sucrose proceeds only on 

 the sucrose grouping, without necessitating primary hydrolytic cleavage 

 of the disaccharide. 



