Shlomo Hestrin

Carbohydrases in Saccharomyces haploid stocks of defined genotype. II. Gene-controlled induction of glucosidases by α-glucosides☆☆☆

Abstract 1. 1. Yeast containing the gene MA formed both maltase and glucosucrase when grown on maltose and lost these responses to maltose when MA was replaced by its recessive allele. 2. 2. Yeast containing the gene MG formed both α-methyl glucosidase and glucosucrase when grown on α-methyl glucoside and lost these responses to α-methyl glucoside when MG was replaced by the recessive allele. 3. 3. Yeast containing both MA and MG responded heterologously to growth on maltose with the appearance of the ability to ferment α-methyl glucoside as well as maltose, whereas yeast containing MA and lacking MG failed to ferment α-methyl glucoside after growth on maltose. 4. 4. Glucose inhibited the responses of the yeasts to maltose and α-methyl glucoside. 5. 5. α-Methyl glucoside inhibited the formation of maltase in response to maltose. 6. 6. The mode of the control of homologous and heterologous response to glucosides by genes MA and MG is discussed. 7. 7. It is noted that the inhibition of homologous response to glucosides by glucose provides the cells with a homeostatic mechanism for the regulation of their adaptive response.

An enzymic synthesis of a sucrose analog: α-d-xylopyranosyl-β-d-fructofuranoside☆

Abstract Levansucrase transferred the β-fructofuranosyl group of raffinose to the anomeric carbon of xylose. The disaccharide “xylsucrose” formed by this reaction has been isolated and is shown to be α- d -xylopyranosyl-β- d -fructofuranoside. Xylsucrose was hydrolyzed by ordinary yeast invertase and was utilized both as donor and acceptor by levansucrase. Some other sucrases (dextransucrase, amylosucrase, and a special yeast sucrase) were inert towards this sucrose analog. The substrate specificity of levansucrase and the possible role of sucrose analogs in biological polymer synthesis are discussed.