Guanosine Nucleosidase from Germinated Barley. N. Prentice, U.S. Department of Agriculture, Agricultural Research Service, Cereal Crops Research Unit, 501 N. Walnut St., Madison, WI 53705. J. Am. Soc. Brew. Chem. 46:0092, 1988.

Guanosine nucleosidase was extracted from germinated Morex barley and highly purified. The molecular weight was found to be 29 to 33 kDa. The activation energy was 12.1 kcal per mole, the pI and optimum pH were 5.3 and 5.5, respectively, the pH stability range 6.5 to 7.5, and the optimum temperature 40° C. Guanosine concentration was found to increase during mashing from 3 to 83 mg/L, but the guanine level remained unchanged at about 19 mg/L. This suggests that nucleic acid breakdown via guanidine nucleotidase occurs during mashing, but because mash pH and temperatures are not compatible with the malt guanosine nucleosidase, the final conversion from guanosine to guanine cannot occur.

Keywords: Brewers' mash, Enzyme parameters, Guanine, Guanosine, Guanosinase