The discovery of β-galactosidase (original) (raw)

1989, Trends in Biochemical Sciences

keeps the memory of Beijerinck, its first professor, alive by maintaining a 'Beijerinck-room' in the attic of the building. In addition to manuscripts and laboratory notebooks, this room contains some of his chemicals and biological preparations, and it was here that we recently found a 90-year old lactase preparation. Even after storage under suboptimal conditions, the preparation still exhibited measurable enzyme activities. Lactase ~-Galactosidase (lactase; EC 3.2.1.23) is a well known and extensively studied enzyme which catalyses the hydrolysis of milk sugar (lactose) into the monosaccharides D-galactose and D-glucose. Lactase is produced by a wide variety of organisms including bacteria, yeasts and fungi. Lactases of yeasts and filamentous fungi are of industrial importance in the saccharification of whey permeate, allowing the subsequent alcoholic fermentation with Saccharomyces cerevisiae. The enzyme is also applied in the treatment of skimmed milk to allow its consumption in developing countries where the incidence of lactose intolerance is high. The lactose operon in Escherichia coli, first described in 1961 by Jacob and Monod, has had an enormous impact on modern molecular genetics. At present, the lacZ gene and lacI-Z fusions are widely used as indicators.of gene integration and promoter activity. Lactase, encoded by the lacZ gene, can easily be detected by using the artificial substrate o-nitrophenyl-[~-Dgalactopyranoside (ONPG). Lactase was among the first hydrolases to be discovered. In the 1880s and 1890s, many enzymes were described. In most cases yeasts (the word enzyme literally means 'in yeast') were used as a source of these proteins (e.g. invertase, maltase and trehalase). The first report that yeast cells may split lactose enzy

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