Enzymic hydrolysis of the carbon-fluorine bond of α-d-glucosyl fluoride by rat intestinal mucosa. Localization of intestinal maltase

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Abstract
Alpha-D-glucosyl fluoride was hydrolysed by an extract of rat intestinal mucosa. The pH optimum was 6.6 and the Km 0.4m[image] at 20[degree]. Activity was assayed by release of either glucose or fluoride. The [alpha]-D-glucosyl fluoride-hydrolase activity of the extract was associated with both mutarotase and [alpha]-D-glucosidase activities. Tris (5m[image]) inhibited both the [alpha]-D-glucosidase and [alpha]-D-glucosyl fluoride-hydrolase activities by 55% but did not inhibit mutarotase. The Ki of tris for both enxyme activities was 2m[image]. The extract did not hydrolyse melibiose and lactose. Mutarotase used both [alpha]-D-glucose and [beta]-L-arabinose as substrates but the glucosyl fluoride-hydrolase activity did not extend to [beta]-L-arabinosyl fluoride. The thermal stability of [alpha]-D-glucosidase and [alpha]-D-glucosyl fluoride-hydrolase was identical. Mutarotase was more thermolabile. A preparation of the brush border of intestinal epithelial cells contained both [alpha]-D-glucosyl fluoride-hydrolase and [alpha]-D-glucosidase activities. In each precipitate and washing the ratio of the two activities was the same. All the mutarotase activity was in the first supernatant. Agidex, a fungal amyloglucosi-dase, cleaved glucosyl fluoride in addition to maltose. Tris inhibited both activities and in each case the Ki was 3m[image]. The probable identity of [alpha]-D-glucosyl fluoride hydrolase with -D-glucosidase is discussed and a possible mechanism for the reaction suggested. Incubation of intestinal slices with [alpha]-D-glucosyl fluoride led to complete hydrolysis in 30 min. The glucose rapidly entered the cell and was metabolized, leaving the fluoride in the incubation medium. This constitutes a further proof that the intestinal [alpha]-D-glucosidase, although on the brush border, is located outside the site of active transport of sugars.