Glucose metabolism in the mucosa of the small intestine. A study of hexokinase activity

Abstract

1. The intracellular distribution of hexokinase activity was studied in the mucosa of rat and guinea-pig small intestine. In the rat 60% and in the guinea pig 45% of the hexokinase activity of homogenates were recovered in a total particulate fraction that contained only 5-17% of the homogenate activity of hexose phosphate isomerase, pyruvate kinase, lactate dehydrogenase and overall glycolysis (formation of lactate from glucose). 2. Fractionation of homogenates from guineapig small intestine showed that the particulate hexokinase activity was chiefly in the mitochondrial fraction with a small proportion in the nuclei plus brush-border fraction. 3. After chromatography of the particle-free supernatants on DEAE-cellulose, hexokinase types I and II were determined quantitatively. No evidence was obtained for the presence of hexokinase type III or glucokinase. In the preparations from guinea pigs, hexokinase types I and II amounted to 69% and 31% respectively of the eluted activity; the corresponding values for preparations from rats were 5.8% and 94.2%. 4. Total and specific hexokinase activities decreased significantly in homogenates and particle-free supernatants prepared from the intestinal mucosa of rats starved for 36hr. and increased again after re-feeding. The decrease in hexokinase activity in the particle-free supernatant from starved rats was chiefly due to a decrease in the type II enzyme.

Biochemical Consequences of the Anaphylactic Reaction

“…In order to establish the reproducibility of the system, we studied glucose oxidation by adjacent segments, and found that the amount of glucose oxidized per unit weight of segment differed somewhat in some cases and there was no regularity of change which could be related to the position of the segment in the ileum with respect to the ileocecal end. This finding is consistent with the variations of histological composition in the intestine (17), with the report of Binaghi and O sler (18) concerning the variability of the reaction of the intestine to histamine, serotonin and K+, and the variable dehydrogenase content along the guinea pig ileum re ported by Srivastava and H übscher (19). It was therefore decided to use the two strips of a segment of ileum as test and control tissues.…”

Influence of feeding fructose on fructose and glucose absorption in rat jejunum and ileum

“…In experiments using everted sacs of rat intestine and an incubation time of 45 min a significant conversion of D-fructose to glucose was observed [4]. Conversion of fructose to lactate may also occur [9,15]. Glycolytic activity in the supernatants of homogenate of intestinal mucosa of rats were comparable for Dglucose and D-fructose [15].…”

“…Other actively transported sugars like D-glucose and 3-O-Methylglucose were reported to cause no [15] or only moderate [8] inhibition of the absorption of D-fructose, while L-sorbose, a closely related isomer, had a somewhat more marked inhibitory effect [8,13]. From the latter findings it was concluded that the carrier-mediated mechanism is relatively specific for Dfructose, The results of the present experiments demonstrate that, in the rat at least, Dfructose uptake is distinctly influenced by the type of dietary sugar.…”

EFFECTS OF FASTING AND GLUCAGON ON THE KINETICS OF ACTIVE HEXOSE ABSORPTION ACROSS THE RAT DISTAL ILEUM IN VIVO

“…Furthermore, they were unlikely to be due to alterations in the metabolism of the transported sugar by the enterocyte since galactose is a hexose known to be poorly metabolized by the intestinal mucosa. The glycolytic activity of distal intestine is, in any case, much lower than that of the proximal region (Srivastava & Hubscher, 1966), absorption from the distal area being more dependent on metabolism of non-carbohydrate substrates (Barry, Matthews & Smyth, 1961).…”