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Translocation of sugars into rat liver lysosomes. Evidence against a common carrier for D-glucose and D-ribose.

ABSTRACT: A conflict exists in the literature concerning the mode of translocation of D-glucose and D-ribose across the lysosome membrane. The more rapid net uptake of ribose, when measured by the osmotic-protection technique, has been attributed either to its smaller size and lower hydrogen-bonding capacity, or to a lower affinity for a transport system shared by both sugars. The latency of acid beta-hexosaminidase in isolated rat liver lysosomes was measured after preincubation for periods up to 1 h in various solutions containing glucose and/or ribose, and in some cases sucrose. After confirmation of the superior osmotic protection afforded by glucose (than by ribose), it was shown that a solution 0.125 M in both glucose and ribose provided protection intermediate between that given by 0.25 M-glucose and that given by 0.25 M-ribose. This result is inconsistent with the common-carrier hypothesis.

SUBMITTER: Bird SJ

PROVIDER: S-EPMC1148222 | biostudies-other | 1987 Aug

REPOSITORIES: biostudies-other

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Project description:The insulin effect on glucose uptake is not sufficiently explained by a simple glucose-carrier translocation model. Recent studies rather suggest a two-step model of carrier translocation and carrier activation. We used several pharmacological tools to characterize the proposed model further. We found that inositol phosphate (IP)-oligosaccharides isolated from the drug Actovegin, as well as the alkaloid vinblastine, show a partial insulin-like effect on glucose-transport activity of fat-cells (3-O-methylglucose uptake, expressed as % of equilibrium value per 4 s: basal 5.8%, insulin 59%, IP-oligosaccharides 30%, vinblastine 29%) without inducing carrier translocation. On the other hand, two newly developed anti-diabetic compounds (alpha-activated carbonic acids, BM 130795 and BM 13907) induced carrier translocation to the same extent as insulin and phorbol esters [cytochalasin-B-binding sites in plasma membranes: basal 5 pmol/mg of protein, insulin 13 pmol/mg of protein, TPA (12-O-tetradecanoylphorbol 13-acetate) 11.8 pmol/mg of protein, BM 130795 10.8 pmol/mg of protein], but produce also only 40-50% of the insulin effect on glucose-transport activity (basal 5.8%, insulin 59%, TPA 23%, BM 130795 35%). Almost the full insulin effect was mimicked by a combination of phorbol esters and IP-oligosaccharides (basal 7%, insulin 50%, IP-oligosaccharides 30%, TPA 23%, IP-oligosaccharides + TPA 45%). None of these substances stimulated insulin-receptor kinase in vitro or in vivo, suggesting a post-kinase site of action. The data confirm the following aspects of the proposed model: (1) carrier translocation and carrier activation are two independently regulated processes; (2) the full insulin effect is mimicked only by a simultaneous stimulation of carrier translocation and intrinsic carrier activity, suggesting that insulin acts through a synergism of both mechanisms; (3) IP-oligosaccharides might be involved in the transmission of a stimulatory signal on carrier activity.

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Translocation of sugars into rat liver lysosomes. Evidence against a common carrier for D-glucose and D-ribose.

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