Presence of Ketohexokinase EC 2.7.1.3 in Bovine Lenses

Ohrloff, C.; Hockwin, O.

doi:10.1159/000266027

Cited by 14 publications

(5 citation statements)

References 3 publications

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“…Earlier investigations on bovine lenses showed that fructose can be directly phosphorylated to fructose-l-phosphate [Ohrloff and Hockwin, 1973]. This reaction is catalyzed by the enzyme ketohexokinase, an enzyme which could in the meantime also be determined in normal and opacified human lenses [Ohrloff and Hockwin, in press].…”

Section: Resultsmentioning

confidence: 99%

Investigations of the Enzymes Involved in the Fructose Breakdown in the Cattle Lens

1982

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By introducing fructose into the glycolysis, it is possible to stimulate ATP formation. As is the case in animal experiments, in human lenses, too, the first step is the phosphorylation to fructose-1-phosphate via the enzyme ketohexokinase. The present investigation deals with the question whether enzymes present in the lens are responsible for the further steps in fructose degradation. Particularly the aldolase isoenzyme C splits fructose-1-phosphate into glyceraldehyde and dihydroxyacetone phosphate in the same way as in glucose catabolism. Dihydroxyacetone phosphate can further be directly degraded and thus utilized to ATP formation. From glyceraldehyde, glycerol (aldose reductase) or glycerate (aldehyde dehydrogenase) can be formed. The presence of triosekinase, which phosphorylates glyceraldehyde directly to glyceraldehyde-3-phosphate, could only be determined in the lens tissue of young animals. The presence of glycerokinase (glycerol → glycerophosphate) could not be verified. Thus, in the old lens tissue 1 ATP molecule net per fructose molecule can be formed. In older age, the glucose breakdown is limited by hexokinase and phosphofructokinase, so that the glucose, after transformation via the sorbitol pathway to fructose, can also be utilized for the energy metabolism.

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Section: Resultsmentioning

confidence: 99%

Investigations of the Enzymes Involved in the Fructose Breakdown in the Cattle Lens

1982

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“…Not only the determination of the enzy mes necessary for fructose breakdown [ Ohrloff and Hockwin, 1973;O hrlofftt al. 1974, 1982 but almost all the incubation experi- The results are expressed in pmol/g tissue/180 min.…”

Section: Discussionmentioning

confidence: 99%

Fructose, Fructose 1-Phosphate, and Glyceraldehyde Breakdown in Carbohydrate Metabolism

Ohrloff¹,

Zierz²,

Hockwin³

1983

Ophthalmic Res

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Recent investigations showed that all enzymes that are involved in the catabolism of fructose via fructose 1-phosphate (F-1-p) are present in the bovine lens. The present studies were performed to provide information regarding the extent to which fructose, F-1-p and glyceraldehyde (GA) are actually catabolized via this pathway, and how they increase the lactate, α-glycerophosphate and glycerol concentrations. Incubation was performed with a homogenate of bovine lens equator. F-1-p, and particularly fructose + ATP, considerably increased lactate and α-glycerophosphate concentrations, while the glycerol concentration remained unchanged compared to controls. Lactate formation through GA was not observed; while small amounts of glycerol and α- glycerophosphate are formed, it seems that the major part is transformed to glycerate. The results show that the further breakdown of lenticular fructose occurs via F-1-p and that the phosphorylated C3 fragments (dihydroxy-acetone phosphate) are transferred to the energy metabolism, which is not the case with GA.

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“…According Enzyme heterogeneity in bovine lenses during aging 183 to the protein profile obtained, enzyme measurements were performed in selected frac tions. Measurements of enzyme activities were performed for aldose reductase (AR) according to Haymann and Kinoshiia [1965], for sorbitol dehydrogenase (SDH) accord ing to Beromeyer [1974], and for ketohexokinase (KHK) according to Ohrloff and Hockwin [1973], Aliquots of separated fractions were used as follows: SD H : 0.1 ml; AR: 0.5 ml; K H K : 0.5 ml. Photometer: Zeiss PMQ II, 340nm,d = I cm, at room temperature.…”

Section: Separation O F Water-soluble Proteinsmentioning

confidence: 99%

Enzyme Heterogeneity of Aldolase Reductase (EC 1.1.1.2), Sorbitol Dehydrogenase (EC 1.1.1.14) and Ketohexokinase (EC 2.7.1.3.) in Bovine Lenses

et al. 1977

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Separation of water-soluble protein of bovine lenses by Sepharose 6-B and subsequent measurement of the enzyme activities of aldose reductase, sorbitol dehydrogenase, and ketohexokinase show an enzyme heterogeneity for all three enzymes of the sorbitol pathway. While for SDH four modifications could be detected, AR and KHK showed at least two modifications. As concerns SDH and KHK, the arrangement within the elution profile and distribution of the activity among the individual modifications vary with age. Considering the results of Bous et al. for PFK and of Banroques et al. for aldolase, our findings on enzyme modifications may be considered as so-called metazymes originating from postsynthetic changes of the enzyme protein.

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Presence of Ketohexokinase EC 2.7.1.3 in Bovine Lenses

Abstract: Ketohexokinase (EC 2.7.1.3) is present in bovine lenses and facilitates fructose degradation to fructose-1-phosphate. The importance of this finding to lens carbohydrate metabolism is discussed.

Cited by 14 publications

References 3 publications

Investigations of the Enzymes Involved in the Fructose Breakdown in the Cattle Lens

Investigations of the Enzymes Involved in the Fructose Breakdown in the Cattle Lens

Fructose, Fructose 1-Phosphate, and Glyceraldehyde Breakdown in Carbohydrate Metabolism

Enzyme Heterogeneity of Aldolase Reductase (EC 1.1.1.2), Sorbitol Dehydrogenase (EC 1.1.1.14) and Ketohexokinase (EC 2.7.1.3.) in Bovine Lenses

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