Adenosine 5'-Triphosphate-Glucose and Phosphoenolpyruvate-Glucose Phosphotransferase Activities of Liver Microsomal Glucose 6-Phosphatase
| Autor: | Richard N. Horne, Robert C. Nordlie, T.L. Hanson, James D. Lueck |
|---|---|
| Rok vydání: | 1970 |
| Předmět: |
chemistry.chemical_classification
medicine.medical_specialty biology Cell Biology Phosphate Biochemistry Adenosine Cofactor Phosphotransferase chemistry.chemical_compound Hydrolysis Endocrinology Enzyme chemistry Internal medicine medicine Microsome biology.protein Molecular Biology Glucose 6-phosphatase medicine.drug |
| Zdroj: | Journal of Biological Chemistry. 245:6078-6084 |
| ISSN: | 0021-9258 |
| DOI: | 10.1016/s0021-9258(18)62666-3 |
| Popis: | Adenosine 5'-triphosphate-glucose and phosphoenolpyruvate-glucose phosphotransferase activities of rat liver microsomes have been studied. Evidence for the common identity of these activities with classical d-glucose 6-phosphate phosphohydrolase (EC 3.1.3.9) is presented. All activities were equally susceptible to mild heating. Both phosphate compounds inhibited the hydrolysis of glucose 6-phosphate competitively, and Ki values thus assessed agreed closely with Km values for these relatively abundant high energy phosphate compounds functioning as phosphoryl donors in their respective synthetic reactions. The pH optima for both phosphotransferase activities, approximately 4.5 in the absence of detergent, were significantly shifted towards neutrality by the cationic detergent cetyltrimethylammonium bromide (cetrimide) and by palmityl coenzyme A. Kinetic studies at pH 5.5 revealed that Km (and Ki) values for phosphate substrates (but not glucose) were quite markedly altered by variations in ionic strength or cetrimide concentrations. In contrast, Vmax values were little affected. Responses of levels of ATP-glucose phosphotransferase activity to experimental diabetes, insulin or cortisone therapy, adrenalectomy, and acute fasting were studied with fresh microsomal suspensions and with such preparations to which deoxycholate had been added. The patterns of response observed were in all instances fully comparable with those previously noted with inorganic pyrophosphate-glucose phosphotransferase activity. Relative levels of the subject activities were compared with other hydrolytic and synthetic activities of the enzyme. It is concluded that physiologically significant roles for these activities are feasible, but because of the comparatively low levels of activities with ATP and phosphopyruvate and their acid pH optima, such roles, if manifest, are likely to be highly specialized. |
| Databáze: | OpenAIRE |
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