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| 2. |
- Dahlqvist, Ulla, et al.
(författare)
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Endogenous substrates of protein kinase in rat liver cell sap under different dietary conditions
- 1978
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 1878-2434 .- 0304-4165. ; 540:1, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- Liver cell sap from normally fed rats, rats fed with a high-carbohydrate diet and fasted rats was chromatographed on DEAE-cellulose (pH 7.0). The chromatogram from each diet group was analyzed for pyruvate kinase activity and endogenous substrates of cyclic AMP-stimulated protein kinase. The materials were pooled into five phosphorylatable fractions, in each of which phosphate incorporation at 0.1 mM and 1.0 mM [32P]ATP in the presence of cyclic AMP and protein kinase was determined. For characterization of the phosphorylatable components, thin-layer gel chromatography on Sephadex G-200 and polyacrylamide gel electrophoresis in detergent were used for determination of native and minimal molecular weights, respectively. Except for pyruvate kinase, eight components which incorporated at least 0.05 nmol of [32P]phosphate/g of liver were detected. The phosphorylation of four of them was stimulated by cyclic AMP. Their minimal molecular weights were 42000, 21000, 52000 and 49000. The component with a minimal molecular weight of 42000 seemed to have a native molecular weight of 160000. Both the 21000 and the 52000 component had a native molecular weight of about 110000-120000. The protein with a minimal molecular weight of 49000 could not be correlated with certainty to a native molecular weight. The proteins whose phosphorylation was not stimulated by cyclic AMP had minimal molecular weights of 54000, 39000, 34000 and 22000.
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| 3. |
- Edlund, Bror, et al.
(författare)
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Amino acid sequence at the phosphorylated site of rat liver pyruvate kinase
- 1975
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - 0006-291X .- 1090-2104. ; 67:4, s. 1516-1521
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Tidskriftsartikel (refereegranskat)abstract
- One dominating peptic phosphopeptide, Asx-Thr-Lys-Gly-Pro-Glx-Ile-Glx-Thr-Gly-Val-Leu-Arg-Arg-Ala-(32P)SerP-Val-Ala-Glx-Leu, was obtained from rat liver pyruvate kinase (type L) phosphorylated by cyclic 3′,5′-AMP-stimulated protein kinase from the same tissue. The sequence around the phosphorylated serine residue is similar to that of a corresponding but smaller peptic phosphopeptide previously isolated from pig liver (type L) pyruvate kinase, Leu-Arg-Arg-Ala-(32P)SerP-Leu.
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| 4. |
- Ek, Pia, et al.
(författare)
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Comparative kinetic studies on the L-type pyruvate kinase from rat liver and the enzyme phosphorylated by cyclic 3´, 5´-AMP-stimulated protein kinase
- 1976
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Ingår i: Biochimica et Biophysica Acta. - 0006-3002 .- 1878-2434. ; 429:2, s. 374-382
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of rat liver L-type pyruvate kinase (EC 2.7.1.40), phosphorylated with cyclic AMP-stimulated protein kinase from the same source, and the unphosphorylated enzyme have been compared. The effects of pH and various concentrations of substrates, Mg2+, K+ and modifiers were studied. In the absence of fructose 1, 6-diphosphate at pH 7.3, the phosphorylated pyruvate kinase appeared to have a lower affinity for phosphoenolpyruvate (K0.5=0.8 mM) than the unphosphorylated enzyme (K0.5=0.3 mM). The enzyme activity vs. phosphoenolpyruvate concentration curve was more sigmoidal for the phosphorylated enzyme with a Hill coefficient of 2.6 compared to 1.6 for the unphosphorylated enzyme. Fructose 1, 6-diphosphate increased the apparent affinity of both enzyme forms for phosphoenolpyruvate. At saturating concentrations of this activator, the kinetics of both enzyme forms were transformed to approximately the same hyperbolic curve, with a Hill coefficient of 1.0 and K0.5 of about 0.04 mM for phosphoenolpyruvate. The apparent affinity of the enzyme for fructose 1, 6-diphosphate was high at 0.2 mM phosphoenolpyruvate with a K0.5=0.06 muM for the unphosphorylated pyruvate kinase and 0.13 muM for the phosphorylated enzyme. However, in the presence of 0.5 mM alanine plus 1.5 mM ATP, a higher fructose 1, 6-diphosphate concentration was needed for activation, with K0.5 of 0.4 muM for the unphosphorylated enzyme and of 1.4 muM for the phosphorylated enzyme. The results obtained strongly indicate that phosphorylation of pyruvate kinase may also inhibit the enzyme in vivo. Such an inhibition should be important during gluconeogenesis.
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| 5. |
- Humble, Elisabet, et al.
(författare)
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Amino acid sequence at the phosphorylated site of rat liver fructose-1,6-diphosphatase and phosphorylation of a corresponding synthetic peptide
- 1979
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - 0006-291X .- 1090-2104. ; 90:3, s. 1064-1072
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Tidskriftsartikel (refereegranskat)abstract
- Rat liver fructose-1,6-diphosphatase was phosphorylated with (32P)ATP and the catalytic subunit of cyclic AMP-dependent protein kinase from pig muscle. After digestion with pepsin, α-chymotrypsin and subtilisin a peptide with the amino-terminal sequence Ser-Arg-Tyr-(32P)SerP-Leu-Pro-Leu-Pro was isolated. A synthetic unphosphorylated heptapeptide with the same amino acid sequence, ending with leucine, was phosphorylated with an apparent Km of 400 μM, while the apparent Km value for fructose-1,6-diphosphatase was 30 μM (subunit concentration). The Vmax value was 20 times higher for the peptide than for the enzyme.
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