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L Engström

Publications and source records attributed to L Engström.

At least 73 records · Page 4Linked to original sources
PubMed1978

Endogenous substrates of protein kinase in rat liver cell sap under different dietary conditions.

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.

Animals↗
PubMed1978

Proteolytic modification of pig and rat liver pyruvate kinase type L including phosphorylatable site.

The phosphorylated or phosphate-accepting site of pyruvate kinase from pig and rat liver was removed without inactivation by incubation with subtilisin. At different time intervals the subtilisin was inactivated with phenylmethylsulfonyl fluoride and the amount of remaining phosphorylatable or phosphorylated sites of pyruvate kinase estimated by incubation with an excess of [32P]-ATP and protein kinase. It was found that to get the same rate of modification the subtilisin concentration required to modify unphosphorylated pyruvate kinase was approximately ten times higher than that used for removal of the phosphorylated site of phosphorylated site of phosphorylated enzyme. It was shown that the proteolytically-modified pyruvate kinase had an increased apparent Km for phosphoenolpyruvate without a change in V, when compared to unmodified unphosphorylated and phosphorylated pyruvate kinase. The removal of the phosphorylated site was not associated with loss of the allosteric sites for ATP and Fru-1,6-P2. The possibility that phosphorylation of the pyruvate kinase increases its degradation rate in vivo is briefly discussed.

Adenosine Triphosphate↗
PubMed1977

Purification and characterization of pig kidney pyruvate kinase (type A).

Pyruvate kinase type A was purified from pig kidney with a yield of 9%. The final enzyme fraction had a specific activity of 500 units/mg of protein. The enzyme appeared to be homogeneous on polyacrylamide gel electrophoresis in detergent and in ultracentrifugation experiments. The molecular weight of the enzyme was found to be 210,000 with the use of ultracentrifugation and 249,000 at gel chromatography. The sedimentation coefficient (S degrees 20, w) was calculated to be 9.8 S. For the reduced and alkylated pyruvate kinase, a molecular weight of 60,000 was found with the use of several methods. The Stokes radius for the enzyme was calculated to be 56 A. No NH2-terminal amino acid was detected in the enzyme, and the only findings in carbohydrate analyses of the kidney pyruvate kinase were trace amounts of glucose. The isoelectric point of the enzyme was estimated to be pH 5.6. Pig kidney pyruvate kinase type A was not phosphorylated on incubation with ATP and cyclic 3':5'-AMP-dependent protein kinase. The amino acid compositions of pig kidney and pig muscle pyruvate kinases were very similar and differed clearly from that of pig liver pyruvate kinase.

Amino Acid Sequence↗
PubMed1977

Studies on the cyclic 3':5'-AMP-stimulated pig liver protein kinase reaction with pyruvate kinase as substrate.

The phosphorylation of pig liver pyruvate kinase by cyclic adenosine 3':5'-monophosphate-dependent protein kinase has been studied. For comparison, mixed histone and a synthetic heptapeptide were also used as substrates. Protein kinase was purified by chromatography on DEAE-cellulose, hydroxyapatite, and Sephadex G-200. The enzyme was stimulated by cyclic AMP with apparent Ka values of 2.5 and 0.8 x 10-7 M for pyruvate kinase and histone substrates, respectively. Divalent cations were essential for the activity of the protein kinase. Variation of the concentration of ATP resulted in approximately straight lines in Lineweaver-Burk plots for the phosphorylation of both pyruvate kinase and mixed histone. The apparent Km values for ATP were 21 and 11 muM, respectively. The phosphorylation rate increased with the concentration of pyruvate kinase even at a concentration of 2 muM pyruvate kinase. At a high ionic strength, the phosphorylation rate of both pyruvate kinase and histone decreased. The phosphorylation rate varied markedly with pH in imidazole/HC1 and Tris/HC1 buffers. At slightly alkaline pH values, pyruvate kinase was phosphorylated at a much higher rate than pH7, but this was not the case for histone. At pH 8.5, the phosphorylation rate of pyruvate kinase was 3.5 times the rate at pH 7, while the corresponding increase for the histone phosphorylation was 50 per cent. In potassium phosphate buffers, the phosphorylation rate of both substrates did not change significantly over the pH range studied. Arrhenius' plots of the protein kinase reaction resulted in a break at about 10 degrees when pyruvate kinase was used as substrate, whereas a straight line was obtained when using histone. The negative allosteric effectors of pyruvate kinase, alanine, and phenylalanine, increased the phosphorylation rate of pyruvate kinase at pH 8 by 50 and 120 per cent, respectively. The same effectors did not influence the phosphorylation rate of mixed histone or a synthetic heptapeptide. It is concluded that the conformations adopted by pyruvate kinase in the presence of allosteric inhibitors make it a better substrate for the protein kinase.

Adenosine Triphosphate↗
PubMed1976

Studies on the kinetic effects of adenosine-3':5'-monophosphate-dependent phosphorylation of purified pig-liver pyruvate kinase type L.

The effect of cyclic-AMP-dependent phosphorylation on the activity of isolated pig liver pyruvate kinase was studied. It was found that the major kinetic effect of the phosphorylation was to reduce the affinity for the substrate phosphoenolpyruvate, K0.5 for this substrate increasing from 0.3 to 0.9 mM upon phosphorylation. The cooperative effect with phosphoenolpyruvate was enhanced, the Hill constant nH increasing concomitantly from 1.1 to 1.5. V was unaltered. The change in activity occurred in parallel with the phosphate incorporation, except during the initial part of the reaction, when inactivation was correspondingly slower. The affinity for the second substrate ADP was unchanged, with an apparent Km of 0.3 mM at saturating concentration of phosphoenolpyruvate. Likewise, the requirement for potassium was unaffected, whereas the phosphoenzyme required a higher concentration of magnesium ions for maximal activity, compared with the control enzyme. The inhibitory effect of the phosphorylation was counteracted by positive effectors, fructose 1,6-biphosphate in micromolar concentrations completely activated the phosphoenzyme, resulting in an enzyme with properties similar to the fructose 1,6-biphosphate-activated unphosphorylated enzyme, with K0.5 for phosphoenolpyruvate about 0.025 mM and with a Hill constant of 1.1. Hydrogen ions were also effective in activating the phosphoenzyme. Thus, when pH was lowered from 8 to 6.5 the inhibition due to phosphorylation was abolished. The phosphoenzyme was sensitive to further inhibition by negative effectors such as ATP and alanine. 2 mM ATP increased K0.5 for phosphoenolpyruvate to 1.5 mM and nH to 2.3. The corresponding values with alanine were 1.3 mM and 1.9. Phosphorylation is thought to be an additional mechanism of inhibition of the enzyme under gluconeogenetic conditions.

Adenosine Diphosphate↗
PubMed1976

Comparative kinetic studies on the L-type pyruvate kinase from rat liver and the enzyme phosphorylated by cyclic 3', 5'-AMP-stimulated protein kinase.

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.

Adenosine Diphosphate↗
PubMed1975

Acid-base and electrolyte balance in infants of diabetic mothers. Vaginal delivery versus caesarean section.

The acid-base and electrolyte balance of 30 women studied at delivery and in their infants during the first 48 h. 18 women were diabetics, 10 of these were delivered vaginally (DMvag) and 8 by elective caesarean section (DMcs). 12 healthy women were vaginally delivered (HMvag). The infants of diabetic mothers (IDM) received active infusion therapy. At birth the DMvag and their infants (IDMvag) had a more pronounced metabolic acidosis than the DMcs and their babies (IDMcs). The largest metabolic acidosis occurred, however, in the group of HMvag and their infants (IHMvag). After birth no significant differences were obtained in the acid-base and electrolyte balance between IDMvag and IDMcs. The plasma potassium level remained lower in IDM than in IHM. The study stress the importance of adequate management of diabetes in pregnancy in combination with active intravenous therapy during delivery and to the infant in the immediate neonatal period. The slightly larger metabolic acidosis seen in combination with vaginal delivery suggests that this mode of delivery should not be attempted uncritically in diabetic women.

Acid-Base Equilibrium↗