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T Børresen

Publications and source records attributed to T Børresen.

14 recordsLinked to original sources
PubMed1992

Inhibition of microsomal glucose 6-phosphatase by unsaturated aliphatic aldehydes and ketones.

Aldehydes and ketones with one double bond conjugated to the carbonyl group inhibited the enzyme glucose 6-phosphatase, which is embedded in the microsomal membrane. The Michaelis constant, Km and the maximal rate of reaction, V, were affected in a way dependent on the inhibitor's chain-length: trans-2-pentenal and 1-penten-3-one increased Km linearly with concentration and had almost no effect on V, whereas trans-2-nonenal caused a large increase in V but only a small and non-linear change in Km. The effect of the short-chain aldehydes on the kinetic parameters increased with chain-length, but pentenone increased Km more than did trans-2-heptenal and conjugated dienals did not act as inhibitors. Therefore, sterical effects apparently are of importance. Washing the microsomes after incubation with hexenal or heptenal did not substantially decrease the inhibition, but with nonenal the inhibition was reduced by washing. Inhibition by the SH-group blocking reagent p-hydroxymercuribenzoate was competitive to inhibition by the alkenals. It is concluded that the alpha-beta unsaturated oxo-compounds inhibit glucose 6-phosphatase by binding covalently to an important mercapto group and that perturbation of the enzyme's membrane environment also plays a part in the inhibition.

Aldehydes↗
PubMed1989

Purification and characterisation of tyrosine decarboxylase and aromatic-L-amino-acid decarboxylase.

Microbial tyrosine decarboxylase (EC 4.1.1.25) and mammalian aromatic-L-amino-acid decarboxylase (EC 4.1.1.28) catalyse the formation of tyramine from L-tyrosine. These enzymes were characterised after isolation to purity by methods including fast polymer liquid chromatography (FPLC). Tyrosine decarboxylase was isolated from Streptococcus faecalis by FPLC anion exchange chromatography (11-times purification; 72% recovery; 23.2 U/mg protein). FPLC on Phenyl-Superose resulted in purification to 115 U/mg protein. Aromatic-L-amino-acid decarboxylase was isolated from pig kidney by ammonium sulfate fractionation, DEAE chromatography, and FPLC anion exchange chromatography (21-times purification; 22% recovery; 0.71 U/mg protein). By FPLC chromatofocusing, tyrosine decarboxylase eluted at pH 4.3 and aromatic-L-amino-acid decarboxylase at pH 5.0. Isoelectric focusing of tyrosine decarboxylase gave two bands (pI 4.4 and 4.5). With pyridoxal 5'-phosphate removed by ultrafiltration, only one band (pI 4.4) appeared, and SDS polyacrylamide electrophoresis confirmed the purity. FPLC gel filtration resulted in molecular weights 143,000 and 86,000, respectively, for tyrosine decarboxylase and aromatic-L-amino-acid decarboxylase. In SDS electrophoresis, tyrosine decarboxylase had the monomer molecular weight 75,000, showing a dimer structure for the enzyme.

Chromatography, Gel↗
PubMed1981

Influence of calcium infusion on urinary cyclic AMP and phosphate in hyperparathyroidism.

Urinary cyclic AMP (cAMP) and phosphate were measured before and after calcium infusion in 12 patients with operatively verified primary hyperparathyroidism (PHP) and in 12 healthy persons. In normal subjects infusion of calcium caused a reduction in urinary cAMP directly correlated to the preinfusion values and inversely correlated to the serum calcium concentration determined as albumin-corrected serum calcium. In normal subjects with high normal albumin-corrected serum calcium the infusion of calcium caused no or only a small depression in the urinary excretion of cAMP. Changes in phosphate excretion were not correlated to the calcium concentration. Four of the 12 hyperparathyroid patients showed normal relative suppression in urinary cAMP after the infusion of calcium, and 5 had normal suppression of phosphate excretion. It is concluded that some patients with PHP retain calcium-sensitive secretion of PTH, and that the classical calcium infusion test is of doubtful value in the diagnosis of PHP.

Adolescent↗
PubMed1981

Effect of furosemide on parathyroid hormone stimulated guinea pig renal adenylate cyclase and thyrotrophin and fluoride stimulated human thyroid adenylate cyclase.

The effect of furosemide 8 X 10(-4) mol/l an 8 X 10(-5) mol/l on parathyroid hormone stimulated adenylate cyclase was studied in renal tissue slices from guinea pigs. Furosemide caused a dose-dependent inhibition of the effect of parathyroid hormone on production of cyclic AMP, without having any significant effect on the basal cyclic AMP production. Furosemide in similar concentrations did not inhibit the stimulatory effect of thyrotrophin and fluoride in human thyroid homogenates suggesting that furosemide is not an universal inhibitor of adenylate cyclase and that the inhibition is not caused by a direct action of furosemide on the adenylate cyclase enzyme. Furosemide did not interfere with binding of cyclic AMP to cyclic AMP binding protein kinase from rabbit muscle. The results indicate that furosemide exerts an inhibitory influence either upon binding of parathyroid hormone to renal receptors or upon transmission of impulse from receptor to adenylate cyclase. The inhibitory influence of furosemide on parathyroid hormone action in kidney could explain the value of furosemide in the acute treatment of hypercalcaemia, but also suggest that chronic treatment with furosemide might interfere with normal calcium metabolism.

Adenylyl Cyclases↗
PubMed1981

Appendico-vesical fistula and persistent urachus in a patient with hematuria.

A 35-year-old man had been treated with sulfamethizole on 6 occasions because of recurrent urinary tract infections. Furthermore, he had experienced diffuse monosymptomatic hematuria for 15 years. Cystoscopy and biopsy demonstrated irregular intestinal mucosa. Physical examination and intravenous urography were normal. Preoperative diagnosis was urachus-derived adenoma with the possibility of adenocarcinoma. At operation a typical urachus and--surprisingly--an appendico-vesical fistula was found.

Adult↗
PubMed1980

Decreased norepinephrine concentration in normal tissue neighboring a malignant tumor.

We observed in five adenocarcinomas that norepinephrine as well as nerve fibers were absent from tumor tissue. The number of nerve fibers in normal tissue neighboring the tumor was normal. In contrast, norepinephrine concentration was decreased in normal tissue immediately surrounding tumor and increased in a stepwise fashion with the distance from tumor. Since there is evidence that some catecholamines possess antitumor activity, we suggest that depletion of catecholamines and perhaps other neurotransmitters in normal tissue neighboring a tumor may be of importance for invasion and accelerated malignant growth.

Adenocarcinoma↗