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B A Skålhegg

Publications and source records attributed to B A Skålhegg.

10 recordsLinked to original sources
PubMed1977

Enzymatic Determination of bile acids. the NADP-specific 7alpha-hydroxysteroid dehydrogenase from P. testosteroni (ATCC 11996).

By use of the specific substrates, 7alpha-hydroxy-5beta-cholanic acid and 3alpha, 7alpha, 12alpha-trihydroxy-3,12-diacetyl-5beta-cholanic acid methyl ester, crude extracts of P. testosteroni grown on a steroid-containing medium have been shown to exhibit 7alpha-hydroxysteroid: NADP-oxidoreductase activity. The enzyme is highly specific for NADP. Both free and conjugated 7alpha-hydroxy bile acids can act as substrates, but those of low polarity (few hydroxyl groups) seem to be preferred, judging from initial reaction velocity studies. Optimal conditions appears to be at pH 8.5-9.5 and at 25 degress C. Free SH-groups are essential for maximum catalytic activity, since the enzyme is inhibited by SH-reacting substances such as p-chloromercuribenzoate and monoiodoacetic acid. Also the ketone-trapping agents hydrazine hydrate and semicarbazide act as inhibitors. Upon dilution, the storage stability is severely reduced, but this effect may be counteracted by the addition of glycerol at concentration of 20% or more. By gel filtration experiments on Sephadex G-100, the molecular weight was estimated to about 80,000.

Bile Acids and Salts↗
PubMed1977

Quantitative determination of serum bile acids using a 7alpha-hydroxysteroid dehydrogenase.

A crude 7alpha-hydroxysteroid dehydrogenase isolate from P. testosteroni requires NADP specifically and provides a simple and specific means for the determination of 7alpha-hydroxy bile acids and their conjugates. A specific and reliable enzymatic-fluorimetric method for the quantitative measurement of the primary bile acids in serum is described. Overall recovery from normal and jaundiced serum averaged 85%. The mean concentration of serum 7alpha-hydroxy bile acids in fasting, healthy subjects was 2.5 mumoles/1 (S.D. 1.45 AND RANGE 1.2-6.3), averaging 73% (S.D. 11.5) of the total, measured as the 3alpha-hydroxy bile acid concentration. In parenchymatous liver disease and cholestatic hepatobiliary disorders, the proportion of 7alpha-hydroxy bile acids was significantly increased, mean 92.5% (S.D. 6.6)(p less than 0.001).

Adult↗
PubMed1975

3Alpha-hydroxysteroid dehydrogenase from Pseudomonas testosteroni: kinetic properties with NAD and its thionicotinamide analogue.

The kinetics of 3alpha-hydroxysteroid : NAD oxidoreductase (EC 1.1.1.50) from Pseudomonas testosteroni (ATCC 11996) have been investigated. The kinetic analysis based on initial activity measurements and product inhibition studies, indicates that the addition of substrate to the enzyme and the release of products from it, follows an obligatory order (ordered bi bi mechanism). The ability of the enzyme to utilize the thionicotinamide analogue of NAD (sNAD) as cofactor has been investigated using various 3alpha-hydroxysteroids from both the C19, C21, and C24 series. The results show that the reaction velocity with sNAD as the cofactor is generally lower than with NAD. The decrease, however, varies considerably, being negligible with some steroids such as litocholic acid and deoxycholic acid and very pronounced with other such as tetrahydrocortisol and tetrahydrocortisone. The introduction of an 11beta-hydroxy or an 11-oxo group into the steroid molecule significantly reduces the ability of the enzyme to attack the 3alpha-hydroxy group. No such effect could be seen when the 11-hydroxy group was in the alpha-position. The results also indicate that, whereas NAD can serve as cofactor for both the monomeric and the dimeric forms of the enzyme, sNAD only acts as cofactor for the monomeric form. Thus sNAD is a valuable tool for the study of the reversible, concentration-depenedent monomeric-dimeric transition of the 3alpha-hydroxysteroid dehydrogenase.

Androstanes↗
PubMed1975

On the 3alpha-hydroxysteroid dehydrogenase from Pseudomonas testosteroni. The effect of denaturing agents.

Highly purified preparations of the 3alpha-hydroxysteroid:NAD- oxidoreductase (E.C.1.1.1.50) from Pseudomonas testosteroni (ATCC 11996) which consist of two major isoenzymes, with traces of a third, have been split into two enzymatically inactive polypeptides A and B by the use of sodium dodecylsulphate, urea and guanidinium hydrochloride. Both polypeptides have a molecular weight of 25,000 +/- 2,500 as shown by thin-layer gel chromatography and ultracentrifugations. They differ, however, in charge as shown by electrophoresis on cellulose acetate strips in the presence of 8 M urea. Each of the isoenzymes, have molecular weight of about 50,000 and thus consist of two subunits. The presence of the three isoenzymes may be explained by the following combinations of the subunits, AA, AB and BB. Close to 100% of the original activity towards the three substrates, androsterone tetrahydrocortisone and desoxycholate could be restored within 24 h when the inactivated enzyme was diluted in order to remove the effect of the denaturant.

Androsterone↗