Studies on sulphatases. I. The choice of substrate for the assay of rat-liver arylsulphatase

Estrone sulfatase: probing structural requirements for substrate and inhibitor recognition

The enzyme-catalyzed desulfation of steroids is a transformation that plays an important role in steroid biosynthesis. Conversion of steroid sulfates to unconjugated steroids may provide a source of steroids for processes such as steroid transport and the growth and proliferation of breast cancer. Steroid sulfatase catalyzes the hydrolysis of 3beta-hydroxysteroid sulfates. To identify structural features important in enzyme-inhibitor interaction, a variety of steroidal and non-steroidal phosphate esters were synthesized and tested as inhibitors of steroid sulfatase activity. We report that the basic structure for enzyme-inhibitor binding does not include the steroid nucleus. Furthermore, the hydrophobicity of the non-steroidal phosphates was determined to be an important factor for optimal inhibition. The monoanionic form of the phosphorylated compounds was found to be the inhibitory species. The best non-steroidal inhibitor of steroid sulfatase activity was n-lauroyl tryamine phosphate with a Ki of 3.6 microM and 520 nM at pH 7.5 and 7.0. The poorest non-steroidal based inhibitor of sulfatase activity was tetrahydronaphthyl phosphate with a Ki of 870 and 360 microM at pH 7.5 and 7.0.

Urinary t,t-muconic acid as an indicator of exposure to benzene

A method for rapidly determining t,t-muconic acid (MA) by high performance liquid chromatography was developed and successfully applied to urine samples from 152 workers exposed to benzene (64 men, 88 women) and 213 non-exposed controls (113 men, 100 women). The MA concentrations in urine correlated linearly with time weighted average benzene concentrations in the breath zone air of workers. A cross sectional balance study showed that about 2% of benzene inhaled is excreted into the urine as MA. The MA concentrations in the urine of the non-exposed was below the detection limit (less than 0.1 mg/l) in most cases, and the 95% lower confidence limit of MA for those exposed to benzene at 5 ppm (5.0 mg/l as a non-corrected value) was higher than the 97.5%-tile values for the non-exposed (1.4 mg/l). In practice, it was possible to separate those exposed to 6-7 ppm benzene from the non-exposed by means of urine analysis for MA. The urinary MA concentration was suppressed by coexposure to toluene.

The effect of pH on the kinetics of arylsulphatases A and B

The effect of pH on the kinetics of rat liver arylsulphatases A and B is very similar and shows that two groups with pK values of 4.4-4.5 and 5.7-5.8 are important for enzyme activity. Substrate binding has no effect on the group with a pK of 4.4-4.5; however, the pK of the second group is shifted to 7.1-7.5 in the enzyme-substrate complex. An analysis of the effect of pH on the Ki for sulphate inhibition suggests that HSO4-is the true product. A model is proposed that involves the two ionizing groups identified in the present study in a concerted general acid-base-catalysed mechanism.

Chromatographic separation and quantitative determination of the metabolites of di-(2-ethylhexyl) phthalate from urine of laboratory animals

Free, glycine-conjugated, and glucuronide-conjugated metabolites of di-(2-ethylhexyl) phthalate may be stripped from urine with XAD-2 resin, derivatized, and quantitatively analyzed by liquid chromatography on a nitrile column with UV and/or radioactivity monitors. One class of metabolites requires reversed-phase chromatography or gas-liquid chromatography for its resolution. Relative molar responses of the hydrogen flame-ionization detector to these metabolites have been determined. Packed gas chromatography columns (OV-3, OV-210, cyclohexanedimethanol succinate) and fused-silica capillary columns (SP2100 and FFAP) are useful for quantitative analysis under appropriate conditions. The simplest gas chromatographic procedure permitting complete quantitative analysis requires hydrolysis of conjugates, formation of methyl esters of carboxyl groups, butyration of hydroxyl groups and chromatography on OV-3. Typical distributions of di-(2-ethylhexyl) phthalate metabolites in urine from mice, hamsters, and guinea pigs are presented.

3'-phosphoadenosine-5'-phosphosulphate synthesis and involvement in sulphotransferase reactions in the insect, Spodoptera littoralis

1. Synthesis of 3'-phosphoadenosine-5'-phosphosulphate from ATP and 35SO4(-2) was demonstrated by homogenates of gut. Malpighian tubules and fat body of Spodoptera littoralis. 2. The enzyme system was most active in the gut tissue, and was primarily located in the cytosol fraction of the cell. Gut cytosol preparations were used as a source of the 3'-phosphoadenosine-5'-phosphosulphate generating system for more detailed studies. 3. Maximum synthesis required an incubation mixture containing Tris/HCl buffer (pH 7.5), ATP (20 mM), MgCl2 (13.0 mM) and K2SO4 (3 mM). 4. The specific activity of 3'-phosphoadenosine-5'-phosphosulphate synthesizing activity in gut cytosol increased during development of the sixth instar larva, reaching a peak at day 4. A sudden fall in specific activity was observed in the prepupal stage. 5. 3'-Phosphoadenosine-5'-phosphosulphate formation is the rate limiting process in the overall sulphation of p-nitrophenol in the gut cytosol preparations from S. littoralis. 6. It is concluded that the properties of the sulphate-activating system in this insect are similar to those reported for vertebrates.

A variant form of arylsulfatase A in human urine derived directly from the renal pelvis: kinetic and immunological characterization

Arylsulfatase A (aryl-sulfate sulfohydrolase, EC 3.1.6.1) was examined in voided and in nephrostomic urine. A variant form of the enzyme was found in nephrostomic urine, in addition to the minor form, which is the sole component of arylsulfatase A in voided urine. The nephrostomic enzyme differed from the voided urine enzyme with respect to the kinetic parameters, the isoelectric point, heat stability and immunological reactivity. The isoelectric points of the voided urine and nephrostomic enzymes were 4.7 and 5.3, respectively. The nephrostomic enzyme was more heat-labile at 62.5 degrees C than the voided urine enzyme. Although the Km values of the two enzymes with nitrocatechol sulfate as substrate were almost the same, the V value of the nephrostomic enzyme was approx. one-hundredth that of the voided urine enzyme. The molecular weight (almost 130 000) did not differ between the voided urine and nephrostomic enzymes. It was demonstrated by various methods, using IgG antibody against the purified voided urine enzyme, that the nephrostomic enzyme was antigenically distinct from the voided urine enzyme.

Kinetic studies of the phenol sulphate-phenol sulphotransferase of Aspergillus oryzae

Arylsulphatase II of Aspergillus oryzae exhibits both hydrolytic and sulphotransferase activities. The kinetic data suggest the formation of an intermediate covalent enzyme-sulphate complex with transfer of sulphate from donor to acceptor proceeding via a Ping Pong mechanism. The unusual kinetic behaviour when 2-hydroxy-5-nitrophenyl sulphate is the substrate is also consistent with this mechanism.

Urinary oestrogen and plasma human placental lactogen as initial screening tests for a placental sulphatase deficiency

As a result of routine screening of ante-natal patients by urinary total oestrogens and plasma human placental lactogen (HPL) from 35 weeks, a rare placental sulphatase deficiency was indicated which was later confirmed by in vitro studies of placental enzyme activities.

Purification and properties of arylsulphatase B of human liver

1. A purification scheme for an arylsulphatase B from human liver is described. Specificity of purification was achieved by the use of the affinity chromatography on an agrose-4-hydroxy-2-nitrophenyl sulphate derivative. The scheme provides a rapid and convenient method for preparation of a highly purified enzyme. 2. The purified enzyme was examined by isoelectric focusing electrophoresis on polyacrylamide gel and by ultracentrifugation and was found to be catalytically homogenous, with an apparent molecular weight of 50000 and a specific activity of 93.3 units/mg of protein. 3. The kinetic properties of the purified preparation and the effect of various amino acid group-specific reagents on the catalysis of the enzyme are described. The involvement of histidine residues in the active site of the enzyme is suggested. 4. The purified enzyme lost activity rapidly on freezing. The implication of this observation is discussed in terms of a possible dissociation-reaggregation phenomenon induced by cold treatment.

The specific assay of arylsulphatase C, a rat liver microsomal marker enzyme

Conditions based on previous assays with potassium p-acetylphenyl sulphate have been established for the specific assay of arylsulphatase C in rat tissues. The enzyme has optimum activity with 40mm substrate at pH8.0 in the presence of 0.1m-phosphate buffer. Under these conditions arylsulphatase C can be assayed without interference from the other arylsulphatase enzymes present and is useful as a marker for the endoplasmic reticulum in cell-fractionation studies.

Studies on the oestrogen sulphatase and arylsulphatase C activities of rat liver

Detailed studies on the hydrolysis of p-acetylphenyl sulphate and oestrone sulphate by rat liver preparations strongly indicate that arylsulphatase C and oestrogen sulphatase are the same enzyme. Liver is the richest source of both enzymes, which have identical intracellular distributions, being localized mainly in the microsomal fraction. Low oestrogen sulphatase and arylsulphatase C activities were present in foetal liver and these increased at a similar rate after birth. The activities of the enzymes in an ethionine-induced hepatoma were similarly low. Results of heat inactivation, mixed-substrate and competitive-inhibition experiments employing liver microsomal fractions were also consistent with one enzyme being involved. Oestradiol-17beta 3-sulphate was also hydrolysed by microsomal preparations and activity towards both this substrate and oestrone sulphate was inhibited by oestrone and oestradiol-17beta. The physiological significance of this inhibition is discussed.