Purification and properties of a phenol sulphotransferase from Euglena using L-tyrosine as substrate.

A purification procedure based on (NH4)2SO4 precipitation, and chromatography on Affi-Gel Blue, DEAE-cellulose, hydroxyapatite and Bio-Gel P-60 yields a stable 6400-fold-purified active monomeric phenol (tyrosine) sulphotransferase of 26 kDa from W10BSmL, an aplastidic mutant of Euglena gracilis var. bacillaris. The apparent Km for adenosine 3'-phosphate 5'-phosphosulphate (PAPS) is 15 microM (60 microM tyrosine as substrate); adenosine 5'-phosphosulphate is inactive. L-Tyrosine gave the lowest apparent Km (33 microM) (with PAPS at 30 microM), but tyrosine esters, tyrosinamide, L-p-hydroxyphenylglycine and a number of tyrosine dipeptides were also active, with higher Km values. Nitrophenols (m- and p-) and chlorophenols (o-, m- and p-) were active, with higher Km values than for tyrosine. D-Tyrosine was inactive as a substrate, as was D-p-hydroxyphenylglycine and a number of other tyrosine derivatives lacking the carboxy carbonyl or the amino group, or having extra ring substituents or the hydroxy group in the wrong position. Adenosine 3',5'-bisphosphate and tyrosine O4-sulphate, products of the enzyme reaction with PAPS and tyrosine as substrates, showed competitive (Ki = 20 microM) and uncompetitive (Ki = 500 microM) inhibition kinetics respectively. This appears to be the first phenol sulphotransferase to accept tyrosine as substrate. This membrane-bound enzyme may be involved in tyrosine transport as well as detoxification.

Purification and properties of two forms of ATP sulfurylase from Euglena.

Two forms of ATP sulfurylase have been purified to homogeneity from mitochondria (ATPSm) and cells (ATPSc) of Euglena gracilis Klebs var. bacillaris Cori (aplastidic mutant W10BSmL). Both forms are monomeric, ATPSc is 52.3 kDa and ATPSm is 55 kDa. The pI is 7.9 for ATPSc and 5.8 for ATPSm. Therefore, ATPSm binds to DEAE-cellulose at pH 7.4; ATPSc does not. After cleavage by CNBr, the two forms of ATP sulfurylase show different sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns, suggesting that they differ in amino acid sequence. ATPSm is mainly associated with the mitochondrial membrane and ATPSc is mainly soluble in the cells. Both enzymes require similar conditions in the molybdolysis assay, but show different pH optima when sulfate is used as substrate. ATPSc is more sensitive to adenosine 5'-phosphosulfate (APS) inhibition than ATPSm in the SO2-4 incorporation reaction. In the reverse reaction, ATPSc requires much higher concentrations of PPi and MgCl2 to saturate the reaction than ATPSm. The data indicate that the two enzymes are quite distinct and may have different roles in cell metabolism.

Formation of tyrosine O-sulfate by mitochondria and chloroplasts of Euglena.

Mitochondria that have been purified from cells of light-grown wild-type Euglena gracilis Klebs var. bacillaris Cori or dark-grown mutant W10BSmL and incubated with 35SO4(2-) and ATP accumulate a labeled compound in the surrounding medium. This compound is also labeled when mitochondria are incubated with [14C]tyrosine and nonradioactive sulfate under the same conditions. This compound shows exact coelectrophoresis with synthetic tyrosine O-sulfate at pH 2.0, 5.8, and 8.0, and yields sulfate and tyrosine on acid hydrolysis. Treatment with aryl sulfatase from Aerobacter aerogenes yields sulfate and tyrosine but no tyrosine methyl ester; no hydrolysis of tyrosine methyl ester to tyrosine is observed under identical conditions, ruling out methyl esterase activity in the aryl sulfatase preparation. Thus the compound is identified as tyrosine O-sulfate. No tyrosine O-sulfate is found outside purified developing chloroplasts of Euglena incubated with 35SO4(2-) and ATP, but both chloroplasts and mitochondria accumulate labeled tyrosine-O-sulfate externally when incubated with adenosine 3'-phosphate 5'-phospho[35S]-sulfate (PAP35S). Since tyrosine does not need to be added, it must be provided from endogenous sources. Labeled tyrosine O-sulfate is found in the free pools of light-grown Euglena cells grown on 35SO4(2-) or in dark-grown cells incubated with 35SO4(2-) in light, but none is found in the medium after cell growth. No labeled tyrosine O-sulfate is found in Euglena proteins (including those in extracellular mucus) after growth or incubation of cells with 35SO4(2-) or after incubation of organelles with 35SO4(2-) and ATP or PAP35S, ruling out sulfation of the tyrosine in protein or incorporation of free-pool tyrosine O-sulfate into protein. The system forming tyrosine O-sulfate is membrane-bound and may be involved in transporting tyrosine out of the organelles.

A sulphate metabolizing centre in Euglena mitochondria.

We have previously shown that a sulphate activating system is present on the outside of the inner mitochondrial membrane of Euglena gracilis Klebs. var. bacillaris Cori, but efforts to couple this system to ATP produced from oxidative phosphorylation were unsuccessful. In the present work we show that the concentration of Pi ordinarily used to support oxidative phosphorylation in these mitochondria (10 mM) inhibits sulphate activation completely; by reducing the concentration of Pi 10-fold, both processes proceeded normally. Sulphate activation under these conditions is inhibited nearly completely by the uncouplers of oxidative phosphorylation dinitrophenol (0.1 mM) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) (0.2 microM). Sulphate reduction to form free cysteine, most of which appears outside the organelle, and in the cysteine of mitochondrial protein can be demonstrated in the same preparations, is membrane-bound and is inhibited by chloramphenicol (100 micrograms/ml), NaN3 (5 mM), KCN (100 microM); dinitrophenol (0.1 mM) or CCCP (0.2 microM). Digitonin fractionation of the mitochondria into mitoplasts, outer membranes and an intermembrane fraction show that reduction of 35SO4(2-) to form free cysteine and cysteine of protein is located on the mitoplasts; adenosine 5'-phosphosulphate sulphotransferase, the first enzyme of sulphate reduction, is found in the same location. Sulphate activation is highly enriched in the mitochondrial fraction of Euglena; the small amount found in the chloroplast fraction can be attributed to mitochondrial contamination. Thus, in Euglena, sulphate activation and reduction are contained in a sulphate metabolizing centre on the outside of the mitochondrial inner membrane; this centre appears to supply the mitochondrion and the rest of the cell with the products of sulphate activation as well as with reduced sulphur in the form of cysteine. Mitochondria from wild-type Euglena cells and from W10BSmL, a mutant lacking plastids completely, appear to be similar in the properties studied.

Localization of a sulphate-activating system within Euglena mitochondria.

Intact mitochondria, obtained from Euglena gracilis Klebs var. bacillaris Cori mutant W10BSmL, which lacks plastids, and purified on Percoll density gradients, form adenosine 3'-phosphate 5'-phosphosulphate from sulphate. The optimal conditions include addition of 17 mM-Tricine/KOH, pH 7.6, 18 mM-MgCl2, 250 mM-sucrose, 5.66 mM-sodium ADP (or 0.94 mM-sodium ATP), 1 mM-K2SO4, carrier-free 35SO4(2-) (32.1 microCi) and 1.0 mg of mitochondrial protein in a total volume of 2.65 ml and incubation at 30 degrees C. Experiments with the inhibitor of adenylate kinase P1, P5-di(adenosine 5'-)pentaphosphate indicate that ATP is the preferred substrate for sulphate activation; ADP is utilized by conversion into ATP via adenylate kinase. ATP sulphurylase, adenylylsulphate kinase (APS kinase) and inorganic pyrophosphatase constitute the sulphate-activating system; ADP sulphurylase is undetectable. Fractionation of Euglena mitochondria with digitonin and centrifugation allowed the separation of outer-membrane vesicles and mitoplasts as judged by electron microscopy and selected enzymic markers. The detergent-labile association of the sulphate-activating system with the mitoplasts (similar to that of adenylate kinase), the fact that most of the adenosine 3'-phosphate 5'-phosphosulphate formed by intact mitochondria is found in the surrounding medium, and the ease with which nucleotide substrates reach the activating system in intact organelles, suggest that the enzymes of sulphate activation are located on the outer surface of the mitochondrial inner membrane.