DISSOCIATION OF THE DEHYDROGENATING AND TRANSHYDROGENATING ACTIVITIES OF THE jc~-HYDROXYSTEROID DEHYDROGENASE OF RAT

LIVER BY f344ERCAPTOETHANOL AND TESTOSTERONE

Samuel S. Koide

Division of Clinical Investigation Sloan-Kettering Institute

New York, New York

iieceived Movt:nber 5, lY63

ABSTRACT

A preparation of 3CZ-hydroxysteroid dehydrogenase obtained from the soluble fraction of rat I iver was treated with B-mercaptoethanol or testosterone and further purified by Cy-alumina adsorption and ammonium sulfate precip i tat ion. Although the dehydrogenating and transhydrogena- ting activities were inhibited by B-mercaptoethanol and testosterone, the transhydrogenating activity was inhibited to a relatively greater extent. The inhibition effected by testosterone was partially reversed on subsequent purification by ammonium sulfate precipitation, whereas that by f+mercaptoethanol remained substantial ly unchanged.

The part ial purification of 3CShydroxysteroid dehydrogenase (D-

hydroxysteroid-NAD(P) oxidoreductase, EC 1.1.1.50) from the soluble

fraction of rat I iver was recently reported (1). The dehydrogenat ing and

transhydrogenating activities were not separated during any of the steps

of purification utilized. There was, however, considerable variation in

the ratio of NAD- to NADP-dehydrogenat ing act ivit ies with some of the

enzyme preparations. It was observed that when @-mercaptoethanol was

added to the isolation medium the activity and recovery of the 3~

hydroxysteroid dehydrogenase were decreased. The result ing enzyme prepara-

t ion possessed predominantly NADP-dehydrogenat ing act ivity. In an earlier

report (2)) testosterone was also found to inhibit primarily the trans-

86 STEROIDS 3:1

hydrogenat ing act iv i ty. In this study, a preparat ion of a 3@hydroxy-

steroid dehydrogenase was treated with @-mercaptoethanol and testosterone

and partially purified by CT-alumina adsorption and (NH4)2S04 precipitation

in order to dissociate the transhydrogenating from the dehydrogenating

activities.

METHOD

The initial two steps in the isolation of 3O+hydroxysteroid dehydroge- nase were performed as previously described with sl ight modifications (1). All procedures were performed at 0-4oC. in summary, livers from adult male rats were excised, homogenized in 0.1 M potassium phosphate buffer, pH 7.5, centrifuged at 13,000 x g for an hour and fractionated with the addition of (NH41 2SO4. The enzyme preparation precipitated between 0.5 to 0.7 satura- tion was dissolved in Medium A (0.01 fl potassium phosphate buffer, 20% glycerol, final pH 7.5). The preparation was dialyzed against several changes of Medium A unt ii the dialyzing medium gave a negative test for ammonia with Nessler’s reagent. The dialyzed preparation was centrifuged at 27,000 x g for 15 minutes.

The enzyme preparation (SO mg protein/ml.) was divided into 3 parts. To one sample an equal volume of 0.1 M potassium phosphate buffer, pH 7.5 was added (control). To the second sample, an equal volume of a solution containing 0.01 M ~-mercaptoethanol, 0.1 M potassium phosphate buffer, pH 7.5 was added. To the third sample an equal volume of 0.1 M potassium phosphate buffer, pH 7.5 and testosteron dissolved in 0.2 ml. of dioxane to give a final concentration of 5 x 10’ g M wera added. A second experi- ment was conducted util izing 0.1 M glycine-NaOH buffer, pH 9.5 in place of potassium phosphate buffer. Samples were removed at various time intervals and assayed. After 6.5 hours the enzyme preparation was diluted with 40% glycerol solution to give a protein concentration of 20 mg./ml. Cy-alumina sol ut ion (20 mg./ml .) was added to the enzyme preparat ion to give a protein to gel ratio of 1:l. The mixture was stirred for 15 min. and centrifuged at 10,000 x g for 10 min. The Cy-alumina was resuspended in a solution containing,20% glycerol, 0.5 N phosphate buffer, pH 7.5 and centrifuged at 10,000 x g for 10 min. The extraction was repeated and the extracts were pooled. A small amount of enzyme could be recovered by a third extract ion with a solution of 1 M (NH4)2S04 in 20% glycerol, pH 7.5.

The supernatant solutions were dialyzed overnight against a saturated (NH4)2SO4 solution in 20% glycerol adjusted to pH 7.5 with NH4OH and centri- fuged at 27,000 x g for 15 min. The precipitate was dissolved in a minimal volume of Medium A. The supernatant solutions were dialyzed overnight

against saturated (NH4)2SO4 solution in 10% glycerol adjusted to pH 7.5 with NH40H, and centrifuged at 27,DOO x g for 15 min. The precipitate was dissolved in a minimal volume of Medium A.

The NADP-dehydrogenating activity was assayed in a total volume of

Jan. 1964 STEROIDS 87

3 ml. containing 200 umoles of buffer, 0.5 umole NADP and 1.S mg. of enzyme. The NAD-dehydrogenating activity was assayed in a total volume of 3 ml. containing 200 umoles of buffer, 1 umole NAD and 3 mg. of enzyme. The reaction was initiated by the addit ion of 35 pg. of androsterone dissolved in 10 ul. dioxane to the reaction cuvette. The cant rol cuvette conta i ned all ingredients except the steroid. The t ranshydrogenat ing system con- tained 0.6 Kornberg unit of glucose 6-phosphate dehydrogenase, 5 umoles of disodium glucose 6-phosphate, 5 umoles MgC12, I umole NAD, 0.02 umole NADP, 9 mg. of enzyme, 200 umoles of buffer in a total volume of 3 ml. After 5 min. of equil ibration the reaction was initiated by the addition of 7 ug. androsterone dissolved in IO ~1. dioxane to the reaction cuvette. The con- trol cuvette contained all ingredients except the steroid. The changes in absorbancy were measured with a Cary recording spectrophotometer equipped with a 0.1 absorbancy sl idewire attachment, employing a 1 cm. 1 ight path at 340 rr+.~, 22O-23O C. The rate of reaction was calculated from the initial I inear portion of the graph. Trip1 icate determinations agreed within 5%. One unit of all three activities represents a change in absorbancy of O.OOl/min.

The glucose 6-phosphate dehydrogenase was dissolved in 1% crystalline bovine albumin and was dialyzed against several changes of 0.01 M tris-HCI buffer, pH 7.5 until the dialyzing medium gave a negative test for ammonia with Nessler’s reagent.

RESULTS AND DISCUSSION

The dehydrogenat ing and transhydrogenat ing act iv it ies were tested in

various buffers to determine the optimum pH and buffer systems. The

greatest act iv i t ies of NAD-dehydrogenat ion and t ranshydrogenat ion occurred

near pHs 8 and 7.5, respectively, which agreed with that reported in the

1 iterature by others (3,4,5). The NADP-dehydrogenat i ng act iv i ty, however,

was maximum at pH 9.5 (Table I).

We have confirmed the report of Baron and co-workers (5) that bivalent

anions stimulated the NAD-dehydrogenat ing and transhydrogenat ing activities

and had no influence on the NADP-dehydrogenating activity. We have

observed that the NAD-dehydrogenat ing activity was greater when potassium

phosphate buffer, pH 7.5, was used in the assay system than systems con-

taining various concentrations of (NH4)2S04 in tris-HCl buffer, pH 7.5

(Table I I). Furthermore, the addition of various increments of (NH4)2SO4

88 STEROIDS 3:l

TABLE I NAOP-DEHYDROGENATING ACTIVITY OF ~c+HYOROXYSTEROID OEHYDROGENASE IN VARIOUS BUFFER AND pH’S.

Buffers Specific Activities (units/mq. protein)

pH 9.0 . 10.0 IO.5

Sodium pyrophosphate 6.6 9.4 3.7 --

Sodium carbonate-bicarbonate -- 7.0 1.6 0.2

Glycine-NaOH 7.5 10.0 9.9 2. I

The enzyme preparation used was obtained following a~nium sulfate precipitation and dialyzed against 0.01 M tris-HCl buffer, pH 7.5.

TABLE I I EFFECTS OF VARIOUS CONCENT~TIONS OF AMMONIUM SULFATE ON THE OEHYOROGENATING AND T~NSHYDROGENATING ACTIVITIES OF ICY-HYOROXYSTEROIO DEHYOROGENASE.”

Concentrat ion of (M) Specific Activities (units/mg. of protein)

(NH4) $04 NAO-Oehydrog. NADP-dehydrog. Transhydrog.

A B A 5 A B

L:Z ::;: I.5 1.5 1.7 1.8 0.4 0.05 0.03

i:: ::: 1.5 1.5 1.6 1.7 k:: 0:4 0.4 0.3

4.0 3.7 1.6 1.8 0.4 0.4

:::, 3.3 2.7 1.3 1.4 I.6 1.5 0.3 0 0.4 0. i

* The 3Whydroxysteroid dehydrogenase preparat ion and glucose &phosphate dehydrogenase were dialyzed for 24 hrs. against 0.01 M tris-HCI buffer,

pH 7.5. The dehydro enat ing and t ranshydrogenat i ng act iv it ies were assayed in 6.6 x 10’ 9 M potassium phosphate (A) and tris-HCI buffers,

PH 7.5 (8). Aliquots of 1 M (NH4)2S04 solution adjusted to pH 7.5 with dilute NH4OH was added to give the appropriate concentrations.

to the potassium phosphate buffer assay system had an inhibitory influence

on the NAD-dehydrogenat ing act iv i ty. The t ranshydrogenat ing act iv i ty was

the same with tris-HCI buffer, pH 7.5, containing 3.3 x 1W2 M (NH4)2SD4

Jan. 1964 STEROIDS

and with phosphate buffer, pH 7.5. In this study we have assayed the

NAD-dehydrogenat ing and t ranshydrogenat ing act iv i t ies in phosphate

buffer at pH 7.5 and the NADP-dehydrogenating activity in glycine-NaOH

buffer, pH 9.5.

The result of one of the representative experiments of f3-mercapto-

ethanol and testosterone treatment at pH 7.5 and 9.5 is shown in Tables

III and IV. The effect of @mercaptoethanol was more pronounced at pH 9.5

than pH 7.5. The inhibition of the dehydrogenating and transhydrogenating

activities with @mercaptoethanol progressed with time, whereas the block

effected by testosterone remained rather constant throughout the 6.5 hr.

period. The transhydrogenat ing activity was most sensitive and the NADP-

dehydrogenat ing activity was least sensitive to B-mercaptoethanol or

testosterone treatment.

All three activities of the control sample at pH 7.5 increased

slightly with time (Table III). This finding remains unexplained although

it could conceivably be caused by the greater concentration of phosphate

in the mixture system (0.05 M) over that in the init ial enzyme preparation

(0.01 M). In contrast the NAD-dehydrogenating activity of the control

sample decreased gradually in glycine-NaOH buffer at pH 9.5, whereas the

NADP-dehydrogenat ing and t ranshydrogenat i ng act iv it ies remained rather

constant. This gradua I decrease in NAD-dehydrogenat ing act iv i ty at pH 9.5

occurred also with sodium pyrophosphate-sulfate and potassium phosphate

buffers.

The proport ion of the dehydrogenat ing and transhydrogenat ing activities

of the control preparation were relatively constant following Cy-alumina

adsorption and (NHb)zSOb precipitation (Table IV). In contrast, the

B-mercaptoethanol-treated preparation showed predominantly NADP-dehydrogena-

90 STEROIDS 3:l

TABLE I I I RATES OF DEHYDROGENATION AND TRANSHYDROGENATION MEDIATED BY 3a-HYDROXYSTEROID DEHYDROGENASE AT VARIOUS TIME INTERVALS FOLL(XJING B-MERCAPTOETHANOL AND TESTOSTERONE TREATMENT.*

Time (hr.) Samples Specific Activities (units/mg. of protein)

NAD-dehydrog. NADP-dehydrog. Transhydrog.

A B A B A B

0.5 Control $-SHE Testosterone

3.0 Control B-SHE Testosterone

6.5 Control B-SHE Testosterone

6.3 g-6

::t; 5-o 5.4

8.5 8.9

2:; 0.8 5.8

9.2 6.9

;:; t::,

15.2 18.4 14.9 9.6 1:::

18.5 20.7 10.2 6.2 12.8 12.3

18.9 20.7 1.0 0.7 8.9 5.4 0.08 o

14.0 12.7 0 0

0.6 0.7 0.3 0.02

0 0

0.8 0.7 0.2 0

0 0

* The procedure and assay systems are described in the text. The experiment was performed with potassium phosphate buffer, pH 7.5 (A) and with glycine-NaOH buffer, pH 9.5 (B). The NAD-dehydrog- enat ing and transhydrogenat ing activities were assayed in potassium phosphate buffer, pH 7.5 and the NADP-dehydrogenating activity in glycine-NaOH buffer, pH 9.5. The abbreviation B-SHE is @-mercaptoethanol.

ting activity and varying ratios of NAD- to NADP- dehydrogenat ing act iv i t ies

(Table V) . A low residual transhydrogenating activity was observed with

the (NH4)2S04 precipitated preparation. It is known that @-mercaptoethanol

reduces disulf ide 1 inkages (6) - It would appear, therefore, that intact

disulfide bonds are essential for the NAD-dehydrogenating and transhydrogena-

ting activities.

We have shown earl ier that a,@-unsaturated 3-ketosteroids inhibit

the dehydrogenat ing and t ranshydrogenat ing act iv i t ies mediated by 30+

hydroxysteroid dehydrogenase (2). The t ranshydrogenat ing act iv i ty was

found to be more sensitive to the inhibitory influence of testosterone

than the dehydrogenating activities. The ratios of the NAD- to NADP-

Jan. 1964 STEROIDS 91

TABLE IV SPECIFIC DEHYDROGENATING AND TRANSHYDROGENATING ACTIVITIES OF f3-MERCAPTOETHANOL-AND TESTOSTERONE-TREATED 3a-HYDROXY- STEROID DEHYDROGENASE FOLLOWING PARTIAL PURIFICATION.*

Steps of Purif icat ion Samoles

Activity (units/mg. protein) NAD-dehy. NADP-dehy. Transhy.

A B A B A B

1. Cy-Alumina Cont r-01 7.8 11.2 20.0 18.2 0.6 0.9

B-mercaptoethanol 0.8 0.1 5.5 3.3 o Testosterone 6.7 8.5 16.7 13.0 0 0006

2. (NH4) $04 Cont ro I 4.9 5.9 14.2 13.4 0.5 0.7 Precipitation B-mercaptoethanol 0.4 1 .O 4.7 3.4 0.02 0 a. in 20% glycerol Testosterone 4.0 3.6 10.5 9.2 0.02 0.02

b. in 10% glycerol Control 13.2 13.9 31.6 23.7 2.1 1.2 B-mercaptoethanol 1.6 2.4 24.0 9.7 0.2 0.02 Testosterone 8.8 12.8 27.8 20.5 0.6 0.5

* The procedure and assay systems are described in the text. The enzymes preparations from the previous experiment (see Table I I I) were partially purified by Cy-alumina adsorption and (NH4)2SO4 precipitation. A and B refer to the experiment performed at pH 7.5 and 9.5, respectively.

TABLE V PROPORTIONS OF NAD-DEHYDROGENATION: NADP-DEHYDROGENATION: TRANSHYDROGENATION.*

Steps Cont ro I B-Mercaptoethanol Testosterone

I.

2.

C7-A 1 urn i na A 1:2.6:0.08 1:6. g:o 1:2.5:0 Adsorption B 1:1.6:0.08 I :33:0 1:1.5:0.01

(NH4) 2SO4 Precipitation a, In IO% glycerol A I :2.g:o.i I: 12:0.05 1:2.6:0.005

B 1:2.3:0.1 1:3.4:0 I :2.5:0.006

b. In 20% glycerol A I :2.4:0. I6 1:15:0.02 1:3.2:0.07 B 1:1.7:0.09 1:4.0:0.008 1:1.6:0.04

* Approximate proportion of the activities from Table IV. A and B refer to the experiments performed at pH 7.5 and 9.5, respectively (See Tables III and IV).

STEROIDS 3:l

dehydrogenating activities were similar to those of the control

preparat ion (Table V). The inhibitory influence of testosterone on the

transhydrogenat ing activity persisted even after Q-alumina adsorpt ion

and (NHb)2SOb precip itat ion of the enzyme preparations in 20% glycerol.

The inhibition was substantially reversed in the fraction precipitated

with (NHI+)~SOL, in 10% glycerol (Table IV). It would thus appear that

the inhibition induced by testosterone is partially reversible and not

due entirely to a denaturation of the enzyme in contrast to p-mercapto-

ethanol treatment.

The Whydroxysteroid dehydrogenase from the soluble fraction of

rat 1 iver was partially purified by Tomkins (3) and Hurlock and

Talalay (4). They concluded that the enzyme was probably a dual

pyridine nucieotide-1 inked dehydrogenase. Hurlock and Talalay (4)

further postulated that the transhydrogenation initiated by Whydroxy-

steroid was mediated by the dehydrogenase. In this study we have obtained

with @mercaptoethanol treatment an enzyme preparation possessing markedly

diminished transhydrogenat ing and NAD-dehydrogenat ing act iv it ies, but

retaining substantial NADP-dehydrogenating activity (Tables III and IV).

The results of the present study still leave unanswered the

question whether the transhydrogenase is distinct and separate from the

dehydrogenase. Although the proport ions of the three activities were

markedly altered by p-mercaptoethanol and testosterone treatment and the

transhydrogenating activity was inhibited to a greater extent, the three

activities increased upon subsequent purification (Table IV). Further-

more, we were unable to separate the dehydrogenase and transhydrogenase

on partial purification of the j@hydroxysteroid dehydrogenase (I).

These observations support the hypothesis that the @+hydroxysteroid

Jan. 1964 STEROIDS 93

dehydrogenase possesses transhydrogenat ing activity which is stimulated

by the steroid. Hut-lock and Talalay (4) postulated that the mechanism

of the hydrogen transfer is dependent upon the X.+hydroxysteroid acting

as a coenzyme in an alternating oxidation-reduction of the 3Cz-hydroxyl

group. The finding of a marked variation in the ratios of NAD- to NADP-

dehydrogenating activity and to transhydrogenating activity following

f3-mercaptoethanol and testosterone treatment suggests other mechanisms.

Th is work was supported by a Pub1 ic Health Service Research Career program award No. I-Kj-AM-5517-01 from the National Institute of Arthrit is and Metabol ic Diseases and Grant C-3808 from the National Cancer lnst itute, USPHS. The author is grateful to Dr. R. W. Rawson and Dr. M. Sonenberg for their interest in this study and to Miss M Torres for technical ass istance.

REFERENCES

1. Ko de, S.S., ARCH. BIOCHIM. BIOPHYS. 101, 278 (1963). 2. Koide, S., Chen, C., and Freeman, S., BIOCHIM. BIOPHYS. ACTA 63,

186 (1962).

2: Tomkins, G.M., J. BIOL. CHEM. 218, 437 (1956). Hut-lock, B., and Talalay, P., J. BIOL. CHEM. 288, 886 (1958).

5. Baron, D.N., Gore, M.B.R., Pietruszko, R., and Williams, D.C., BIOCHEM. J. 88, 19 (1963).

, 0. Peters, R.A., and Wake1 in, R.W., BIOCHEM. J. 43, 45 (1948).

ACKNOWLEDGEMENT