VOL. 22 (1956) PRELIMINARY NOTES 203

r6versibles, l 'irr6versibilit6 de la t ransformat ion est assur6e dans les t issus par le fair que le TPN s 'y t rouve essentiellement sous sa forme r6duite et le D P N sous sa forme oxyd6e 4.

L ' in tervent ion de ce m6canisme dans les t ranches et les extrai ts de v6sicules s6minales de mou ton est montr6e par le fair que le glucosone et la glucuronolactone inhibent compl~tement la t ransformat ion du glucose en sorbitol et fructose par ces pr6parat ions. De plus les extrai ts trait6s par l '6thyl~nediaminet6traac6tate forment encore du sorbitol mais pas de fructose A par t i r de glucose.

Malgr6 que le glucosone soit trbs facilement r6duit en fructose, aucun des rdsultats obtenus jusqu '~ pr6sent n ' indique qu'il puisse ~tre form6 ~ par t i r de glucose et servir ainsi d ' interm6diaire dans la t ransformat ion 6tudide.

Quant ~ la r6duction de la glucuronolactone en gulonolactone elle est consid6rde par ISHER- WOOD et coll. ~ comme une 6tape probable de la biosynthbse d'acide ascorbique £ part i r de glucose.

Ce travail a 6t6 subsidi6 par le Centre National de Recherches Enzymologiques, l ' Ins t i tu t Inter- universitaire de Sciences Nucl6aires et les Lilly Research Laboratories.

Laboratoire de chimie physiologique, Universit~ de Louvain, Louvain (Belgique)

1 T. MANN ET U. PARSON, Biochem. J. , 46 (195 o) 44 o. 2 H. G. WILLIAMS-ASHMAN ET J. BANKS, Arch. Biochem. Biophys., 5 ° (1954) 513 . 3 H. G. HERS, Arch. intern, physiol, et biochim., 64 (I955) 133. 4 G. E. GLOCK ET P. McLEAN, Biochem. J. , 61 (1955) 388- 5 F. A. ISHERWOOD, Y. T. CHEN ET L. W. MAPSON, Biochem. J., 56 (1954) I.

* Associ~ du FNRS

H. G. HERS*

Regu le 3 ° juillet 1956

Effects of irradiation in v/vo on bacterial deoxyribonucleic acid*

We have been s tudying by the flow birefringence technique E. coli DNA irradiated in vivo by X- rays. No changes were found in the physical properties as the result of doses of io,ooo r. This dose is sufficient to inactivate a large fraction of the bacterial populat ion and to alter markedly the physical properties of DNA irradiated in vitro.

5oo ~0oo ~ o o z0oo 2*oo 3ooo ~ m o o o m o

VEL0CtTY SnAOteNV LN SEC "~ Fig. I. Ext inct ion angle vs, velocity gradient. Measurements were made in 0.2 M NaC1 at a DNA concentrat ion of o.6 mg/ml. I-A and 2-A received IO,OOO r in vivo. I-A was extracted immediately after irradiation; 2-A was incubated for two hours at 37°C before extraction. I-B and 2-B are

the corresponding unirradiated controls.

* This article is based on work performed under Contract No. AT-o4-I-GEN-I2 between the Atomic Energy Commission and the Universi ty of California at Los Angeles.

204 PRELIMINARY NOTES VOL. 9.9. ( i 956 )

E. coli was grown on nutr ient agar for 24 hours at 37 °. The ceils were harvested, washed, and collected in the centrifuge. Packed ceils were spread in a i to 2 m m thick layer and exposed to io,ooo r delivered by a beryllium window tube operated at 5 ° KVP. A 0.25 m m A1 filter was used to insure a reasonably uniform dose th roughout the bacterial layer 1. In one exper iment the DNA was extracted immediately after irradiation. In a second exper iment the irradiated bacteria were first t ransferred to nut r ient bro th and incubated at 37°C for two hours; then the DNA was ex- tracted. In both experiments half the harvested cells were used as controls. The yields and the ultraviolet spectra of the irradiated DNA were not significantly different from those of the un- irradiated controls.

Fig. I. presents the extinction angle vs. gradient curves for two preparat ions irradiated in vivo and the corresponding controls. The curves are quite similar to those published previously for E. coli DNA 2 and for other good DNA preparat ions 3. No significant differences between the irra- diated and control samples are apparent despite the very high sensitivity of the flow birefringent technique in detecting small differences in the length distr ibutions of the preparat ions a.

! i l t

i I

i ~ V / I I I

800 IGO0

0 I A

Q IB

/x 2A • 2 a

I

Z ~ " " - I A AFTER LO~OOOr IN VITRO i

, j i

I ] t i

, t l 2400 3200 4000 4800 5600 6 4 0 0

VELOCLTY GRADIENT IN SEC "1

Fig. 2. Birefringence vs. velocity gradient. Measurements were made in 0.2 M NaC1 at concentra- tions of 0.i to 0.2 mg/ml. I-A and I-B, 2-A and 2-B are the same samples shown in Fig. I. The

lowest curve shows the effect of i0,000 r in vitro on sample I-A.

Fig. 2 shows the corresponding values of the birefringence vs. gradient. (The values of the birefringence were normalized by dividing by the concentrations.) As can be seen no significant changes were induced by the in vivo irradiations. By contrast I0,000 r applied in vitro reduced the birefringence of the solutions by a factor of two. The results of such an irradiation are shown in the bo t tom curve of Fig. 2.

These results indicate tha t in vivo E. coli DNA is well protected from the indirect effects of X-rays. Similar results have been found by DREW 4 for the pneumococcus t ransforming principle activity. I n vitro, however, it has been found very difficult to protect t ransforming principle against the indirect effect of X-rays. 5 The very interesting question is raised by these results of the actual s tate of DNA in vivo.

Department o/Radiology, School o[ Medicine and Atomic Energy Project, University o[ Cali/ornia, Los Angeles, Call[. (U.S.A.)

AMOS NORMAN JOHN \V. ROWEN

1 A. NORMAN AND M. A. GREENFIELD, Radiation Research, 3 (1955) 407 • 2 j . W. ROWEN AND A. NORMAN, Arch. Biochem. Biophys. , 51 (1954) 524. 3 M. GOLDSTEIN AND M. E. REICHMANN, J . A m . Chem. Soc., 76 (1954) 3337. 4 R. M. DREW, Radiation Research, 3 (1955) 116.

H. EPHROSSI-TAYLOR AND IR. LATARJET, Biochim. Biophys. Acta, 16 (1955) 183.

Received July 23rd, 1956