Document oe5zpkzdNb5RN6J1dM4e9Oq9X

1 -1 ,4 ^ V 4 X *V 4 *.4 ; I- l i W * A- _-r. VOL- 216. OCTOBER 21. 1967 227 , ;; terminated and the completed chain released ^tlie ribosomc-iRNA complex to which it is bound he iRNA molecule carrying the last amino-acid rporated. There must be a mechanism for reading d.ain terminating codon (three codons UAA, UAG, . I'GA can code for chain termination) and cleaving lost peptidyl-fRXA bond. In Biochem. Biophys. ..Comm,, 2S, 773 (1067) he describes an experimental tan devised to give a rapid assay for chain terminas.andin Proc. i'S Nat. Acad. Sci., 53, 1144 (1967) reports the discovery of an enzyme required for rnmation. Hie assay for termination employs the RX A from sjuber mutant of tlie coat protein gene of the RNA (.((riophage i?17. This mutant has an amber codon, AC, at the position of the sixth amino-acid, a gluta- residue, in the Ii 17 coat protein molecule. In a 3 free system the mutant RNA directs the synthesis a small X-terminal peptide of the coat protein with v sequence X-formylmct-ala-scr-aspn-phe-thr; the xt amino-acid in the coat protein is glutamine, but kIi the mutant RNA the amber codon causes pro cure termination of synthesis and Die release of the 'sapeptide. The great virtue of this system is that 'unterminated peptide still attached to the pcptidyl\A can be distinguished from the terminated peptide 'ased from the IRXA and the amounts of each .'mired. Furthermore, starving the system for any one f the six amino-acids in the peptide arrests the trans ition machinery before it reaches the UAG codon so nnination can be controlled. Exploiting this procedure, Capecchi isolated a v.mplex of ribosome, mRNA and pentapeptidc attached by the phenylalanyl (RNA simply by starving for threonine. With this he has been able to define the conditions necessary for termination; incubating the complex under suitable conditions with or without threonine or supernatant enzymes showed that to'get release it- is necessary but not sufficient to complete the peptide by incorporating threonine and that release is not solely dependent on the transfer enzymes required to move the ribosome from the threonyl codon to the UAG terminating codon. Release docs, however, depend upon the presence of a supernatant factor. This factor, with a molecular weight of between 40,000 and 50,000, sediments between 3-5S and 4'5S. Because its releasing activity is not affected by RNase, it cannot be an RNA-protein complex. Apparently the substrate of the release enzyme is the ribosomc-niRNA-peptidyl (RNA complex so that it must act directly at the ribo some and not cleave the (RNA from pcptidyl-lRXA already released info the supernatant, which was the other possibility. Capecchi does not yet know whether the release enzyme works alone or in conjunction with other factors, in particular a hypothetical chain termination <RXA which reads the termination codon but docs not carry an amino-acid. Many people, including Capecchi, have searched in vain for such a iRNA species, and although negative results can never exclude the possibility that such (RXA exists it is reasonable to think about alternative models in which the terminating codons are read cither by the ribosome or the release enzyme or in which nonsense codons function simply because they cannot be read at all. Further characterization of the release enzyme could well deckle the issue. */ f -y ! ^ ' -- . f ri ) -X 1 : *i 3 f4 4 .* A v Ch lorinated Hydrocarbons in British Wildlife *7 ' p- C. holmes H. SIMMONS !-0'G. TATTON Union0'7 'lV,e Governme Polychlorobiphenyl compounds have been detected in British wildlife. In birds' livers and eggs they are often in greater quantities than organochlorine pesticide residues. Polychloro. biphenyls are known to be toxic, and their detection in wildlife raises the question of the adverse effect they may have. EN "iN birds' eggs or tho livers of British wildlife tiro ,.t "Jnc'd by g.is-liquid chromatography (GLC) using ^on'Mpuue detection, peaks coiTcsponding to such thep200TM01'110 Pesticides as BHC, dieldrin and DDT, and ^,n A ^dabulites and breakdown products, often appear 10 ^mltniit chromatograms. These peaks sometimes 'ltd <T^ am'Junts which are significant from a toxicolo^ 'Pint of view, but the sensitivity of modern instni- ,jf* a'*o enables completely insignificant amounts to be 'f- Analysts concerned with tho determination of hj?,yic"'onile pesticides in wildlife, however, lmvo long (ijwl a"',.rc that it is not unusual for an additional seiies c ninn>" as ten peaks, corresponding to unidentified Lj 'w<io, also to appear on tlieso chromatograms'-*. known of the stmetnro and origin of these coin ' Ur--S but Roburn' established that they are organo- chlorino in nature, with a substantial chlorino content, and consequently possess electron-capturing properties. On silicone or `Apiczon' CLO columns, tho series of peaks for tlieso compounds normally begins at tlie point' at which pp'-T.DE and pp'-DDT arc emerging from tho columns and extends, in terms of retention times, to four or five times that of jip'-DDT,'which is the last of the commonly occurring pesticides to omorgo. Beforo examination by GLC, samples linvo normally been subjected to a fairly rigorous clonn-up procedure, such as tlint of do Faubcrt Maunder cl ah%, which includes a dimcthylformamide-hoxano partition and passage through n column, of prepared alumina. Bceauso these unknown compounds are similar in naturo and properties to tho organochlorine pesticides, they uko pnss through. this and similar clenn-up procedures; consequently, they S' tf . . 1- -u. ' ** t ,. * * *- . :-D '* i < :.'-c-n4 3 .4 ,t 1 J > .5 :1 -i it * > <'' ,* :' . .1 2 DEPOSITION fD EXHIBIT omcI WATER PCB-SD0000038840 ' *T /* -*-V ; * -t ;# ' i t ~i J A AJ f 'i 226 NATURE. VOL. 216. OCTOBER a, Mature often interfere seriously with determinations of yp'-TDE and pp'-DDT in wildlife because of overlapping of tho chromatographic peaks. Suitablo procedures have been devised to overcome this difficulty of interfering peaks. P' k One mothod is to effect a better resolution of these particular peaks by choico of a suitable stationary phase for GLC*. Anotlior method, which also demonstrates the presence of these compounds in the sample, is tho use of a preliminary thin-layer chromatographic treatment'. The cleanod-up extracts are examined on silica gel chromatoplates using a 1 per cent solution of acetone in hexane as mobile phase*. Spots corresponding to the ytt J-7S {01 *31 lit Sri ?#* l-tl j'10 . y y-UL 4 .corTdead, compounds can then be found at Rp values between 0'8 and 1-0, whereas tho com monly occurring organocblorine pesticides and their metabolites produce spots of lower Rp values. A similar separation can also be '-yen ,,f port he -Valid h tlmy1 shown with roverso phaso paper chromato graphy* whereby tho unknown compounds ,'Vms. J move only a very short distance from the ioinical base lino compared with tho pesticides and their metabolites. Gas-liquid chromatography using dual Vp,e cl- '^ifts in t stance, channel detection systems with separate eleetron-capluro and flamo-ionization detec tors has also been used to demonstrate the presence of largo amounts of weakly electron capturing niatorial, in addition to known `-ytrin by r, \ num i sh B i this la rjtheke pesticide residues, in the eggs of oyster catchers (Haemalopus ostralegus)'. Exporicnco in this laboratory has shown yon of til . Vtory i | ijvcever, that those compounds occur most frequently and in the largest proportions in ttic livors. "tat and eggs of birds, particulnrly terreslrial jn-so com ,;,d in tl go such predators such as spiurowhawks (Acciviier and kestrels (Falco tinnuncuh/s) and wry smal u cows i -marine loaders such as guillemots (Uria asrkedly aalge) and kittiwakes (Kissa triuactyla); :.ihave ii ftiby also commonly occur in freshwater fisTn We have detected small amounts m human.mid animal fat samples, but less .frequently and in much smaller proportions Fig. 1. Ga>-llqtil<l chromatogram of (n) extract of kestrel liver and (M a cominnrii: polychtorobiphenyl resin. than in avian samples. _ A similar series ot chromatographic peaks lias been properties. In tho prescribed extraction and GLC coi.*. 1 i l r* observed by Holden'"'11 when examining extracts of seals tions, those mixtures produce a series of chromalograp- >. U C and fish taken in Scottish waters. Ho found that the peaks peaks of tho typo in question. F( given by the extracts of fresh and sea-water fish represen . Tho compounds occurring in British wildlife cornspyf t/ ted fairly love concentrations, but those given by extracts to tlio more highly chlorinated biphenyl compounds r.i:i/-| 'p c gD of seal blubber corresponded to much Inrgor proportions, than tho moro liglitly chlorinated types. These Infrij' ` ` of the order found by this laboratory in birds' eggs. chlorinated biphenyls also occur to some extent in eri Uarversicy Despite considerable curiosity about t lie identity of the-se compounds, littlo progress has been nmdo in identifying them, but there 1ms long been a general supposition that they were cither further breakdown or condensation reten-tion ti.mes occurring in Britis-h wildlife arc hJ p\i'-'vT -.irrjp1orllo%- products of tho organochlorino pesticides or possibly chlorinnted polychloroterphcnyl compounds. i \mi i10r. loose compounds of those with natural products such as Fig. la shows the gas-liquid chromatogram f`-'ifs.ihphei protein matter. extract from a kestrel liver. Tho peaks correspondin' | tj ot|lel Jenson, however, succeeded in identifying a series of pp'-DDE (<M3 ng), bet-a-BHC (0-33 ng) and gamma t; I - Quasars) such peeks ns corresponding to polyolilnrohiphenyl com (0 03 ng) nro labelled. Tho other peaks form the sc* j ^ likely pounds, in 200 pike taken in diffeicnt parts of Sweden, referred to abovo and until now would have been rope.-1l,j.0 jyr and in an eaglo1*. We linvo now been ablo to show that simply as "unknown organoehlorine compounds T npernov. tho long retention time compounds occurring in British corresponding to any known pesticide or its metabh,.' pi^rgy, n wildlife are also polyclilorohiplienyl compounds. Fig. 16 shows tho analogous chromatogram of a coar'-1 tiocceler Polychlorinated biphenyl 1ms been in common commer ciul polyclilorohiplienyl resin. So far as retention I'^f Irionoutu cial uso for some time as n plasticizer in paints, resins and plasties. It also 1ms electrical insulating properties and can bo used for a number of other protective purposes. are ooncerned nnd npart from the pesticide peaks " 'T roo<di-. is exact matching for nil but a few peaks in f h'niisld chroma togrn ms. . '"r. Lo- Commercial preparations of this material are usually graded according to the degreo of chlorination, but all of them nro substantially complex mixtures of polychlorobiphenyl compounds that- could be expected to resemblo The chromatograms shown wero obtained by u-"' silieono gum (GE-SE 52) column, but this precise spondeneo between tho retention times of the tho unknown compounds and those from the polph' l> coi posit "Opaqu ut 1, tho organoclilorino pesticides in their chemical nnd physical biphenyl resin has also boon demonstrated on \AplK'1'-11 kihutii.on WATER PCB-SD0000038841 ,0U 216. OCTOBER 21. 1 sk"""' 21 229 4}---- 3 11 4U - r-rrVTIOS TIRES ON THREE UltTERINI OLO COIXMKS Umc for known pesticides) (Dieldiiol-00) Aplezon 1/ Cyanoslllcone column GF-XE 60 column rcn RLE P' CB I ;t,ii i :*i js-i 3*0 2-31 2-67 3-01 6-06 5-96 6 57 2*30 2-67 305 6 06 6*05 0-56 K_LE, 1-21 1*34 2*20 2-62 2*97 360 4*63 PCB 1*21 1-33 210 2-60 2-96 3-00 4-63 kw 5-U 511 Ml extract; FCB, polychlorobiphenyl resin. . . ..ilic-om; columns. The actual retention times (or ilio peaks on these tliree types of column are . - Td.le 1. ' [J ` ....r ,.,infirmation as to tho identity of tlicso com p , .... u- been obtained by a study of their bohnviour " !uyi-r eliromat opiates, alumina and silica gol ui'columns and reverso phase pnper chromnto- , => 1:: mldition, these compoiuids have been shown Ur tbo polychlorobiphenyl compounds in their inertness. Thus thoy nre not easily modified by wi.'e i-b-inicnl reactions to produco readily identifiable >. .< m ilu ir retention times on GLC as can bo done., for to pp'-DDT by hydrolysing it to pp'-DDE or to -* ly oxidizing it to dieldrin. ' i vimU-r of livers and eggs taken from birds in tho h. I-le.-i or their coastnl waters lmvo been examined } * liibirutory with results similar to those obtained f !i<. lo-sirel liver referred to earlier. 'Whilo the idcntifica- |i u,, icompounds in British wildlife may solvo tho 1-t 11 ',vry of these peaks on GLC cliromatograms, it raises, ft ''u-r. innnv other questions. Why, for example, dp 1 \_'nilKiniuis seem to be. aeciimulalcct, most iieqnentiy ir^a-UMjiiMargest proportions, in certain types of wTid- j.' llld4i-b-aEiais^^tlTTrn hsti.^nd only at the most in Y' -''`-''"'^UTtaBoi tioiiFin man or his domestic animals sTfcli zj 1 In this respect they-seem to~di(Ter ' *rom the organocldorino pesticides which scom I! * "V" 'n'aded nearly nil nspocts of our environment and to which they bear a strong roscmbhinco chemically and physically. Some of the samples of birds examined in this laboratory have seemed to contain higher proportions of polychlorobiphcnyl compounds Ilian organocldorino pesticides. For example, the peaks on the chromatogram for tho kostrel livor shown in Fig. 1 were estimated to be equivalent to , about 12 ng of polychlorobiphenyl compounds. This must bo contrasted against tho organochlorino pesticide residues listed above. These total only about 0-8 ng of which 0-33 ng is beta-BHC, an isomer of BHC which is gcnornlly regarded os non-toxic to wildlife. Great concern has often been expressed by conservation ists about the effects of posticides on wildlife, particularly birds. Tho identification of these other organochlorine compounds in wildlife prompts enquiries as to the possible toxic effects they may be having. Xjint theso compounds nre tnvie--is--ponerally agreed13'**? tile potvchlorobiphonyls nro in fact regarded as an industrial hozardand thrcsUoTH limits lor them in nir have been advised1*. * Wo thank the Nature Conservancy for samples of wildlife and Monsanto Chemicals Ltd. for samplos of polychlorobiphenyl resins. Received Ociobcr 3, 1967. . 1 Robum, J., Analyst, 90, 467 0 985). 1 llnrrlson, R. B.. J, Sci.Food Agrir,, 17,10(1906). I Report of the Gove nnneni Chemist, 70 (ITM Stationery Office, London, 1983). ` Walker. C. H.. Hamilton, 0. A., and IlarrisoD, R. B., J. Sd. Food Agrie,, 18, 123 (1967). dc Faubort Maunder, >f. J., Euan, H-. Godly, R. W,, Hammond, E. W,, Roburn, J.. and Thomson, J., A oeitysl, 89. 16S (1964). ' Siinmom, J. H., nnd Totton, J. O'G., J, Chromatog.,27, 253 (1987). ' Abbott, D. C., E?nn, H,, and Thomson, J., J. Chromalog,, 16, 431 (1961). Evans. H., Analyst, 87. 569 (1962). Report of the Gocernrnent Chemist, 102 (nH Stationery Office, London, 1908). " Holden, A. V,t and Marsden, K., J, Proe.. fnst. Sere. Purif,, 295 (1966). II Holden, A. V., J. Jppl. Eeoli, 3, suppl., 45(1966). ' Jensen. S., Kero Set., 82, 012 (1066). "Sax, >\ Irvine. Dangerous Properties of Irvin'tried Materials, 597 (Rein hold Fubllsiilnc Corporation, Xew York, 1903). ' Brown, R. M,, Chemist-Analyst, 38. 33 (1947). 11 Documentation of Threshold Limit Values, 41 (Committee on Threshold ' Limit Values. 1966). * . _` Quasi-stellar Sources, Supernovae and Novae *f browne lnstitute f By considering the opacity of a surface layer of a star, the author concludes that quasi-stellar sources, supernovae and novae may be different manifestations of the same mechanism. '"nnlh- considored that the outbursts of novae and C; (y. 1 "'11 fundamentally different processes, but I W,ijp)i1M 1 1'!0po.w a mechanism wliich can account for 'e ptlinr"!lll'i!!!;' alld which at the snmo timo can account ';''.imi ^tl'-cms concerned, with quasi-stellar sources l;n(, ' ( 'jparticular, I suggest that theso outbursts f0r 0 anisotropic (as indeed they aro observed *:T*vnuv,'0'i\C^' ecause the energy released during a ' -igy, R0"!hurst is comparable with the stellar rest ' ^'>lcml 8?l5:ofrc'P1'c outburst could mean that tho star ^ \ rc'll*`v'st'c velocity in order to conserve vi> 1 *'"1S affording a Doppler explanation of tho O.nvijpr nts of`l>c quasi-stellar sources. 1^,4 kc opacity of a layer, L, at tho surface of a 't I. C0|l{ . * "c the thickness and R the radius of L, nnd lK<i|i,fU' Plasma at teniperatnro, T, with electron `rT,rnle ,e 10n densities N, and iNh respectively. I, will d'-ut ^ Xl., radiation of wavelength >. provided that t is to T *s l'10 op1'00! depth of L. A major conT *s T//i the optical thickness due to frcc-frcc absorptions. It is known that v^ccX'T^^jVth'i Afi (ref. 1), where induced emissions aro included. Supposo, now, that L is compressed or dilated without changing the total numbers of ions; that is, &R is vnried under conditions wliich maintain constant 4~R-ARN,, so that A/fA', = constant. Evidently t// ccNcNt AU cc A't cc 1/AI?. Thus compression of L increases its opacity, while dilation reduces the opacity. Of course, the t-otql number of ions will not remain constant in practice, because tlie recombination rate is proportional to NfNt, If the percentage of atoms ionized is large, tho density of unionized atoms, AT, will therefore be proportional to AfcAri. This means that tho contribu tion to tho opacity modo by bound-bound and boiuid-freo transitions within unionized atoms is also proportional to NCN{AR. This effect, recognized to bo important for stellar pulsation'-', further increases tho opacity of L on compression. ' ' - Somo consoquences of this variable sorfaco opacity will now bo examined. Under equilibrium conditions the n a H y- x i- -* `. T4 1 b 4 7 r.: i 4 6 s * C< J . : y \i *r - k \ i f I y1 *t - ^ *: *. i WATER PCB-SD0000038842