Document MGykqLr6XMODZwZ7pXXMGkZOy

NATUUC. VOL. 2 16. OCTC : 2 1. 1967 chain is (crmmalnl and the completed cliain released from (lie ribosome-wRN A coni|ile\- to which it is bound by the (KNA molecule carrying tbc la-sl amino-acid incorporated. There must be a mechanism for reading the ehnin terminating codon (three codons UAA, UAG, and UGA can code for chain termination) and cleaving the last pept idyl-/RXA bond. In JSiochem. Iliophys. lies. Comm., 28, 773 (1907) he describes an experimental system devised to give n rapid assay for chain termina tion, and in Pyoc. US Nul. Acad. Sci., 58, 1144 (1907) he reports the discovery of an enzyme required for terminal inn. The assay for termination employs the UNA from nn amber mutant of the coat protein gene of the RNA bacteriophage 1117. This mutant has an amber codon, UAG, at the position of the. sixth amino-acid, a gluta mine residue, in the A'17 coal protein molecule. In a cell free system the nminni, UNA direcLs the synthesis of a small N-terminul peptide of the coat protein with the sequence X-formylmot.-ala-sor-nspn-phc-thr; tho next amino-acid in the coat protein is glutamine, blit, with tho mutant. UNA the amber codon causes pre mature termination of synthesis and the release of the hcxnpcptido. Tho great, virtue of this system is that the imterminat.cd peptide still attached to the pept idyl* (UNA can be distinguished from the terminated peptide released from the (UNA and the amounts of each measured. Furt hermore, starving the system for any one of the six amino-acids in the peptide arrests the trans lation 'machinery beforo it reaches tho UAG codon so termination can be controlled. Exploiting this proccduro, Capccchi isolated a compiox of ribosome, mRNA and pentapeptide attached by t he. phenylalunyl fUXA simply by starvin'' for threonine. With this ho 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 rclensc it is necessary but not sufficient to complete the peptide, by incorporating threonino and that release is not solely dependent on the transfer enzymes required to move the ribosome from tbc threonyl codon to tho UAG terminating codon. Release does, however, depend upon the presence of a supernatant factor. This factor, with a molecular weight of between 40,000 and 50,000, sediments between 3-5N and 4-55'. Because its releasing activity is not affected by RXasc, it cannot be an UNA-protcin 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 tho /UNA from peptidy!-/U.\'A already released into the supernatant, which was tho other possibility. ' Capc.cchi does not yet know whether the release cnzyinc works atone or in conjunction with ot her factors, in particular a hypothetical chain termination (UNA which reads the termination codon but docs not carry an amino-acid. Many people, including Capccchi, linve searched in vain for such a /UNA species, and although negative results can nover exclude the possibility that such (UNA exists it is reasonable to think about alternative models in which tho terminating codons arc read cithc-r by the ribosome or tire release enzyme or in which nonsenso codons function simply because they cannot bo read at ail. Further characterization of the release enzyme could well decide tiro issuo. Chlorinated Hydrocarbons in British Wildlife by D. C. HOLMES , J. H. SIMMONS J. O'G. TATTON Laboratory o( the Government Ctemist, London Poiychlorobiphenyl compounds have been detected In British wildlife. In birds' livers and eggs they are often in greater quantities than organochlorine pesticide residues. Polychlorobiphenyls are known to be toxic, and their detection In wildlife raises the question of the adverse effect they may have. Wiius wild birds' eggs or tho livers of British wildlife nru examined lay gas-liquid chromatography (GI.C) using rlreirou-eupturo dotoetioii, peaks corresponding to such "rgauueldorino pestieidos us BiJC, die.hirin and DDT, and (heir metabolites and breakdown products, often npponr mi llie resultant chromatograms. Those penks sumot.imcs represent amounts which uro significant from a toxicolo gical point of view, but t.ho sensitivity of modern instru ments nlso enables completely insignificant amounts to be delected. Analysts concerned with tho determination of organochlorine pesticides in wildlife, howovor, lmvo long been awaro thill, it is not unusual for nn additional series of as many ns ton ponies, corresponding t.o unidentified compounds, also to nppoar on those chromatograms1'*. Little is known of tho structure and origin of thoso com pounds, but Roburn' oslnblishod that they aro organo- chlorine in nature, with a substantial chlorine content, and consequently possess electron-cnpluring properties. On silicono or 'Apioznii' OI,C columns, the series of peaks for I heso compounds normally begins nt tho point at which pp'-TDE and jip'-DDT are emerging from the columns and extends, in terms of retention times, to four or fivo times that of pp'-I)I)T, which is tho last of tho commonly occurring pesticides to emerge. Boforo examination by OI-C, snmples have normally boon subjected to a fairly rigorous clean-up procedure, such as t hat- of do Faubort Maunder el all, which includes a dimothylformnmido-hoxnno partition and passage through a column of prepared alumina. Because these unknown compounds aro similar in nature and properties to tho orgnnoehlorino posticidos, thoy also pass thruugh this and similar elonn-up procedures; consequently, they DSW 027919 STLCOPCB4011881 27.0 NATURE, VOL. 216. OCTOBER 21. 19G7 often interfere Borioualy with determination* of j-'p'-TDK and p/J-DDX in wildlife bocnuso of overlapping of the chromatographic peaks. Suitaldo procedures lmvo been devised to overcome this diflioulty of interfering ponies. One method i* to effect a bolter resolution of theso particular peaks by ehoieo of u suitable stationary phapo for OLC*. Another method, which also dcmonMrales the pjosenco of t)u*so compound* in tho snmplo, is tho uso of n picliminary thin-layer chromatographic i t rout mould, Tho cleaned-up ex i ract-s nro examined on silica go! e)n nmalupln! es using n 1 jht rent buiulion of ueelono in beNane as mobile phase*. Spots corresponding to tho compound? can then bo found at A> values between 0-8 and 1-0, whereas tho com* monly oceun ing orgonoc-hlorino pesticides and their metabolites produce spots of lower J'p values, A similar Reparation can also be shown with rovorso phase paper ehromnto graphy* whereby tho unknown compounds move only n very short distance from tho ha so lino compared with tho pesticides and their metnhohtes. Cuts-liquid chromatography using dual channel detection systems with separate electron-capture end fln mo* ion t station del.ee* tor* 1ms also been used to demonstrate tho presence of largo amounts of weakly elect ron- eapturing inatorin), in nddilion to known pesticide residues, in tho eggs of oyster entellers (IJnetnntvpus oslrulcrfua)*, Kxporioneo in this laboratory lias shown that, these compounds occur most frequently and in the largest proportions in tho livers, fat arid eggs of birds, particularly terrestrial predators such ns spnrrowlmwk? {Afripiicr nr.vt/j) and kestrels (1'ulco linnuuculus) and marine feeders such as guillemots (Vria ttnhjc) and kitti wakes [Ktssn (ridnchfla)] they also commonly occur in freshwater fl*b. Wo have detected small amounts in human and animal fat samples, but less Jrequcntly nnd in much smaller proportions Kkx 1. GftP-Slquld chronmlorrnm of (a) r-stmcl of kr^trcl liver nnd (ft) n. commercial polyrMorubiphcrn 1 rest n. than in avian samples. A similar series of chromatographic peaks lias boon properties. In tho prescribed extraction nnd GT.C condi observed by Holden1'*1 when examining extracts of soalg tion?, these mixtures produce a series of chromatographic and fish taken in Scottish waters. }lo found that tho pcak9 penks of tho typo in question. given by tho extracts of flesh nnd ten-water fish represen Tho compounds occurring in British wildlife correspond ted fairly low concentration*, but those given by extracts to tho more highly chlorinated biphenyl compounds rather of seal blubber corresponded to much Imger proportions, than the more lightly chlorinated types. These highly of the order found by tins laboratory in birds' eggs. chlorinated biphenyls also occur to semo extent in tho ] )cspito conskhwablo curiosity about the identity of those analogous polyeldoroteiphenyl preparations which lm\e compounds, littlo progress ha* boon jnndo in identifying commercial uses similar to those of polychlorobiphenyl. them, but Micro 1ms long been a general supposition Mint It. is possible Mint some of tbo compounds with very loop (hoy weic oil her further breakdown or condensation retention times occurring in British wildlife nro lightly product9 of tho nrgnnochlorino pesticides or possibly chlorinated polychloi old phenyl compounds, looxo compound* of theso with natural products Hiieh ru Big. hr shows tho gus-liquid chromatogram of an pro! ein matt er. extract, from a kestrel liver. The peaks corre-pondin" to Jenson, however, KUOCreded in identifying n Furies of (0 IB ng). beta-BIK' ng) and ganuna-BMC such peaks as corresponding to pelychlnrolnphenyl com (P-O'l ng) are labelled. 'I'lie other peaks* J'nrin tho series pounds, in 2U0 piko taken ill diflnrent- parts of Sweden, referred to nltdvi' nnd nut H now \\ on Id ] ia \ e been i rga i d-d and in mi eagle11, ^Nr<> lmvo now h<M`ii able to show llmt pimply ns "unknown OT'g.morhhiriuo compounds net tho long retention time compounds occunhig in British eo-.TC'-pOMding te any known pe-ilicide ev ifs met ubel i t <". wildlife are also pnlyehlni ohiphenyl compounds. Big. )b shows tlu' analogous clirttnin! ogi mn of a coauirr- J'ulvehlurinated biphenyl has bean in common commer cifd polyeldfa-oliiplif*iyl resin. So far ns retention Mine? cial use for some t ime as a plast ici/.or in paints, resins find are rnneerni'd and apart- from the pe-diehlc peaks, Micro plasties. Jt- also 1ms electrical 'insulating properties nnd is exiiet- matching for all but. a few peaks in the two can bo used fur ti numb- r of other piotcctivo purposes. elireTiudegruins. ('omm'-reiu] prepnr at ions of this mat-mini are usually The chi omul ogmms shown were obt ained 1,\* use ('f a gjiid'-d aeeniding to l-ho d'g'CO of ehloriuaf ion, but all of silicone gum {CJ'S-SF* U'l) column, but this nitci^n enrretlani nrn sub1-1 ant ially comph-x mixtures of polychlmo- sprmdenee hotN',e,,n tin* ?ti ei*1 irn limes of i he penh-far hiplmnyl eojiipaunds that could la* esjirrlud t ii,';',mblo tic unleravn n'lnnmnd'! arid th"'0 liem th tli" nrganochloi ira- post i rides in t heir ela-mienl and pliydeal hiphenyl resin 1 ms a !?.o 1 ren <i,uon,-M v<\ I *-d on .-e. i ,<> "V-eii // OSW 027920 fi ATL'c .|*Uo sn:cv>. KLK \-v: ]-7i MU 5 i. * 31 M71 ' f''3 MO KM'-. > l cy ord/, von it bmr y/UiaU . thi* e"':nr J*u yf tTlL-<. I if roe r' vi -npla f u dLs ii j, -tano drin 1 A m-. j' i if ish this r Iho .a i o f ",*V lev al in Mle ry sii Cow.Mt-loa; ha Qu P- F l, ' 've''sit S- '=n,:c j f ' IS \lv fj f ' m i > , ` 1 l,, a pi- r- >ti, l.l -IM H;, I"' f. >1`! I r:: \ . i-'-i-.-! L, STLCOPCB4011882 21. \OC/J * i < c'iniicrdtl NATURE. VOL. 21 0, O JLR 21. 1907 20 r | ' 1 1 i ' , V 1 *1 V ' j | J 'j " v / ' / * I1 TjiMo 1. Ju;i.A'iivk ju;n;.vn(N timi.n on tiiju.k Mm.i.i.xr olo columns (JTiliiJin;; tiiiu i [or know n piu-ticMlrh) Silicons G)l' si; i,`* raluiun Kt.K I'CU (ni. lilr.n - 100) /on J/ column kj,v: l'CIt Vy.ii M'S.Hi (.no OK- XI. GO column j\ irn ) 12 1-12 ]:; : T.i i-ei i-ia :m 231 2 i.7 :i-u4 r.-nu *j::o J-C.7 ,V0f, 1 21 l L' i j-'a :i-71 :e;o 4 r-s i r.s :.G2 !, r.-.` 7 10 7 11 i.-tMl 01-7 O.iG 2'!`7 r.n J -CU i. ) i J.' J.K, Krt-trcl liver oxlr:icl; 1*0 U, polychlnrobijiNrnyl roum. 1-21 K::i mi a MOO M-aG :i co 403 ill cl i id oynnn-dlioone columns. The i* cl i m t re I out ion time* recorded for tho peaks on l-luvo three typos of column nro (jivnn ill Till lo 1. Kurlher confirmation ns to tho identify c>f the^o com pounds ]inh boon oblnined by n study of their behaviour on thin-lnyor ehvomnloplates, nlunmin and silica g.-l absorption columns and rovorso phase paper chromato grams. In addition, those compounds h:ivo lx-on Miown to rosomblo t-ho polvohlorobiphcnyl compounds in (heir chomic.nl iivrlnoss. Thus they aro not easily modified by simple chemical reactions to produoo readily ident-ifiablo shifts in their retention times on GKC ns can be done, for instance, to p;/-].)DT by hydrolysing it to p/Z-DDlC or to aldrin by oxidizing it to dioldriri. A number of livers ami eggs taken from birds in the llrituh Isles or their coastal waters havo been oxamined in this laboratory with results similar to tl)OJ*o obtained for t bo best rol liver referred (o earlier. While the idontifioalion of those compounds in Dritish wildlife may solve tho mystery of those peaks on GKO chromatograms, it raises, however, many other questions. Why, for example, do those compounds seem to be accumulated, most frequently and in tho largest proportions, in certain typos of wild life sue)) ns birds seals and iiwh, and only at t-ho most- in very small proport ions in man or Ids domestic animals such ne cowr or sheep? In this respect they seem to differ markedly from tho organochlnrino pesticides wliidi scorn to havo invaded nearly all aspects of our onviremment and U> which they hour n Mroiig' rcsf-MiUmicf. clicmioj.il>- iu,il plivuioiilly. iSojno nf (ho miiii[i1os oTliirfis oxiiinifir .1 iii (iiis hr.horM ory linvo Buoiui-d lo contain higher jiroport ioim cCjk-iIvcl.Ifrn`ii\T compounds than Org.'mochlririim pr-stipid.-R. For example, tho pc.aks on tho chromatogram f>r (lie kestrel liver shown in big. \ were estimated to bo equivalent to about 12 ng of polyohlorotaphonyl compounds. This must be coo! nisied against thn organochlnrino pesticide residues h.-Ud above. These total only about 0'8 ng of which f> G3 ng is bota-KlIC. na isomer of JUIC which in generally regarded us uou-toxio to wildlife. Groat, concern hns often been expressed by conservnlioniftr. about- tho (iffccls of pofiticuleR on wildlife, particularly birds. Tho ident ifioat ion of thoso ot 1 <:r orgunodiloriiio compounds in wildlife prompts enquiries ns to the possible toxic effects they may bo hnvmg. That thoso compounds nro toxic is generally ngrocciu>u; tho polyeb'orobi* phenyls are in fact regarded as an industrial hazard and threshold limits for them in nir havo boon ndvhcd14. ^ o thank tho NTt-uro Conservancy for samples of wildlife nnd Monsanto Chemicals Ktd. for tampion of polyoldorobiphcnyl resinfc. Pmivert Octobr'r 3. KG7. 1 lU.l.nrii, J., Analyst, 00, JO? O0CG). * lUrrihon, K. Jl., J. Sri. Pool Ayrir.,V. 10Onr,6), * )irpr-rl <f Government Chrtni*t, 70 (11M St *(ioii"ry O/Tirp, l.n rulofi. 1 003). I W.ilkcr. 0. 11.. M.inuMon, G. A., ami H*irn*on, It. IK, J. Sci. Food Agric., 13. 12:1 <KH;7J. * Jr V:ti!nrl Mruimlrr. M. J., Kf'in. It., Ooilly, 17, W., IlnrrnnonT K. W,t llolairii, ,1., anJ 'J'linmMon, .1., Anaty,t, 59. 1G^ (1001), * Simmons, J. It., anti Tati on, J. O'G., J. Chro'nnUii.. 27, 2G3 (1007). * AM'Oll, I>. C., J'.s.'tn. It. aul ThnmMm, J., J. CArinrvx/^ff., 16,161(1901). * KViU.p, It., Annb.nt, 87. f.GO (19G2). * 7,V;if-r( of ihr Govcrtwirnl CVicmil/, 102 (IIM St-ttlonrry 0IV`ce. Lotnlon, Mif.G). l' Jlolilen, A. V., and Mar<!cn, K., J. rror. Imt, Sr\r. Puri/., 2Oj (100G). n IW.lilf-n, A . V., ,7. Ajiji! F.rnl., 3, Biiptl., 4f (J OOfl). II Jciifrn, S., -Yop Sri., 22. G12 (10GG). " Snx. N. Irvin**, J)an$rr<itu Pro}>frlir' nf Industrial ZfaJrriali, 507 (Krin- Itold I'ul.IiHhtni: (;or|Kr.ition, New York, 1DG3). 54 llrown, U. M., Chrmixt-A tinJysl, 30, 83 (KM7). 11 poruuirnlolion of Threshold f.imil Valurt, 41 (CoaimlLU-o on Threshold l.iuiil Vnlmn. K>CG). .1 G KG l-ondi* .inuUeginjihic fv con expend aounds nit her 'J'iirset }uglily \11 11f in Out i which have thiitil u] i] icnyl. . it li very long Te are lighOv .gram r*f an l r -j mndit ig t O g.imm/t-l11 0 ii i u t-1 irt scries b'-en jcganhul :ii]M'Unds not metabolite*) . of a oojumcrtmtion times < pr.ikj*, tbero :s in the two A f I | j f i l J ' J J ( j * l (1 by nso (>f a pt ectMi corro- kiUs for ycbloro- n `Ajue/.on />' [ j 1 Quasl-stellar Sources, Supernovae and Novae by ' P. F. BROWNE University o( Manchester Institute of Science and Technology By considering the opacity of a surface layer of a star, the author concludes that quasl-stellar sources, supernovae and novae may be different manifestations of the same mechanism. It is usually considered that the oulb\ir>ts of novno nnd Mipemovno nro fundamentally different processes, but- I shall hero propose n mechanism which can account for both phenomena, and which at tho sumo lime can account for ether problems concerned witli qunsi-slollar sum cos (qunsnrs). In particular, I suggest that thoso outbursts nro likely to be anisotropic (as indeed they nro observed to bo for novae). Kecnuso Ibo energy released during a supernova outburst is comparable with tho stellar rest energy, an anisotropic outburst could moan that the star i ne.celoralod to relativistic velocity in order lo conserve moment inn. thus nffonling a Doppler explanation of tho hirgu rod-shiffs of i,ho quasi-stellar sources. Consider the opacity of a layer, L, nt the surface of a st ar. hot A fl lo t-1 ic thickness and /.* t lie radius of T., and let L contain plasma nt temperature, T. with electron nnd positive ion densities -Y, and -Y( rcspecUN'ely. Is will bo opaque to radiation of wavelength \ jn'ovided that *: nhout I, win re t is tho oplieal depth of Is. A major con tribution to t is 7//, the optical thickness duo to froo-froo absorptions. It is known that %>'T~> ny ,Ni A II (ref. 1). where induced emissions nro included. Suppose, now, that Is is compressed or dilated without changing the mini numbi'is of ions; that is, A Tt is varied iinilcr conditions; which maintain constant *1 rr/i^A/KY,, so that AKA,-- constant. Kvidently 7// cc AK-Y( A/' a: JV( cc 1 / AII. Thus compression of Is increases its opacity, uhile dilation retlurtes tho opacity. Of course, tho total number of ions vill not icnmin 0(nslant- in praet-iee, becanso tho recombinnl ion >a!e is juoportional (o If (ho pcncentago of atoms i*n!yrd is liu ge, (lie d(msity of nnicni/.ed ntoms. Y, will t her. fa o bn projxirtioiifd to fVhis inoniis that the contribu tion to tho opacity nindo hy bound-houtid and bound-free Irnusih'r.us willun unioiii/.ed atoms is also propoitifmal to AT.Y,A 11. This ofiect, recognized to bo impirfnnf fur sti llar pulsation1'*, furtlier increases tho opne-iiy of L on coiujircssien. Some consequences of this variable surface opacity vill now bo examined. Under equilibrium combtiona (ho DSW 027921 STLCOPCB4011883