20:
263:
In photosystem II, pheophytin plays a very similar role. It again acts as the first electron carrier intermediate in the photosystem. After P680 becomes excited to P680, it transfers an electron to pheophytin, which converts the molecule into a negatively charged radical. Two negatively charged
143:
and plastoquinone (Klimov, Allakhverdiev, Klevanik, Shuvalov). This discovery was met with fierce opposition, since many believed pheophytin to only be a byproduct of chlorophyll degradation. Therefore, more experiments ensued to prove that pheophytin is indeed the primary electron acceptor of
275:
molecule and leaves photosystem II. The reactions outlined above in the section concerning purple bacteria give a general illustration of the actual movement of the electrons through pheophytin and the photosystem. The overall scheme is:
166:
Pheophytin is the first electron carrier intermediate in the photoreaction center (RC P870) of purple bacteria. Its involvement in this system can be broken down into 5 basic steps. The first step is excitation of the
195:
passing an electron to pheophytin, producing a negatively charged radical (the pheophytin) and a positively charged radical (the special pair of chlorophylls), which results in a charge separation.
402:
Xiong, Ling, and
Richard Sayre. "The Identification of Potential Pheophytin Binding Sites in the Photosystem II Reaction Center of Chlamydomondas by Site-Directed Mutagenesis." (2000).
692:
392:
590:
717:
337:
Klimov VV (2003). "Discovery of pheophytin function in the photosynthetic energy conversion as the primary electron acceptor of
Photosystem II".
856:
264:
pheophytin radicals quickly pass their extra electrons to two consecutive plastoquinone molecules. Eventually, the electrons pass through the
545:
74:. In both PS II and RC P870, light drives electrons from the reaction center through pheophytin, which then passes the electrons to a
921:
82:) in RC P870 and RC P680. The overall mechanisms, roles, and purposes of the pheophytin molecules in the two transport chains are
478:
131:
In 1977, scientists
Klevanik, Klimov, Shuvalov performed a series of experiments to demonstrate that it is pheophytin and not
144:
PSII, occurring between P680 and plastoquinone (Klimov, Allakhverdiev, Shuvalov). The data that was obtained is as follows:
154:
Photo-reduction of pheophytin occurs at temperatures as low as 100K, and is observed after the reduction of plastoquinone.
450:. CollinsDictionary.com. Collins English Dictionary - Complete & Unabridged 11th Edition. Retrieved October 19, 2012.
251:
The fifth and final step involves the filling of the “hole” in the special pair by an electron from a heme in cytochrome
958:
139:(EPR), they were able to show that pheophytin was reducible and, therefore, the primary electron acceptor between
136:
255:. This regenerates the substrates and completes the cycle, allowing for subsequent reactions to take place.
471:
148:
Photo-reduction of pheophytin has been observed in various mixtures containing PSII reaction centers.
135:
that serves as the primary electron acceptor in photosystem II. Using several experiments, including
55:
963:
786:
464:
158:
These observations are all characteristic of photo-conversions of reaction center components.
885:
864:
792:
447:
782:
772:
496:
168:
99:
molecule lacking a central Mg ion. It can be produced from chlorophyll by treatment with a
151:
The quantity of pheophytin is in direct proportion to the number of PSII reaction centers.
8:
778:
733:
707:
898:
768:
362:
697:
625:
575:
354:
47:
423:
366:
911:
820:
814:
764:
557:
346:
51:
175:
or the special pair of chlorophylls. This can be seen in the following reaction.
877:
635:
580:
520:
314:
211:
The third step is the rapid electron movement to the tightly bound menaquinone, Q
71:
67:
810:
654:
630:
435:
324:
299:
215:, which immediately donates the electrons to a second, loosely bound quinone (Q
59:
350:
952:
929:
838:
832:
756:
725:
585:
132:
28:
850:
530:
488:
358:
828:
525:
456:
309:
304:
96:
438:
Definition of pheo in The
American Heritage Stedman's Medical Dictionary
702:
608:
567:
515:
265:
645:
617:
510:
104:
100:
906:
535:
802:
75:
19:
684:
678:
672:
666:
382:
63:
662:
426:
Merriam-Webster
Medical Dictionary definition of Pheophytin
319:
140:
103:, producing a dark bluish waxy pigment. The probable
373:
424:http://dictionary.reference.com/browse/pheophytin
950:
378:(4th ed.). Redondo Beach, CA: Plycon Press.
258:
16:Chlorophyll molecules lacking a central Mg2+ ion
161:
755:
472:
436:http://dictionary.reference.com/browse/pheo-
486:
479:
465:
383:Nelson, David L.; Cox, Michael M. (2005).
336:
387:(4th ed.). New York: W. H. Freeman.
126:
18:
951:
95:In biochemical terms, pheophytin is a
460:
376:Illustrated Guide to Food Preparation
385:Lehninger Principles of Biochemistry
219:). Two electron transfers convert Q
404:America Society of Plant Biologists
397:Library of 3-D Molecular Structures
13:
191:The second step involves the (Chl)
107:comes from this description, with
14:
975:
393:Photosynthetic Molecules Section.
66:, and the type II photosynthetic
410:
137:electron paramagnetic resonance
441:
429:
417:
1:
374:McWilliams, Margaret (1982).
330:
259:Involvement in photosystem II
207:+ ·Pheo (charge separation)
90:
7:
293:
162:Reaction in purple bacteria
10:
980:
289:Regeneration of substrates
920:
897:
876:
801:
746:
716:
653:
644:
616:
607:
566:
553:
544:
506:
495:
56:electron transfer pathway
50:that serves as the first
693:Magnesium protoporphyrin
959:Photosynthetic pigments
351:10.1023/A:1024990408747
286:Plastoquinone reduction
223:to its reduced form (Q
35:
793:Protoporphyrinogen IX
127:History and discovery
22:
886:Bacteriochlorophyll
865:Bacteriochlorophyll
169:bacteriochlorophylls
54:intermediate in the
899:Isobacteriochlorins
734:Protochlorophyllide
708:Zinc protoporphyrin
247:(quinone reduction)
70:(RC P870) found in
34:without the Mg ion.
779:Coproporphyrinogen
183:+ 1 photon → (Chl)
36:
946:
945:
942:
941:
938:
937:
742:
741:
698:Protoporphyrin IX
626:Adenosylcobalamin
603:
602:
599:
598:
576:Phycoerythrobilin
283:Charge separation
48:chemical compound
971:
912:Sirohydrochlorin
878:Bacteriochlorins
765:Uroporphyrinogen
753:
752:
651:
650:
614:
613:
558:Phytochromobilin
551:
550:
504:
503:
481:
474:
467:
458:
457:
451:
445:
439:
433:
427:
421:
388:
379:
370:
52:electron carrier
979:
978:
974:
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972:
970:
969:
968:
949:
948:
947:
934:
916:
893:
872:
797:
748:
738:
718:Phytoporphyrins
712:
655:Protoporphyrins
640:
636:Methylcobalamin
595:
591:Phycoviolobilin
581:Phycocyanobilin
562:
540:
521:Stercobilinogen
499:
491:
485:
455:
454:
446:
442:
434:
430:
422:
418:
413:
406:. 22 Apr. 2007.
399:. 22 April 2007
345:(1–3): 247–53.
339:Photosynth. Res
333:
315:Reaction center
296:
272:
261:
246:
242:
238:
235:2·Pheo + 2H + Q
230:
226:
222:
218:
214:
206:
203:+ Pheo → ·(Chl)
202:
194:
186:
182:
174:
164:
129:
93:
81:
72:purple bacteria
68:reaction center
17:
12:
11:
5:
977:
967:
966:
961:
944:
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940:
939:
936:
935:
933:
932:
926:
924:
918:
917:
915:
914:
909:
903:
901:
895:
894:
892:
891:
882:
880:
874:
873:
871:
870:
862:
844:
826:
811:Chlorophyllide
807:
805:
799:
798:
796:
795:
790:
776:
761:
759:
757:Porphyrinogens
750:
744:
743:
740:
739:
737:
736:
731:
722:
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714:
713:
711:
710:
705:
700:
695:
690:
659:
657:
648:
642:
641:
639:
638:
633:
631:Cyanocobalamin
628:
622:
620:
611:
605:
604:
601:
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593:
588:
583:
578:
572:
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563:
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541:
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483:
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440:
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415:
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412:
409:
408:
407:
400:
389:
380:
371:
332:
329:
328:
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325:Chlorophyllide
322:
317:
312:
307:
302:
300:Photosynthesis
295:
292:
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270:
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192:
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172:
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156:
155:
152:
149:
128:
125:
92:
89:
88:
87:
86:to each other.
79:
60:Photosystem II
15:
9:
6:
4:
3:
2:
976:
965:
964:Tetrapyrroles
962:
960:
957:
956:
954:
931:
930:Cofactor F430
928:
927:
925:
923:
919:
913:
910:
908:
905:
904:
902:
900:
896:
890:
889:
884:
883:
881:
879:
875:
869:
868:
863:
860:
859:
854:
853:
848:
845:
842:
841:
836:
835:
830:
827:
824:
823:
818:
817:
812:
809:
808:
806:
804:
800:
794:
791:
788:
784:
780:
777:
774:
770:
766:
763:
762:
760:
758:
754:
751:
745:
735:
732:
730:
729:
724:
723:
721:
719:
715:
709:
706:
704:
701:
699:
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691:
688:
687:
682:
681:
676:
675:
670:
669:
664:
661:
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652:
649:
647:
643:
637:
634:
632:
629:
627:
624:
623:
621:
619:
615:
612:
610:
606:
592:
589:
587:
586:Phycourobilin
584:
582:
579:
577:
574:
573:
571:
569:
565:
559:
556:
555:
552:
549:
547:
543:
537:
534:
532:
529:
527:
524:
522:
519:
517:
514:
512:
509:
508:
505:
502:
498:
494:
490:
489:tetrapyrroles
482:
477:
475:
470:
468:
463:
462:
459:
449:
444:
437:
432:
425:
420:
416:
405:
401:
398:
394:
390:
386:
381:
377:
372:
368:
364:
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356:
352:
348:
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340:
335:
334:
326:
323:
321:
318:
316:
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308:
306:
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301:
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297:
288:
285:
282:
279:
278:
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274:
267:
256:
254:
234:
233:
232:
198:
197:
196:
178:
177:
176:
170:
159:
153:
150:
147:
146:
145:
142:
138:
134:
133:plastoquinone
124:
122:
118:
114:
110:
106:
102:
98:
85:
77:
73:
69:
65:
61:
57:
53:
49:
45:
41:
38:
37:
33:
32:
26:
21:
887:
866:
857:
851:
846:
839:
833:
821:
815:
727:
726:Chlorophyll
685:
679:
673:
667:
531:Urobilinogen
443:
431:
419:
403:
396:
384:
375:
342:
338:
268:
262:
252:
250:
210:
190:
187:(excitation)
165:
157:
130:
120:
116:
112:
108:
94:
83:
43:
39:
30:
29:chlorophyll
24:
829:Chlorophyll
568:Phycobilins
546:Phytobilins
526:Stercobilin
310:Chlorophyll
305:Photosystem
239:→ 2Pheo + Q
97:chlorophyll
62:(PS II) in
44:phaeophytin
23:Pheophytin
953:Categories
847:Pheophytin
749:porphyrins
703:Pterobilin
646:Porphyrins
618:Corrinoids
609:Macrocycle
516:Biliverdin
411:References
331:References
280:Excitation
266:cytochrome
121:vegetation
40:Pheophytin
511:Bilirubin
487:Types of
105:etymology
101:weak acid
91:Structure
84:analogous
922:Corphins
907:Siroheme
803:Chlorins
536:Urobilin
500:(Linear)
367:29278470
359:16228584
294:See also
119:meaning
111:meaning
747:Reduced
497:Bilanes
76:quinone
27:, i.e.
365:
357:
64:plants
363:S2CID
199:(Chl)
179:(Chl)
171:(Chl)
113:dusky
46:is a
663:Heme
448:phyt
355:PMID
320:P680
141:P680
117:phyt
115:and
109:pheo
787:III
773:III
347:doi
231:).
58:of
42:or
955::
855:,
837:,
819:,
785:,
771:,
683:,
677:,
671:,
395:"
361:.
353:.
343:76
341:.
123:.
78:(Q
888:a
867:c
861:)
858:b
852:a
849:(
843:)
840:b
834:a
831:(
825:)
822:b
816:a
813:(
789:)
783:I
781:(
775:)
769:I
767:(
728:c
689:)
686:o
680:a
674:c
668:b
665:(
480:e
473:t
466:v
391:"
369:.
349::
273:f
271:6
269:b
253:c
245:2
243:H
241:B
237:B
229:2
227:H
225:B
221:B
217:B
213:A
205:2
201:2
193:2
185:2
181:2
173:2
80:A
31:a
25:a
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