Subject: Re: Structurally modified chlorophylls in reaction centre(s)?
From: [email-masked] (Jonathan B. Marder)
Date: Tue, 7 Jun 1994 06:05:13 GMT
Newsgroups: bionet.photosynthesis

In article <[email-masked]> [email-masked] (Philip Bacon) writes:
>Subject: Structurally modified chlorophylls in reaction centre(s)?
>From: [email-masked] (Philip Bacon)
>Date: Sun, 5 Jun 1994 21:01:58 +0000

>Could chemically- or enzymically-modified chlorophylls be
>present and have a role in photosynthetic reaction centre(s)?
>-------------------------------------------------------------

>I have not been active in chloroplast work for some 25 years
...
>The question then arises -- does recent work UNAMBIGUOUSLY preclude the
>possibility of e.g. a 13¬2 -OH being present in one or more of the reaction
>centre chlorophylls?

You have missed some developments in 25 years!  First there was Senger's
suggestion that the P700 donor of PSI may be chlorinated.  The same group
subsequently showed this to be an interesting artifact.  There are now
suggestions that P700 may be a pair of 13¬2 epimers (chl a') - you could
follow the work of T. Watanabe on this (apologies to anyone else also working
on this).  It seems that PSI may be the only complex which contains chl
a' in vivo.  There seems to be a similar story with Heliobacterium where the
reaction center P798 seems to contain bchl g' rather than bchl g which forms
the bulk.  The suggestion is that dimerization of the epimers in the reation
centres gives more red-shift than you would get with normal chl a or bchl g.

Regarding others RC's,  it seems pretty well established (by biochemical
means) that the purple bacterial have only bchl a (e.g. R. shaeroides) or
bchl b (e.g. R. viridis - the Michel/Deisenhofer organism) in the reaction
centres.

The PSII reaction centre has been shown to have all its chlorophyll
exclusively  as chl a.

I hope that this helps.  Anyone have references on hand?
__
Jonathan B. Marder                 '
Department of Agricultural Botany  |     Internet: [email-masked]
The Hebrew University of Jerusalem | /\/ Bitnet:   MARDER@HUJIAGRI
Faculty of Agriculture             |/  \ Phone:    (08 or +9728) 481918
P.O.Box 12, Rehovot 76100, ISRAEL  /     Fax:      (08 or +9728) 467763