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Here is a question I have been wanting to bring up.  Is a reaction with
triplet oxygen the only way to quench an XFP?  I know that for the excited
state to cross over to a state where it can fluoresce, it must release
energy as heat.  Can it release enough heat to denature itself and possibly
proteins around it?  I know with FRAP many of the photobleachings tend to
use a ton of laser power to ensure complete bleaching.  This seems like it
could lead to problems with thermal denaturation.  It could also lead to a
discrepancy in results if one person pours a lot more laser power into their
bleach area than another person does.

-----Original Message-----
From: Confocal Microscopy List [mailto:[log in to unmask]]On
Behalf Of Guy Cox
Sent: Friday, October 10, 2003 1:07 AM
To: [log in to unmask]
Subject: Re: FRAP


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I'm not suggesting that depleting oxygen will be sufficient to
prevent reactive oxygen species forming IF something is forming
them.  What I'm questioning is whether a FRAP bleach of (eg)
FITC will create any reactive oxygen species.  I can't see why
it would.  Bleaching is probably just the reaction of fluorescein
with normal molecular oxygen, via the mechanism I gave.

                                                Guy



>>>While I agree with Jim in principle on this one, I would make a
>>>coupl of comments.
>>>
>>>1. Bleaching is most often a result of electron being excited into
>>>a triplet state which will then react very easily with oxygen (which is
>>>naturally in a triplet state) since triplet-triplet reactions are
>>>favoured.  Hence bleaching will deplete oxygen not the opposite.
>>>Antifades (= photographic developers) are mild reducing agents which
>>>scavenge oxygen to prevent bleaching.
>
>I would qualify the above statement. Depleting oxygen in the manner
>described is insufficient to prevent radical cascade as alluded to in
>my previous posting. As a rule, the only way to kill a radical is
>with another radical. Some antifades work by either forming a poorly
>reactive radical species, or as in the case of cysteine, self
>terminates by combining with itself to form cystine. In a membrane,
>once you've got a carbon centered radical, hope for the nearest
>Vitamin E.
>--
>_________________________________________________________________
>Mario M. Moronne, Ph.D.
>NanoMed Technologies LLC
>President and CTO
>ph (510) 528-2400
>FAX (510) 528-8076
>1561 Posen Ave
>Berkeley, CA
>94706
>
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