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Re: Q: phosphoinositides: translocases?



>> Subject: Q: phosphoinositides:  translocases?
>> Reply-to: wolfgang.schechinger@med.uni-tuebingen.de
>> Sender: owner-kinases@postal.sdsc.edu
>> Precedence: bulk
>> Status: U
>>
>>Hi all,
>>
>>I've noticed that a higher phosphorylated phosphoinositide (PI4,5P2)
>>is to some extent in the outer membrane of erythrocytes, while its
>>precursor PI-4P is not.
>>Is there evidence for a translocase now or new ideas how any why
>>PIP2 gets into the outer membrane since a spontaneous flipflop is
>>unlikely due to the highly negative charge of the molecule and the
>>size of the head group?
>>
>>Are there new ideas?
>>
>>Wolfgang
>
>Wolfgang,
>
>Do treatments/conditions that result in appearance of PS in the outer
>leaflet of the membrane increase the amount of PIP2?
>
>Cheers,
>
>Jim
>-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>James E. Ferrell, Jr., M.D., Ph.D.

Dear Wolfgang:

An outward flip of PIP2 could be the result of activation of a non-specific
flippase, such as the Ca2+-activated scramblase (see recent papers by Sims
et al.).  However, a couple of groups have evidence that, in the presence
of Ca2+, PIP2 can induce lipid reorientation (see Schiffer et al.,
Biochemistry 37 (1998) 3449 (and references therein) and work by Sulpice et
al.).  As far as I know, no one has reported evidence for an outwardly
directed PIP2-specific translocase.

Regards,

David

P.S. Jim - how've you been?

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David Daleke
Department of Biochemistry & Molecular Biology    (812) 855-6902
Indiana University School of Medicine         fax (812) 855-4436
Medical Sciences, Jordan Hall 108            daleked@indiana.edu
Bloomington, Indiana 47405        http://php.indiana.edu/~dldlab
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