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larson eric elarson at ux1.cso.uiuc.edu
Wed Jul 5 15:04:56 EST 1995

Edward Doran <edoran at u.washington.edu> writes:

>	Just a quick question. How are ATP and reductant transported from the
>thylakoid membranes to the stroma?  Is it a gradient driven diffusive 
>transfer or is the process driven by active transport (and if so does a 
>gradient form anyway?).  What about the resupply of ADP? 
The synthesis of ATP occurs on the stromal surface of the thylakoids (same
for NADPH + H+).  The distances within the stroma are so small (0 to 5 um), 
and the potential concentration gradients so large (a few mM), that
diffusive transport is all that need be proposed (even considering 
tortuosity and the elevated viscosity of the stroma.)
This doesn't mean there couldn't be some sort of binding protein that
facilitated diffusion, but none has been found as far as I know (and since
one doesn't appear to be needed, it probably doesn't exist -- but never say
never in science.)

Eric Larson                  | University of Illinois at Urbana-Champaign
USDA/Agronomy                | 190 PABL; 1201 W. Gregory; Urbana, IL 61801
elarson at ux1.cso.uiuc.edu     | Voice 217.244.3079  Fax 217.244.4419
Fidonet: 1:233/4.1           | My opinions are my own, but correct :-) 

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