jhsh at maties.sun.ac.za (Jannie Hofmeyr) wrote:
(...)
>The only plant-specific PPi-dependent reaction they refer to is an
>alternate route catalysed by FP-PTase
>>fructose-6-P + PPi ---> fructose-1,6-bisP + Pi
>>Here it seems that there are two parallel ATP and PPi-using enzymes.
>However, the PPi one is thought to work principally in the reverse
>direction to supply PPi for sucrose breakdown via UDP-glucose
>pyrophosphorylase. FP-PTase has been found only in higher plants, some
>algae, ryophytes and Rhodospirillum.
Higher plants normally have both an ATP dependent and a PPi dependent
phosphofructokinase. The expression of both enzymes depends largely on
developmental state etc. The thing on the PPi dependent PFK is that it is
activated by fructose-2,6-bisphosphate, that also inhibits
fructose-1,6-biphosphatase. This double action allows for a regulation of the
direction of glycolysis or gluconeogenesis. This is important in plants as they
have to adapt between carbohydrate storage and using depending on day or night,
the kind of organ, growth or reserve/seed formation etc.
These relations should be rather fascinating for some MCA work. Isn't anyone out
there doing it?
Albrecht
