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Re: CO2 and enzyme stuff
>
>Date: Tue, 27 Jan 98 15:46:58 cst
>From: mark.fisher at tpwd_state.tx.us
>Subject: Re: CO2 use at nightime?
>
> CO2 is used directly by plants; there is no chemical precursor or
> storage product for CO2........
> The enzyme responsible for carboxylating ribulose 1,5-bisphosphate is
> named, appropriately enough, ribulose bisphosphate carboxylase, or
> rubisco, for short........
> Mark
>Date: Tue, 27 Jan 1998 19:01:02 -0800 (PST)
>From: Eric Scheeff <edscheef at sdcc14_ucsd.edu>
>Subject: Re: CO2 use at nightime?
>
>This is probably true in all aquatics but not all plants. Many desert
>plants employ a system in which CO2 is taken up by the plant at night and
>temporarily fixed into a storage molecule (not ribulose..................I
don't remember the >detailed biochemistry but I think these plants are
called CAM plants.
>Water not being a major concern for aquatic plants <g> I don't think that
>this comes into play in our systems, and so I apologise for straying into
>the "Off Topic Zone". Just wanted to set the biological record straight.
>- -Eric
>
The enzyme is phosphoenol pyruvate carboxylase (PEPcarboxylase or PEPc'ase)
and the substrate is carbonate. It functions in many CO2 concentrating
mechanisms including CAM and C4. Assimilation of inorganic carbon (CO2)
into sugars in these mechanisms is still accomplished via Rubisco as Mark
points out. I would not guess either CAM or C4 mechanisms would function in
aquatic environments but another CO2 concentrating mechanism that does
function in aquatics are carbonate pumps. In some algae, such as _Chara_
(stonewort), carbonate is actively pumped inside the organism from the
surrounding outside water. I am not aware of a carbonate pump in higher
aquatics but would be very interested if anyone knew of an example.
Dennis J. Harney
Miami University Botany Dept.
In snowless Oxford, OH where merchants are still trying to unload sleds and
shovels.