A research team led by the University of Bonn, and also involves
researchers from Argentina, Canadaand the University of D??sseldorf
provides new insights into an enzyme that plays a key role in C4
photosynthesis.

Around three percent of all plants have developed a trick that enables
them to use even the smallest amounts of CO2 in C4 photosynthesis. In
this process, they first pre-fix CO2 by linking it to a transport
molecule, producing an organic compound containing four carbons - hence
the name C4 photosynthesis. This is transported into the bundle sheath
cells, which are specially sealed. Here, the carbon dioxide is released
again and is then available for further reactions of photosynthesis.
This release step is catalyzed by the NAD-malate enzyme (C4-NAD-ME).

For a long time, it was unclear exactly how C4-NAD-ME functions. The
research team investigated this using an ornamental plant of the genus
Cleome. The team found that NAD-ME consists of two large building
blocks, the alpha and the beta subunit. While the alpha unit is
responsible for CO2 release, the beta subunit serves primarily to
regulate the activity of the enzyme.

This regulation is extremely important because CO2 release takes place
in the mitochondria, where important metabolic processes are constantly
taking place. The beta subunit apparently prevents the two enzymes from
getting in each other's way, regulating the reaction rate of C4-NAD-ME.
To do this, it binds an intermediate product of the C4 photosynthesis
cycle called aspartate. Aspartate ensures that the "photosynthetic
variant" of NAD-ME becomes particularly active. The CO2 that is
pre-fixed and intended for photosynthesis is thus mainly processed by
the enzyme variant that "matches" it (and works much faster).

Key mechanism of photosynthesis elucidated â?? University of Bonn
(uni-bonn.de)
[www.uni-bonn.de]