How is rubisco protected and regulated in c4 plants give reason.

Dear student,                     
​Please find below the solution to the asked query     

​Rubisco (ribulose-1-5 biphosphate carboxylase or oxygenase) is an enzyme in the calvin cycle that catalyses either the carboxylation or oxygenation of ribulose 1,5 -biphosphate with CO2 or O2. It is the most abundant protein in the world because it is present in all the plants that perform the photosynthetic activity  and molecular synthesis, by calvin cycle. 

C4 plants have special type of anatomical arrangement called as Kranz anatomy in which two types of photosynthetic cells are present in leaves. These are bundle sheath cells and mesophyll cells unlike only mesophyll cells in C3 plants. So in C4 plants Rubisco is present only in bundle sheath cells not in mesophyll cells where oxygen is released during light reactions. So oxygen is not available in bundle sheath cells for oxygenase activity of Rubisco. Only carboxylase activity of Rubisco is operated and there is no oxygenation as we see in C3 plants through photorespiration. This is how RuBisCo is regulated by C4 plants.

It is protected from hydrolysis by synthesis of CA1P (competitive inhibitor synthesised by these plants). It binds to the active site of carbamylated RuBisCO and inhibit its catalytic activity. CA1P keeps RuBisCo in such a conformaton that it is also protected from proteolysis.

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