Phosphoenol Pyruvate Carboxylase

(Orthophosphate: Oxaloacetate Carboxylase Phosphorylative EC 4.1.1.31)

This enzyme is involved in the fixation of carbon-dioxide in C₄ plants. It has a high affinity to CO₂ molecule. The reaction catalyzed by this enzyme is given below.

Phosphoenol Pyruvate + CO₂	PEP Case	Oxaloacetic acid

Sorghum, maize, sugarcane etc. are some of C₄ plants.

Principle

The oxaloacetic acid formed by the action of PEP case is coupled with MDH and followed by NADH oxidation. Since the sources of PEP case contain enough MDH there is no need to add MDH exogenously.

Materials

» Tris HCl Buffer 0.1M (pH 7.8)
» Magnesium Chloride (10mM) 203.5mg/50mL water.
» Sodium Bicarbonate (10mM) 84mg/100mL water
» Phosphoenolpyruvate (5mM) 23.28mg/100mL water
» NADH (0.4mM) 5.32mg/10mL water
» Enzyme extract - see under MDH

Procedure

1. Mix various recipes as shown below:

Sr. No.	Reagents	Test (mL)	Blank (mL)
1	Tris-HCl buffer pH 7.8	0.8	1.3
2	Magnesium chloride	0.5	0.5
3	Sodium bicarbonate	0.5	0.5
4	Phosphoenol pyruvate	0.5	0.5
5	Enzyme extract	0.2	0.2
6	NADH	0.5	0

2. Proceed steps 2 to 4 as in MDH
.

Calculation

Calculate as for MDH.

References

1. Ting I P and Osmond, C B (1973) Plant Physiol 51 439.
2. Sadasivam, S and Gowri, G (1981) Photosynthetica 15 453.

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