Question

Intact mitochondrial were isolated, carefully washed with pH 7.0 buffer, and used to measure the P/O ratio for α-ketoglutarate. Included in your assay for the measurements were ADP, phosphate (Pi), NAD⁺, and malonate in an appropriate buffer. Assume that all the added compounds can get into the mitochondrial matrix and that all enzymes of the citric acid cycle are active.

Note that malonate is a competitive inhibitor or succinate dehydrogenase.

Under these conditions, what would be the P/O ratio for α-ketoglutarate?

P/O ratio = 0.5

P/O ratio = 1.5

P/O ratio = 2.0

P/O ratio = 3.5

P/O ratio = 5.0

Answer 1

The P/O ratio would be 2.0.

Because when alpha-keto glutarate will be acted by the enzyme alpha-ketoglutarate dehydrogensase one molecule of NADH will be produced this reducing power then donates it's two electrons to the electron transporter chain and by oxidative phosphorylation 2.5 ATP molecules are synthesized from ADP and Pi. Actually 2.5 molecules of ATP are produced per molecule of NADH.

Moreover when malonate is added which inhibits the succinate dehydrogensase complex only one NADH is supplied by alpha-ketoglutarate.