Adrenodoxin reductase

NADPH:adrenodoxin oxidoreductase, mitochondrial also known as adrenodoxin reductase is an enzyme that in humans is encoded by the FDXR gene, also known as ADXR. It catalyzes the following reaction:

NADPH + 2 oxidized adrenodoxin —→ 2 reduced adrenodoxin + NADP⁺ + H⁺

In both bovine and human genomes there is only a single copy of this gene.

ADXR gene is expressed in all tissues that have mitochondrial P450s. The highest levels of the enzyme is found in the adrenal cortex, granulosa cells of the ovary and leydig cells of the testis that specialize in steroid hormone synthesis. In addition the enzyme is also expressed in the liver, the kidney and the placenta.

Function

Adrenodoxin reductase is a mitochondrial flavoprotein as it carries a FAD type coenzyme. The enzyme functions as the first electron transfer protein of mitochondrial P450 systems such as P450scc. The FAD coenzyme receives two electrons from NADPH and transfers them one at a time to the electron transfer protein adrenodoxin. Adrenodoxin functions as a mobile shuttle that transfers electrons between ADXR and mitochondrial P450s.

Adrenodoxin reductase has been also called a ferredoxin-NADP+ reductase. But, determination of the sequence and structure of the enzyme revealed that it is completely different from ferredoxin reductase.