Retinol dehydrogenase

Retinol Dehydrogenase

Retinol dehydrogenase is an enzyme that plays a crucial role in the metabolism of retinol, also known as vitamin A. It catalyzes the conversion of retinol to retinaldehyde, which is a key step in the biosynthesis of retinoic acid, a biologically active form of vitamin A.

Structure

Retinol dehydrogenase belongs to the alcohol dehydrogenase (ADH) superfamily of enzymes. It is typically a homodimer, meaning it consists of two identical subunits. Each subunit contains a catalytic domain responsible for the enzymatic activity and a cofactor-binding domain that binds to the necessary cofactors for the reaction.

Function

The primary function of retinol dehydrogenase is to convert retinol to retinaldehyde. This reaction is essential for the synthesis of retinoic acid, which acts as a signaling molecule involved in various biological processes, including embryonic development, vision, and immune function.

Retinol dehydrogenase utilizes NAD+ (nicotinamide adenine dinucleotide) as a cofactor in the oxidation of retinol to retinaldehyde. The enzyme transfers a hydride ion from retinol to NAD+, resulting in the formation of NADH and retinaldehyde.

Role in Vision

Retinaldehyde, produced by retinol dehydrogenase, is a crucial component of the visual cycle. In the retina, it combines with the protein opsin to form rhodopsin, a light-sensitive pigment found in rod cells. When light hits rhodopsin, it undergoes a conformational change, triggering a cascade of events that ultimately leads to the generation of electrical signals, which are then transmitted to the brain for visual perception.

Clinical Significance

Mutations in the gene encoding retinol dehydrogenase can lead to various disorders related to vitamin A metabolism. For example, mutations in the RDH12 gene, which codes for a specific isoform of retinol dehydrogenase, are associated with a form of retinal dystrophy called Leber congenital amaurosis (LCA). LCA is characterized by severe vision loss or blindness in early childhood.

References

1. Belyaeva OV, Kedishvili NY. Retinol dehydrogenases. Biochim Biophys Acta. 2006;1761(7):785-796. doi:10.1016/j.bbalip.2006.04.008.

2. Haeseleer F, Palczewski K. Retinoids and the visual cycle. Annu Rev Nutr. 2010;30:399-420. doi:10.1146/annurev.nutr.012809.104807.

See Also

• Retinol
• Retinoic Acid
• Vitamin A
• Alcohol Dehydrogenase
• Rhodopsin
• Leber Congenital Amaurosis