NAD(P)H-hydrate epimerase is an enzyme that in humans is encoded by the NAXE gene (previously APOA1BP).
Mutations in NAXE gene are associated with progressive encephalopathy with brain edema and/or leukoencephalopathy-1 (PEBEL-1), a rare, lethal, neurometabolic disorder.

Structure
NAXE gene is located on chromosome 1, with its specific location being 1q22. The gene contains 6 exons, 5 introns, and spans 2.5 kb. Expression is ubiquitous across all human tissues, with highest observed in kidney, heart, liver, testis, thyroid gland, adrenal gland. NAXE contains Yje_FN domain.

Function
NAXE binds to APOA1, APOA2, and high-density lipoprotein (HDL). In addition, APOA1BP appears to play a role in sperm capacitation. It has been demonstrated that APOA1BP is involved in angiogenesis regulation, by accelerating cholesterol efflux from endothelial cells to HDL. It is known that zebrafish NAXE ortholog Aibp is involved in angiogenesis regulation. The protein was also shown to be involved in atherosclerosis protection.

Enzyme class

More generally, an NAD(P)H-hydrate epimerase (EC 5.1.99.6, NAD(P)HX epimerase) is a type of enzyme with systematic name (6R)-6beta-hydroxy-1,4,5,6-tetrahydronicotinamide-adenine dinucleotide 6-epimerase. Enzymes of this class, especially NAXE and its orthologs, catalyse the following chemical reaction

(1) (6R)-6beta-hydroxy-1,4,5,6-tetrahydronicotinamide-adenine dinucleotide



⇌


{\displaystyle \rightleftharpoons }

(6S)-6beta-hydroxy-1,4,5,6-tetrahydronicotinamide-adenine dinucleotide
(2) (6R)-6beta-hydroxy-1,4,5,6-tetrahydronicotinamide-adenine dinucleotide phosphate



⇌


{\displaystyle \rightleftharpoons }

(6S)-6beta-hydroxy-1,4,5,6-tetrahydronicotinamide-adenine dinucleotide phosphate
The enzyme can use either (R)-NADH-hydrate or (R)-NADPH-hydrate as a substrate.

References

External links
NAD(P)H-hydrate+epimerase at the U.S. National Library of Medicine Medical Subject Headings (MeSH)