Carbonic Anhydrase 4/CA4 (CA4) Active Protein

Carbonic anhydrases (CAs) are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. They participate in a variety of biological processes, including respiration, calcification, acid-base balance, bone resorption, and the formation of aqueous humor, cerebrospinal fluid, saliva, and gastric acid. They show extensive diversity in tissue distribution and in their subcellular localization. This gene encodes a glycosylphosphatidyl-inositol-anchored membrane isozyme expressed on the luminal surfaces of pulmonary (and certain other) capillaries and proximal renal tubules. Its exact function is not known; however, it may have a role in inherited renal abnormalities of bicarbonate transport. [provided by RefSeq, Jul 2008]

CA4: Reversible hydration of carbon dioxide. May stimulate the sodium/bicarbonate transporter activity of SLC4A4 that acts in pH homeostasis. It is essential for acid overload removal from the retina and retina epithelium, and acid release in the choriocapillaris in the choroid. Defects in CA4 are the cause of retinitis pigmentosa type 17 (RP17). RP leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well. RP17 inheritance is autosomal dominant. Defective acid overload removal from retina and retinal epithelium, due to mutant CA4, is responsible for photoreceptor degeneration, indicating that impaired pH homeostasis is the most likely cause underlying the RP17 phenotype. Belongs to the alpha-carbonic anhydrase family.

Protein type: Energy Metabolism - nitrogen; Lyase; Membrane protein, GPI anchor; EC 4.2.1.1

Chromosomal Location of Human Ortholog: 17q23

Cellular Component: Golgi apparatus; cell surface; rough endoplasmic reticulum; sarcoplasmic reticulum; brush border membrane; basolateral plasma membrane; secretory granule membrane; ER-Golgi intermediate compartment; trans-Golgi network; anchored to external side of plasma membrane; membrane; perinuclear region of cytoplasm; apical plasma membrane; plasma membrane; sarcolemma

Molecular Function: protein binding; carbonate dehydratase activity; zinc ion binding

Biological Process: response to drug; response to steroid hormone stimulus; bicarbonate transport; organ development; one-carbon compound metabolic process

Disease: Retinitis Pigmentosa 17