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calbindin 1, 28kDa
Identifiers
Symbol	CALB1 CALB
HUGO	1434
Entrez	793
OMIM	114050
RefSeq	NM_004929
UniProt	P05937
Other data
Locus	Chr. 8 p11

calbindin 2, 29kDa (calretinin)
Identifiers
Symbol	CALB2
HUGO	1435
Entrez	794
OMIM	114051
RefSeq	NM_001740
UniProt	P22676
Other data
Locus	Chr. 16 q22.1

Calbindin describes calcium binding proteins first described as the vitamin D-dependent calcium binding proteins in intestine and kidney.

Calbindin-D9k is present in mammalian intestinal epithelial cells (enterocytes) and mediates the transport of calcium across the enterocytes from the apical side, where entry is regulated by the calcium channel TRPV6, to the basolateral side, where calcium pumps such as PMCA1 utilize intracellular adenosine triphosphate to pump calcium into the blood. Calbindin-D9k can also be found in the kidney and uterus in some mammalian species.

The transport of calcium across the enterocyte cytoplasm appears to be rate-limiting for calcium absorption in the intestine; the presence of calbindin increases the amount of calcium crossing the cell without raising the free concentration. Calbindin-D9k may also stimulate the basolateral calcium-pumping ATPases. Expression of calbindin-D9k and calbindin-D28k are both stimulated by the active vitamin D metabolite, calcitriol although the precise mechanisms are still controversial. In mice in which the receptor for vitamin D is not expressed, calbindin-D9k is reduced, but not absent.

Calbindin-D28k performs a similar role in the intestine in birds and in the mammalian kidney; it is also found in a number of other neuroendocrine cells, particularly in the cerebellum. There is no homology between calbindin-D28k and calbindin-D9k, except Apart from their calcium binding domains (EF-hands): calbindin-D9k has two EF-hands, and calbindin-D8k has six.

Calbindin is pronounced as "cal bind in" with a "i" sound as in "bind". It is also pronounced as "cal bin din" with an "i" sound as in "bin". Given the derivation of the name from calcium binding, the former is technically correct.

• Vitamin D-dependent calcium-binding protein