1,25-dihydroxyvitamin D(3) 24-hydroxylase, mitochondrial; A cytochrome P450 monooxygenase with a key role in vitamin D catabolism and calcium homeostasis. Via C24-oxidation pathway, catalyzes the inactivation of both the vitamin D precursor calcidiol (25-hydroxyvitamin D(3)) and the active hormone calcitriol (1-alpha,25- dihydroxyvitamin D(3)). With initial hydroxylation at C-24 (via C24- oxidation pathway), performs a sequential 6-step oxidation of calcitriol leading to the formation of the biliary metabolite calcitroic acid. Hydroxylates at C-24 or C-25 other vitamin D active metabol [...]

Retinoic acid receptor RXR-alpha; Receptor for retinoic acid that acts as a transcription factor. Forms homo- or heterodimers with retinoic acid receptors (RARs) and binds to target response elements in response to their ligands, all-trans or 9- cis retinoic acid, to regulate gene expression in various biological processes. The RAR/RXR heterodimers bind to the retinoic acid response elements (RARE) composed of tandem 5'-AGGTCA-3' sites known as DR1-DR5 to regulate transcription. The high affinity ligand for retinoid X receptors (RXRs) is 9-cis retinoic acid. In the absence of ligand, t [...]

Parathyroid hormone; PTH elevates calcium level by dissolving the salts in bone and preventing their renal excretion; Belongs to the parathyroid hormone family.

Fibroblast growth factor 23; Regulator of phosphate homeostasis (By similarity). Inhibits renal tubular phosphate transport by reducing SLC34A1 levels (By similarity). Acts directly on the parathyroid to decrease PTH secretion (By similarity). Regulator of vitamin-D metabolism (By similarity). Negatively regulates osteoblasts differentiation and matrix mineralization (By similarity). Upregulates EGR1 expression in the presence of KL; Belongs to the heparin-binding growth factors family.

Vitamin D-binding protein; Involved in vitamin D transport and storage, scavenging of extracellular G-actin, enhancement of the chemotactic activity of C5 alpha for neutrophils in inflammation and macrophage activation.

Sodium-dependent phosphate transport protein 2A; Involved in actively transporting phosphate into cells via Na(+) cotransport in the renal brush border membrane. Probably mediates 70-80% of the apical influx.

Vitamin D3 receptor; Nuclear receptor for calcitriol, the active form of vitamin D3 which mediates the action of this vitamin on cells (By similarity). Enters the nucleus upon vitamin D3 binding where it forms heterodimers with the retinoid X receptor/RXR (By similarity). The VDR-RXR heterodimers bind to specific response elements on DNA and activate the transcription of vitamin D3-responsive target genes (By similarity). Plays a central role in calcium homeostasis (By similarity).

Sodium-dependent phosphate transport protein 2C; May be involved in actively transporting phosphate into cells via Na(+) cotransport in the renal brush border membrane. Probably mediates 20-30% of the apical influx; Belongs to the SLC34A transporter family.

Klotho peptide; May have weak glycosidase activity towards glucuronylated steroids. However, it lacks essential active site Glu residues at positions 241 and 874, suggesting it may be inactive as a glycosidase in vivo. May be involved in the regulation of calcium and phosphorus homeostasis by inhibiting the synthesis of active vitamin D. Essential factor for the specific interaction between FGF23 and FGFR1; Belongs to the glycosyl hydrolase 1 family. Klotho subfamily.