25-Hydroxyvitamin D 1-alpha-hydroxylase

Enzyme involved in vitamin D metabolism

25-Hydroxyvitamin D 1-alpha-hydroxylase is an enzyme that plays a crucial role in the metabolism of vitamin D. It is responsible for the conversion of 25-hydroxyvitamin D (calcidiol) into 1,25-dihydroxyvitamin D (calcitriol), the active form of vitamin D in the body.

Function

25-Hydroxyvitamin D 1-alpha-hydroxylase is primarily found in the kidneys, where it catalyzes the hydroxylation of calcidiol at the 1-alpha position. This reaction is a key step in the activation of vitamin D, which is essential for maintaining calcium and phosphorus homeostasis in the body. The enzyme is regulated by several factors, including parathyroid hormone (PTH), calcium levels, and phosphate levels.

Regulation

The activity of 25-hydroxyvitamin D 1-alpha-hydroxylase is tightly regulated by the body's needs for calcium and phosphate. When calcium levels are low, PTH is secreted by the parathyroid glands, which stimulates the enzyme to produce more calcitriol. Calcitriol then acts to increase calcium absorption from the intestine, reabsorption from the kidneys, and mobilization from bone. Conversely, high levels of calcium and phosphate inhibit the enzyme's activity.

Clinical significance

Deficiency or dysfunction of 25-hydroxyvitamin D 1-alpha-hydroxylase can lead to disorders such as rickets in children and osteomalacia in adults, due to impaired production of calcitriol. Genetic mutations affecting the enzyme can result in conditions like vitamin D-dependent rickets type 1 (VDDR1), also known as pseudovitamin D deficiency rickets.

Related enzymes

25-Hydroxyvitamin D 1-alpha-hydroxylase is part of the cytochrome P450 family of enzymes, specifically the CYP27B1 gene. Other related enzymes include 25-hydroxyvitamin D 24-hydroxylase, which is involved in the catabolism of vitamin D metabolites.

Related pages

• Vitamin D
• Calcidiol
• Calcitriol
• Parathyroid hormone
• Calcium metabolism

Gallery

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  Calcidiol
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  Calcitriol