Osteocalcine

Osteocalcine, more commonly known as osteocalcin, is a non-collagenous protein produced by osteoblasts in bone. It is secreted during bone formation and can become incorporated into the bone matrix or released into the circulation. The mature protein is small, consisting of about 49 amino acids, and contains three residues that undergo gamma-carboxylation, a vitamin K–dependent modification. Gamma-carboxylated osteocalcine binds strongly to hydroxyapatite in bone, while the undercarboxylated form circulates more readily in the blood.

In bone, osteocalcine is thought to participate in mineralization and calcium ion homeostasis. In addition, it has been proposed to act as a hormone that influences energy metabolism, including insulin secretion and sensitivity, adipose tissue function, and energy expenditure. Much of the evidence for hormonal roles comes from animal studies; human data are less consistent, and the exact extent of these effects remains an area of active research.

The production and carboxylation of osteocalcine are regulated by nutritional and hormonal factors, particularly vitamin K status, as well as signals from bone remodeling such as parathyroid hormone and vitamin D.

Clinically, osteocalcine serves as a biomarker of bone formation and turnover. Serum levels reflect osteoblast activity and can be measured as total osteocalcine, or in its carboxylated and undercarboxylated forms, which may provide information about vitamin K status and metabolic processes. The BGLAP gene encodes osteocalcine.