Osteocalcin, also known as bone gamma-carboxyglutamic acid-containing protein (BGLAP), is a noncollagenous protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 found in bone and dentin. In humans, the osteocalcin is encoded by the BGLAP gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.

Function

Osteocalcin is secreted solely by osteoblasts and thought to play a role in the body's metabolic regulation and is pro-osteoblastic, or bone-building, by nature. It is also implicated in bone mineralization and calcium ion homeostasis.
Osteocalcin acts as a hormone

Hormone

A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

 in the body, causing beta cells in the pancreas

Pancreas

The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...

 to release more insulin

Insulin

Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

, and at the same time directing fat cells to release the hormone adiponectin

Adiponectin

Adiponectin is a protein which in humans is encoded by the ADIPOQ gene.- Structure :...

, which increases sensitivity to insulin.

Current data suggests a possible role of osteocalcin in male fertility. Research from Columbia University Medical Center proposes that osteocalcin may enhance the synthesis of testosterone, which is a hormone believed to regulate aspects of male fertility. Although these studies were originally performed by one laboratory (Dr. Gerard Karsenty), at least two other groups have independently confirmed the role of osteocalcin in insulin secretion.

Use as a biochemical marker for bone formation

As osteocalcin is produced by osteoblasts, it is often used as a marker for the bone formation process. It has been observed that higher serum-osteocalcin levels are relatively well correlated with increases in bone mineral density (BMD) during treatment with anabolic bone formation drugs for osteoporosis, such as Forteo

Teriparatide

Teriparatide is a recombinant form of parathyroid hormone, used in the treatment of some forms of osteoporosis. It is manufactured and marketed by Eli Lilly and Company.-Administration:...

. In many studies, osteocalcin is used as a preliminary biomarker on the effectiveness of a given drug on bone formation.