Structure and Variations
The structure of prolactin is similar to that of growth hormone and placental lactogen. The molecule is folded due to the activity of three disulfide bonds. Significant heterogeneity of the molecule has been described, thus bioassays and immunoassays can give different results due to differing glycosylation, phosphorylation, sulfation, as well as degradation. The non-glycosylated form of prolactin is the dominant form of prolactin that is secreted by the pituitary gland.
There are mainly three different forms of prolactin in regard to size:
- Little prolactin is the predominant form. It has a molecular weight of appxoximately 22-kDa. It is a single-chain polypeptide of 198 amino acids, and is apparently the result of removal of some amino acids.
- Big prolactin of approximately 48 kDa. It may be the product of interaction of several prolactin molecules. It appears to have little, if any, biological activity.
- Big big prolactin of approximately 150 kDa. It appears to have a low biological activity.
The levels of larger ones are somewhat higher during the early postpartum period.
Pit-1 is a transcription factor that binds to the prolactin gene at several sites to allow for the production of prolactin in the pituitary gland. A key regulator of prolactin production is estrogens that enhance growth of prolactin-producing cells and stimulate prolactin production directly, as well as suppressing dopamine.
Human prolactin receptors are insensitive to mouse prolactin.
Read more about this topic: Prolactin
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