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تسجيل

Chemistry of the Anterior Pituitary Hormones: Growth Hormone

المؤلف:  Norman, A. W., & Henry, H. L.

المصدر:  Hormones

الجزء والصفحة:  3rd edition , p67

2026-06-25

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As shown in Figure 1 the gene for human growth hormone (hGH) contains five exons and four introns. GH gene expression in somatotrophs requires the transcription factor Pit-1, which is also involved in the control of the expression of hormone-encoding genes in lactotrophs and thyrotrophs. The majority of circulating GH is derived from the complete set of five exons and is a protein of 191 amino acids with a molecular weight of 22 kD. Approximately 10–15% of circulating GH is smaller (176 amino acids, 20 kD) due to the omission of 15 amino acids encoded in the first section of exon III. The ratio of the two forms of growth hormone in the blood is relatively constant and is independent of age.

Fig1. Gene and amino acid sequences of growth hormone (GH). The two main forms of GH are shown. GH- 22k (left), is derived from all five exons whereas in GH- 20k use of an alternative splice site in exon III results in omission of 15 amino acids, which are indicated in pink in GH-22k.

Human placental lactogen (hPL, also known as chorionic somatomammotropin, hCS) is produced by the placenta and is very closely related to hGH. Its gene lies in the same cluster on chromosome 17; hPL also contains 191 amino acids, shares greater than 90% amino acid identity with hGH and probably arose from a new duplication of the primate GH gene or extensive interchange of the GH gene with the PL genes. hPL circulates primarily in the maternal compartment and has little direct effect on fetal growth. Further discussion of the GH gene cluster and the functions of hPL can be found in Chapter 14.