Second Assignment

My Favorite Hormone Structure

Figure 1: Multiple amino acid Sequence Alignment of Inhibin in Rainbow trout (BAB19272), Zebra fish (NP 571143), Rhesus monkey(NP 001028127), Norway rat(NP 036722), and house mouse(NP 034694) . Alignments were made using ClustalW software. Legend : ":" conserved substitutions , "*" residues are identical in all sequences of the allignment, "." semi-conserved substitutions.

Inhibin is a heterodimeric glycoprotein that is found in the seminal plasma and follicular fluid. It is secreted from the granulosa cells of the ovary in females, and from the Sertoli cells of the testes in males, to control secretion of Follicle Stimulating Hormone. Inhibin is produced in the placenta, gonads, pituitary gland and other organs (Wikipedia, 2007). The secondary structure of inhibin consists of one alpha chain that is ~18 kDa and one beta chain that is ~14kDa, these two subunits are linked by disulfide bridges. Each subunit ( alpha and beta) is produced from a seperate gene and is produced as a large precurser protein. There are two separate beta-subunit genes, and thus two distinct proteins (beta-A subunit and the beta-B subunit). Therefore there are two "kinds" of inhibin, inhibin-A or inhibin-B, and each may exist in 7 to 9 different molecular forms. Due to the many combinations there are a number of different dimeric inhibin forms(Hopko JL et al.,1994). Inhibin in its "mature" form has a molecular weight of 32,000 daltons (Ying, 1988).
Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) contain identical alpha subunits of 92 amino acids, however there beta chains vary, FSH has 118 and LH has 121 amino acids. All three hormones (FSH, LH and Inhibin) are involved in ovulation.
The known receptors of Inhibin are poorly understood when compared to its structurally similiar molecule activin. Inhibin is known as an activin antagonist and operates by competing for activin receptors rather then having its own receptors. However , inhibin is also known to bind with great affinity and specificity with membrane-binding proteins that could possibly be the supposed inhibin receptor. (Robertson et al.,2000)




References

Hopko Ireland JL, Good TE, Knight PG & Ireland JJ 1994 Alterations in amounts of different forms of inhibin during follicular atresia. Biology of Reproduction 50 1265-1276.

Inhibin. (2007, February 22). In Wikipedia, The Free Encyclopedia. Retrieved 17:29, February 25, 2007, from http://en.wikipedia.org/w/index.php?title=Inhibin&oldid=109986814
Robertson, DM., Herton R. & Farnworth PG. (2000). Is the action of inhibin mediated via a unique receptor? Reproduction. The Journal of the Society for Reproduction and Fertility. 5, 131-135. Society of Reproduction and Fertility. Retrieved February 25th 2007 from http://ror.reproduction-online.org/cgi/content/abstract/5/3/131

Ying, SY. (1988). Inhibins, activins, and follistatins: gonadal proteins modulating the secretion of follicle-stimulating hormone. Endocrine Reviews 9 267-293. Retrieved February 25th 2007 from www.medvet.umontreal.ca/crra_ang/CAP_inhibine.pdf