Structures of most nuclear histones are well conserved within and between species. Inactive genes tend to be highly methylated. Protein synthesized along the ribosome is transferred into and through the endoplasmic reticulum and Golgi complex. Protein hormones are packaged into secretory granules within the Golgi apparatus. Residual hormone is stored in granules and thereby made readily available for secretion upon a subsequent bout of cellular stimulation.
Peptide bonds linking amino acids are susceptible to enzymatic attack.
Terminal residues of sialic acid on glycosylated proteins are removed by plasma glycosidases. Hepatic cells recognize the exposed asialo hormone. Vertebrate GnRHs are composed of 10 amino acids. An extrahypothalamic version of GnRH, with sequence homology to chicken GnRH II, has been reported in marsupials. Gonadotropin-releasing hormone is cleaved from a prohormone during posttranslational processing.