Polypeptide protein hormone

The biosynthesis of the protein hormones involves the synthesis of molecular forms larger than the polypeptide secreted from the cell [4,5]. The genetic information in DNA which codes for peptide hormones is discontinuous with intervening se-... 

Growth hormone (somatotropin GH) is a protein hormone produced in specific cells (somatotrophs) of the pituitary gland. It comprises a single polypeptide chain of about 190 amino acids which folds, with formation of two disulphide bridges, to a compact tertiary structure (see also Addendum, p. 289). Amino acid sequences have been determined for GHs from several species [1,2] and these reveal a considerable amount of species variation in particular, human GH shows extensive differences from the GHs of non-primate mammals, and this has been interpreted as indicating a rapid rate of evolution for the GH gene in the primates [3,4], Differences in biological properties between human and non-primate GHs have also been observed, and will be considered later. 

Pituitary prolactin is a protein hormone comprising a single polypeptide chain of about 200 amino acid residues and 3 intrachain disulphide bridges [1,2]. It is structurally homologous with growth hormone (GH) as is discussed in Chapter 13 (Fig. 1). Amino acid sequences of prolactins from various different species have been described [1-3] they show a considerable amount of species variation, which is most notable in the case of the prolactins of the rat and mouse, which differ from prolactins of other mammals at about 40% of all amino acid residues [3,4]. 

Figure 1.21 depicts an aitomativc pathway. Following the events of Figure 1,19, the polypeptide is inserted into the membrane, pacicaged into a secretory vesicle, and inserted into the plasma membrane via fusion of the vesicle with the PM, Membrane-bound proteins include nutrient transport proteins, hormone receptors, ion pumps, and proteins that transmit impulses along the length of a nerve or muscle fiber. 

The hormones diseassed in this chapter may be elassified. stnicturally as polypeptides, proteins, or glycoproteins These hormones include metabolites elaborated by the hypn-thalamus, pituitary gland, pancreas, gastrointestinal traci. parathyroid gland, liver, and kidney.s. A comprehensive review of the biochemistry of these polypeptides and iitber related hormones is beyond the scope of this chapter. Fora detailed discu.s.sion. the reader should refer to the review by Wallis el al. and other literature cited ihroughnui thu chapter. 

Adrenocorticotropic hormone (ACTH), insulin, and parathyroid hormone (PTH) are examples of polypeptide or protein hormones. They are generally water soluble and circulate freely in plasma as the whole molecule or as active or inactive fragments. The half-life of these hormones in plasma is quite short (10 to 30 minutes or less), and wide... 

MlO. Morgan, C. R., A two antibody system for radioimmunoassay of protein hormones. In Protein and Polypeptide Hormones, Proc. Int. Symp. (M. Margoulies, ed.). Part 1, pp. 49-54. Excerpta Med. Found., Amsterdam, 1968. 

The regulation of metabolism is in part due to polypeptide and protein hormones, the products of the endocrine system. With the development of recombinant DNA techniques, specific protein hormones can now be made using bacteria and yeast. There has been ongoing discussion and controversy concerning the genetic manipulation of proteins for medical and commercial purposes. 

Animal hormones essentially fall into four different chemical classes (1) amine-derived hormones, (2) peptide/protein hormones, (3) steroid hormones, and (4) lipid or phospholipid hormones. Amine-derived hormones such as catecholamines and thyroxine are derivatives of the amino acids tyrosine and tryptophan. Peptide hormones including insulin, growth hormone, and vasopressin consist of polypeptides ranging in length from 5 to 200 residues. Steroid hormones such as estrogen... 

Another important peptide hormone is adrenocorticotropic hormone (ACTH). It is synthesized by the pituitary gland and consists of a single polypeptide chain of 39 amino acid residues with no disulfide bridges (see I Figure 9.3). The major function of ACTH is to regulate the production of steroid hormones in the cortex of the adrenal gland. > Table 9.2 lists these and some other important peptide or protein hormones. 

---