Hormone precursors

The following acid-catalyzed cyclizations leading to steroid hormone precursors exemplify some important facts an acetylenic bond is less nucleophilic than an olelinic bond acetylenic bonds tend to form cyclopentane rather than cyclohexane derivatives, if there is a choice in proton-catalyzed olefin cyclizations the thermodynamically most stable Irons connection of cyclohexane rings is obtained selectively electroneutral nucleophilic agents such as ethylene carbonate can be used to terminate the cationic cyclization process forming stable enol derivatives which can be hydrolyzed to carbonyl compounds without this nucleophile and with trifluoroacetic acid the corresponding enol ester may be obtained (M.B. Gravestock, 1978, A,B P.E. Peterson, 1969). 

Lipids are important components of the diet fatty acids are the higher energetic source as they ensure 9kcal/g. Furthermore, some peculiar fatty acids themselves and several components of the unsaponifiable fraction are biologically active molecules, as they can act as vitamins (tocopherols— vitamin E), provitamins (carotenes—vitamin A, cholecalcipherol—vitamin D), vitamin-like (essential fatty acids), and hormones or hormone precursors (sterols—steroidal hormones). 

Sato Y., Oguchi M., Menjo N., Imai K., Saito H., Ikeda M., Isobe M. and Yamashita O. (1993) Precursor polyprotein for multiple neuropeptides secreted from the suboesophageal ganglion of the silkworm Bombyx mori characterization of the cDNA encoding the diapause hormone precursor and identification of additional peptides. Proc. Natl. Acad. Sci. USA 90, 3251-3255. 

Vitamin D regulates calcium and phosphorus absorption and deposition and serum alkaline phosphatase levels. The recommended daily allowance is 5 /xg, increasing to 10 to 15 /xg in older age.109 Vitamin D3 is synthesized under UVB irradiation in the skin where it is stored and released into the circulation in a complex with the vitamin D binding protein. In liver it is hydroxylated to 25(OH)-cholecalciferol, the hormonal precursor, followed by another hydroxylation step in the... 

Various trypsin-like serine proteases such as kallikreins [37] and plasmin or plasminogen activator [38] have been suggested to be involved in the cleavage of hormone precursors. However, it is not clearly known whether any of these proteases can correctly process proinsulin to generate both native insulin and C-peptide. Cleavage of proinsulin by plasmin is shown to result in equal amounts of insulin and a form of insulin with a residual Arg residue before the Gly at the N-terminus of the A-chain [39]. There may possibly be a novel amino peptidase for removing this... 

Androstenedione Steroid Hormone precursor Converted to estrogens and testosterone... 

Dehydroepiandrosterone Steroids Hormone precursors Converted to estrogens and... 

TABLE 28-1 Selected Hormones and Fi oqiicntly Measured Hormone Precursors and Cytoidnes—Continued... 

TABLE 28 I Selected Hormones nnd Frequently Measured Hormone Precursors and Cytokines—Condnued... 

All these indolic plant hormones or hormone precursors are likely to arise from tryptophan. Other reactions of trytophan, for example, in alkaloid l)iogenesis, are discussed in the next section. 

The generic term thyroid hormones refers to the iodinated amino acid derivatives T3 (3,3, 5-triiodo-L-thyronine) and T4 (3,3, 5,5 -tetraiodo-L-thyronine), the only iodinated hormones produced endogenously. T3 is the biologically active hormone and is, for the most part, produced from T4 in extrathyroidal tissues. T4 lacks significant bioactivity and is a hormone precursor however,... 

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