CHAPTER 24 – Evolution of Protein Molecules

Flavonoids are nearly ubiquitous in plants and are recognized as the pigments responsible for the colors of leaves, especially in autumn. They are rich in seeds, citrus fruits, olive oil, tea, and red wine. They are low molecular weight compounds composed of a three-ring structure with various substitutions. This basic structure is shared by tocopherols (vitamin E). Flavonoids can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. These characteristics appear to also be required for best activity, especially antioxidant and antiproliferative, in the systems studied. The particular hydroxylation pattern of the B ring of the flavonoles increases their activities, especially in inhibition of mast cell secretion. Certain plants and spices containing flavonoids have been used for thousands of years in traditional Eastern medicine. In spite of the voluminous literature available, however, Western medicine has not yet used flavonoids therapeutically, even though their safety record is exceptional. Suggestions are made where such possibilities may be worth pursuing.

The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer

Enkephalin, a natural ligand for opiate receptors is composed of the pentapepides H-Tyr-Gly-Gly-Phe-Met-OH and H-Tyr-Gly-Gly-Phe-Leu-OH. The evidence is based on the determination of the amino acid sequence of natural enkephalin by the dansyl-Edman procedure and by mass spectrometry followed by synthesis and comparison of the natural and synthetic peptides.

Identification of two related pentapeptides from the brain with potent opiate agonist activity

The last two decades have been an era of rapid progress in peptide research. This era was begun by the work of Sanger on the amino acid sequence determination of insulin and by du Vigneaud on the structure determination and synthesis of oxytocin. This period has seen impressive progress in the structure elucidation and synthesis of many peptides of natural origin and of great biological significance, as well as in methods for sequence determination and chemical synthesis of peptides [1–4]. Perfection of techniques and instruments for automatic determination of the amino acid sequence of peptides and proteins has made possible a greatly broadened understanding of genetics and evolution as well as the more chemical areas of mechanism of action of enzymes and hormones, and physical chemistry of peptides and proteins. Effective methods of peptide synthesis are crucial to progress in this area, because only by synthesis can adequate amounts of important peptides be made available for chemical, biologi...

Solid Phase Peptide Synthesis

Proteins of moderate size having native peptide backbones are produced by a method of native chemical ligation. Native chemical ligation employs a chemoselective reaction of two unprotected peptide segments to produce a transient thioester-linked intermediate. The transient thioester-linked intermediate then spontaneously undergoes a rearrangement to provide the full length ligation product having a native peptide bond at the ligation site. Full length ligation products are chemically identical to proteins produced by cell free synthesis. Full length ligation products may be refolded and/or oxidized, as allowed, to form native disulfide-containing protein molecules. The technique of native chemical ligation is employable for chemically synthesizing full length proteins.

https://science.sciencemag.org/content/sci/266/5186/776.full.pdf

Synthesis of proteins by native chemical ligation

The isolation of an untriakontapeptide from camel pituitary extracts has been described. Its structure has been determined and shown to be identical to the sequence of carboxyl-terminal 31 amino acids of ovine beta-lipotropin. The peptide possesses very low lipotropic activity but significant opiate activity.

https://www.pnas.org/content/pnas/73/4/1145.full.pdf

Isolation and structure of an untriakontapeptide with opiate activity from camel pituitary glands

beta-Endorphin, an opiate-like peptide, has potent antinociceptive properties when it is administered directly into the brain and assayed in the the tail-flick, hot-plate, and writhing tests in mice and in the wet shake test in rats. On a molar basis, beta-endorphin is 18 to 33 times more potent than morphine and its actions are blocked by the specific opiate antagonist, naloxone hydrochloride. The activity of beta-endorphin in vivo is also compared to other peptides that show opiate-like activity in assays in vitro.

https://www.pnas.org/content/pnas/73/8/2895.full.pdf

beta-endorphin is a potent analgesic agent.

Hormonal Proteins and Peptides

introduction It has been known for some time that pituitary growth extracts stimulate the bony epiphyses of rats and that the increments in the width of the epiphyseal cartilage of hypophysectomized rats as results of growth hormone injections is proportional to the dosage (Li and Evans, 1948). This led Evans et al. (1943) to propose a simple bioassay method for estimating growth hormone potency. It was found that the method is highly sensitive and simple as compared to other techniques. In this paper we attempt to standardize the procedure and apply it to the assay of pure and crystalline growth hormone. preliminary experiments Prior to the standardization of the test procedure, certain experiments were done varying the route of administration, the duration of the test period, and the frequency of injections of hormone. In these experiments, both tibiae were removed 24 hours after the last injection, fixed in acetone, and stained immediately with silver nitrate, as described below.

Bioassay of hypophyseal growth hormone: the tibia test

AN untriakontapeptide1 with significant opiate activity from camel pituitary glands was shown to have an amino acid sequence identical to the carboxyl-terminal 31 amino acids of β-lipotropins2,3. The peptide, designated as β-endorphin, has recently been synthesised4, and when administered directly into the brain, it was found5 to be considerably more potent than morphine in molar basis, and its actions were blocked by naloxone. Other peptides related to β-lipotropins have also been shown to possess in vitro opiate-like activity6–9. We report here the analgesic effects of β-endorphin when it is injected intravenously.

Choh Hao Li

Papers

Isolation and structure of an untriakontapeptide with opiate activity from camel pituitary glands

beta-endorphin is a potent analgesic agent.

Hormonal Proteins and Peptides

Bioassay of hypophyseal growth hormone: the tibia test

Beta-Endorphin as a potent analgesic by intravenous injection.