Proline protein synthesis

Some members of the Liliaceae accumulate free azetidine-2-carboxylic acid in a much higher concentration than that found to be lethal to mung bean seedlings, but it is not incorporated into their proteins. Fowden (43) postulated that these plants either had a proline-incorporating system which was more specific than that found in other species, or some subcellular mechanism operated to prevent the homolog from reaching the sites involved in protein synthesis. Data which supported the first suggestion were subsequently obtained (116). 

The hydroxyl group is added to proline after synthesis into protein and is only found in collagen and gelatine — has two asymmetric carbon atoms... 

The successful use of [ F]FDG in oncology PET imaging has prompted the design of several other radiopharmaceuticals, such as [ F]FLT ([ F]fluorothymi-dine, used as cellular proliferation marker. Scheme 36) [152-154], F-MISO ([ F] fluoromisonidazole, used to assess tissue hypoxia. Scheme 37) [155], c/s-4-[ F] fluoro-L-proline (used as abnormal collagen synthesis marker. Scheme 38) [156] and 0-(2-[ F]fluoroethyl)-L-tyrosine (used as amino acid transport and/or protein synthesis marker. Scheme 39) [157]. All these fluorine-18-labelled molecules have been prepared by aliphatic nucleophilic fluorination followed by a deprotection reaction. 

K. Hamacher, Synthesis of n.c.a. cis- and trans-4-[ F]fluoro-L-proline, radiotracers for PET-investigation of disordered matrix protein synthesis, J. Label. Compds Radiopharm. 42 (1999) 1135-1144. 

However, little is currently known about its synthesis. The protein component may be assembled on the ribosomes by the normal mechanism of protein synthesis.324 L-Proline is known to be the precursor of the hydroxy-L-proline found in the glycoprotein,324,325 hydroxylation of the peptide-bound L-proline being catalyzed, in carrot cells, by cytoplasmic enzymes.324... 

Nutritional Effects Due to the Presence of the Maillard Products. Many physiological or antinutritional effects have been attributed to the Maillard products. Specific effects have been attributed to the Amadori products deoxyfructosylphenylalanine (a model substance not likely to be present in large quantities in foods) appears to depress the rate of protein synthesis in chicks (32) and to partially inhibit in vitro and in vivo the absorption of tryptophan in rats (33). The compound e-deoxyfructosyllysine inhibits the intestinal absorption of threonine, proline, and glycine and induces cytomegaly of the tubular cells of the rat kidneys (34) as does lysinoalanine. In parenteral nutrition the infusion of the various Amadori compounds formed during sterilization of the amino acid mixture with glucose is associated with milk dehydration in infants and excessive excretion of zinc and other trace metals in both infants and adults (35,36,37). 

It is conceivable that the reduced formation of tritiated water observed in scurvy could be due to a general reduction in protein synthesis, but this would not explain the marked differences between the specific activities of proline and hydroxyproline observed, nor would it explain observations in our laboratory that glycine and tyrosine are incorporated at rates similar to that of incorporation of proline into the collagen of granuloma obtained from scorbutic animals. 

According to this proposal, the incorporation of proline into collagen follows the acyl adenylate and acyl RNA stages now generally believed to occur in protein synthesis. A bound hydroxyproline intermediate is postulated, from which hydroxyproline is transferred to soluble RNA. We prefer to suggest that different RNA acceptor molecules exist for hydroxyproline and proline this would be consistent with recent work which indicates that the soluble RNA molecule contains the information for incorporation of a particular amino acid into protein (3). Although it is conceivable that there is hydroxylation of prolyl-sRNA to yield hydroxyprolyl-sRNA, an additional mechanism would be needed... 

Ornithine (a) and hydroxyproline (d) are both a-amino acids, because an amino group is attached to the same carbon atom as that which carries a carboxyl. Although ornithine is not used in protein synthesis, it is an intermediate in the urea cycle (Chap. 15). /3-Alanine (b) and y-aminobutyrate (c) have their amino group attached to a carbon atom different from that bearing the carboxyl, and are a /3- and a y-amino acid, respectively. Strictly speaking proline is a secondary amino acid, because the amino nitrogen is covalently connected to the side chain. It is sometimes referred to as an imino acid. 

GE2270A 394 is an antibiotic produced by Planobispora rosea ATCC 537731. It inhibits Gram-positive bacteria and anaerobes by acting on the protein synthesis elongation factor (EF) <1991JAN693, 1995T4867>. It contains proline, serine, glycine, two thiazolyl amino acids, and a heterocyclic centerpiece of a trisubstituted pyridine, all in a macrocyclic array. 

Protein synthesis in the body is constrained to 20 amino acids (including the imino acid proline), but modifications made after translation greatly extend the range of side chains found in mature proteins. Reversible modifications provide opportunities for regulation of protein function. 

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