Proline, incorporation

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). 

Krolak JM, Taylor N, Dashek WV, Mills R. Azetidine-2-carboxylic acid-induced suppression of 14C-proline incorporation into cytoplasmic macromolecules and cell wall of Lilium longiflorum pollen, in Advances in Plant Reproductive Physiology (Malik CP, ed.), Kalyani Publishers, New Delhi, India, 1978, pp. 62-71. 

Phenanthroline inhibits proline incorporation into proteins.391,392 Benzo-substituted-l,8-phenanthrolines and 1,10-phenanthrolines are amoebicides.180 l,8-Phenanthroline-8-oxide has a wide spectrum of antibacterial activity.393... 

Phenanthroline has been reported to inhibit proline incorporation into proteins.391... 

Phenanthroline like 1,10- and 1,7-phenanthrolines has anticancer properties.374 The toxic effects of phalloidine, an isolate of the fungus Amanita phalloides, are inhibited by 4,7-phenanthroline.536 4,7-Phenanthroline also inhibits proline incorporation into proteins.391,392 3-Methyl-4,7-phenanthroline has been suggested as a diagnostic agent for assisting in the detection of blood in body fluids.537... 

The alkaloid colchicine binds tightly to tubulin and this characteristic has been used (Fig. 6.1) to isolate a tubulin-like fraction from H. diminuta, with properties similar to tubulin from other organisms. Furthermore, colchicine affects the qualitative distribution of [3H]proline-incorporated protein in this worm, with label accumulating in the parenchyma (195). This suggests that colchicine inhibits translocation in the tegument and provides evidence that microtubules within the internuncial processes facilitate movement of cell products from tegumentary cytons (Chapter 2) to the body surface for subsequent release. 

As indicated in Figure 2, when minces of tumor obtained from normal and ascorbic acid-deficient animals were incubated with C14-pro-line, much more radioactivity was incorporated into the collagen of the normal tissue. When the specific radioactivities of the isolated imino acids were examined (Table HI), several conclusions were possible. In the experiments with granuloma from normal animals and C14-proline, the values for hydroxyproline were not far from those of proline. With the scorbutic granulomas, the specific activity of the isolated proline was not greatly reduced, compared to that obtained from the normal granuloma. In contrast, the specific activity of the hydroxyproline isolated from the deficient tissues was markedly reduced. Similar results were obtained in the studies with tritiated proline. Thus, the specific activity of the proline isolated from the deficient granuloma was only moderately reduced, whereas the specific activity of the hydroxyproline was extremely low. This observation may be explained in terms of a dual-pathway mechanism of proline incorporation, considered below. 

In 2006, Lectka and coworkers upgraded the enantioselective a-bromination with (R)-prolinc incorporated cinchona catalyst 129 and new bromination agent 127 (Scheme 6.38) [67]. It was notable that (R)-proline incorporated cinchona catalyst gave quite higher enantioselectivity (95% ee) than that of (S)-proline incorporated cinchona catalyst (88% ee) and their previous catalyst 122 in a-bromination of phenylacetyl chloride. 

Pig. 4. Inhibition of prolyl-tENA synthesis by and y-thiaproline.Pull circles synthetases and tENAS from rat liver full line -thiaproline broken line y-thiaproline.Empty circles synthetases and tENAs from E.colij j3- and y-thiaproline gave the same values.Relative proline incorporation = ratio of the amount of tRNA-bo ind " C-proline in the presence of the analogs to the amount in their absence. Experimental details in (56). 

Overall the results obtained with 8-thiaproline showed that it acts as a competitive inhibitor of proline,but differs somewhat from the other proline analog, y-thiaproline. We may distinguish between the E.coli and the mammalian systems. In E.coli -thiaproline has a higher affinity than y-thiaproline for the aminoacyl-tENA synthetases on the other hand it is bound to tRNAP o at the same extent as y-thiaproline. -Thiaproline shows a more evident inhibition on the proline incorporation into polypeptides,and this may reflect a higher capacity of j3-thiaprolyl-tRNA with respect to y-thiaprolyl-tENA to compete with prolyl-tEEA at ribosomal level. 

The one exception is proline, a secondary anine in which the amino nitrogen is incorporated into a five-rnernbered ring. 

In addition to effects on biochemical reactions, the inhibitors may influence the permeability of the various cellular membranes and through physical and chemical effects may alter the structure of other subcellular structures such as proteins, nucleic acid, and spindle fibers. Unfortunately, few definite examples can be listed. The action of colchicine and podophyllin in interfering with cell division is well known. The effect of various lactones (coumarin, parasorbic acid, and protoanemonin) on mitotic activity was discussed above. Disturbances to cytoplasmic and vacuolar structure, and the morphology of mitochondria imposed by protoanemonin, were also mentioned. Interference with protein configuration and loss of biological activity was attributed to incorporation of azetidine-2-carboxylic acid into mung bean protein in place of proline. 

Figure 28-11. The prolyl hydroxylase reaction. The substrate is a proline-rich peptide. During the course of the reaction, molecular oxygen is incorporated into both succinate and proline. Lysyl hydroxylase catalyzes an analogous reaction.

Other potent peptide mimetic NS3 protease inhibitors have been reported that incorporate a serine trap on the C-terminal end of the peptide. Thus, the inhibitory activity of telaprevir (VX-950, 59), (7nM vs. NS3, 300 nM vs. the la replicon) is based on truncation of the polypeptide substrate, maximizing binding by alteration of amino acids at the scissile site, and capping both N- and C-terminal ends, the latter with a known dicarbonyl serine trap. This compound has exhibited impressive antiviral activity in animals, and showed a 4.4 log drop in viral load in genotype 1-infected patients in a Phase lb clinical trial [110]. Telaprevir is expected to enter Phase 3 clinical trials in 2007. Additional bicyclo-proline-based P2 tetrapeptides, represented by analog 60 (Kj = 22 nM), have been explored. Although the compounds are selective inhibitors of NS3, little or no cell-based replicon activity was reported, presumably due to poor cellular permeability [111-114], A diastereomer of telaprevir, has been reported to inhibit the replicon with an EC50 of 0.55 pM [115]. 

Efforts to find potent and selective DPP-4 inhibitors in the a-amino acid amide series were made in parallel with those in the (3-amino acid amides series. The structural origin of the earliest P-amino acid amide DPP-4 inhibitors traces back to two Merck HTS hits proline derivative 25 and piperazine derivative 26. These two screening leads were further progressed to P-amino acid amide DPP-4 inhibitors incorporating thiazolidine, proline and piperazine amide moieties (Figure 17.5). 

---