Hydroxyprolin

Pa.g et s Disease of Bone. Paget s disease, osteitis deformans, occurs mainly ia people over 40. About twice as many men as women are affected. The disease, caused by faulty utilisation of may be mild and asymptomatic requiring Httle or no treatment. Clinical signs are high alkaline phosphatase and high urine hydroxyproline as weU as abnormal bone stmcture which usually goes unrecognised until discovered accidentally by routine x-ray examination (32). 

Hydroxylated amino acids (eg, 4-hydroxyproline, 5-hydroxylysine) and A/-methylated amino acids (eg, /V-methylhistidine) are obtained by the acid hydrolysis of proteins. y-Carboxyglutamic acid occurs as a component of some sections of protein molecules it decarboxylates spontaneously to L-glutamate at low pH. These examples are formed upon the nontranslational modification of protein and are often called secondary protein amino acids... 

Thin-Layer Chromatography (tic). Tic (126) is used widely for quahtative analysis and micro-quantity separation of amino acid mixtures. The amino acids detected are developed by ninhydrin coloring, except for proline and hydroxyproline. Isatia has been recommended for specific coloring of pToline (127). 

Figure 14.1 Each polypeptide chain in the collagen molecule folds into an extended polyproline type II helix with a rise per turn along the helix of 9.6 A comprising 3.3 residues. In the collagen molecule three such chains are supercoiled about a common axis to form a 3000-A-long rod-like molecule. The amino acid sequence contains repeats of -Gly-X-Y- where X is often proline and Y is often hydroxyproline. (a) Ball and stick model of two turns of one polypeptide chain.

Fig. 1 Reflectance scan (A) and fluorescence scan (B) of a chromatogram track with 50 ng of each amino acid per chromatogram zone hydroxyproline (1), proline (2).

The chromatograms stained with ninhydrin are immersed in the reagent solution for 1 s or sprayed evenly with it and then placed in the free half of a twin-trough chamber containing 25% ammonia solution. Apart from proline and hydroxyproline, which yield yellow copper complexes, all the amino acids yield reddish-colored chromatogram zones [3],... 

Ornithine, proline, hydroxyproline, pipecolic acid and sarcosine yield red zones, glycine greenish-brown and the other amino acids weakly brown ones [3]. The colors of the zones are different if an alcoholic solution of potassium carbonate is used for basification instead of dipping solution II. 

FIGURE 4.4 The structures of several atniuo acids that are less cotntnou but nevertheless found in certain proteins. Hydroxylysine and hydroxyproline are found in connective-tissue proteins, pyroglutatnic acid is found in bacteriorhodopsin (a protein in Halohacterium halohium), and atninoadipic acid is found in proteins isolated from corn. 

The tendencies of the amino acids to stabilize or destabilize a-helices are different in typical proteins than in polyamino acids. The occurrence of the common amino acids in helices is summarized in Table 6.1. Notably, proline (and hydroxyproline) act as helix breakers due to their unique structure, which fixes the value of the —N—C bond angle. Helices can be formed from either... 

In a study of the deprotection of the MEM ethers of hydroxyproline and serine derivatives, it was found that the MEM group was stable to conditions that normally cleave the t-butyl and BOC groups [CF3COOH, CH2CI2, 1 1 (v v)]. The MEM group was also stable to 0.2 N HCl, but not stable to 2.0 N HCl or HBr-AcOH. ... 

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