Thialysine

Other radicals could not be detected directly by EPR, because of their instability. By use of analogous molecules which stabilize these radicals, however, their existence was rationalized. Stabilization of an a-lysyl radical analog was achieved by use of 4-thialysine 32 [40] (Scheme 1.6.8), with trans-4,5-dehydrolysine [41] as substrate. 

Scheme 1.6.8. Incubation of 4-thialysine with lysine 2,3-aminomutase generates 4-thialysyl-PLP radicals.

Figure 6. Effects of and at C3 of 4-thialysine on the EPR spectra at the active site of LAM. Procedure as in Figure 4, with 4-thialysine in place of lysine. A, 4-thialysine B, 4-thia[3- H2llysine C, 4-thia[3- C]lysine. Adapted from reference 22 with permission from the American Chemical Society.

THIALYSINE, THIAISOLEUGINE AND THIAPROLINE AS INHIBITORS IN PROTEIN SYNTHESIZING SYSTEMS... 

It was also shown that thialysine may be acetylated on the terminal amino group by some microrganisms(9-11) Thialysine may be cleaved non enzymatically by pyridoxal phosphate through an a- elimination giving cysteamine, ammonia and pyruvate(12). It has to be recalled that thialysine may be synthesized from serine and cysteamine by yeast serine sulfhydrase(15) ... 

Recently we had the opportunity to test the activity of thialysine in protein synthesizing systems from either E.coli,rat liver and rabbit reticulocytes,in a study directed to investigate the activity of another lysine analog,selenalysine(22). It was first studied the activation of thialysine by E.coli and rat liver amino-acyl -tRNA synthetases,by assaying either the ATP-PPi... 

In the ATP-PPi exchange with both E.coli and rat liver synthetases the Km values obtained with thialysine as substrate were similar to those of lysine,as shown in Table I. On the contrary the V values for thialysine were in both systems around forty per cent of that of lysine. When lysine and thialysine were present together in 1 1 molar ratio,the obtained V value indicated that lysine and thialysine are activated by the same enzyme. 

Km and V values for lysine and thialysine in the ATP-PPi exchange reaction.Experimental details in(22).V values expressed as per cent of those obtained with lysine. 

Further the effects of thialysine on lysine or leucine incorporation into polypeptides were studied,using polypeptide synthesizing systems from E.coli,rat liver or rabbit reticulocytes. It was shown that in all three systems thialysine inhibits incorporation of labelled lysine into polypeptides,whereas it is without effect on leucine incorporation. The results obtained are reported in Table II. 

Fig.1. Inhibition of lysyl-tENA synthesis by thialysine. Synthetases and tENA from E.coli(full line) or from rat liver(Broken line).Relative lysine incorporation = ratio of the amount of tENA-bound l C-lysine in the presence of thialysine to the amount in its absence.Experimental details in(22).

Per cent of inhibition of lysine or leucine incorporation into polypeptides by thialysine.Experimental details in... 

M. Fabry, P. Hermann and I, Rychlik. Poly(A)-directed formation of thialysine oligopeptides in E. coli cell-free system. Collection Czechoslov. Commun., 1977, 42 1077. 

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