Halogenated and nitrated derivatives of tyrosine

A common finding, if proteins are hydrolyzed with undistilled HCl or 

Sanger and Thompson (1963) also reported the high voltage electrophoretic migrations of the halogenated derivatives at pH 1.85 (2 % formic acid, 8 % acetic acid, 1 hr at 4000 volts this system should be comparable to the pH 1.9 electrophoresis described in the Appendix). All migrate slower than tyrosine in this system tyrosine, 22.5 cm 3-chlorotyrosine, 19.3 cm 3,5-dichlorotyrosine, 16.5 cm 3-bromo-tyrosine, 18.0 cm 3,5-dibromotyrosine, 14.8 cm 3-iodotyrosine, 

0 cm 3,5-diiodotyrosine, 13.0 cm and 3-chloro-5-bromotyrosine, 15.7 cm. The migrations in pH 8.9 electrophoresis are also reported. Nitrotyrosine has a migration of 0.87 compared to 1.00 for tyrosine in pH 1.9 electrophoresis. It should be noted that these derivatives have lower color values than tyrosine and that quantitation is generally not good after acid hydrolysis. 

During acid hydrolysis of proteins, valine and isoleucine are often released more slowly than other amino acids due to steric hindrance of hydrolysis by the / -branched sidechains. The Ile-Ile bond is particularly resistant to hydrolysis and is cleaved to the extent of about 50% in 24 hr at 110°C. This could mislead an investigator into the belief that one residue of isoleucine was present in a given peptide rather than two. The Val-Val, Val-Ile and lle-Val bonds are also slowly hydrolyzed, being 60-75 % cleaved in 24 hr at 110°C. Therefore, if the amounts of valine and isoleucine appear to reach a plateau after 72 hr of hydrolysis, these values may be used otherwise, hydrolysis for 120 hr may be required to obtain quantitative values. Small amounts of u/loisoleucine, which elutes from most analyzer columns just before isoleucine, should be included in the isoleucine determination. 

---