Determination of methylated basic, 5-hydroxylysine, elastin crosslinks, other amino acids, and the amino sugars in proteins and tissues☆☆☆

Abstract Analytical single-column chromatographic methods have been developed for determining all methylated basic amino acids, isodesmosine, desmosine, the amino sugars glucosamine and galactosamine, the diastereoisomers of 5-hydroxylysine, and related compounds at picomole levels in protein and tissue hydrolysates. Complete resolution of all these unique basic amino acids as discrete peaks was achieved in 5.4 h on a 50 × 0.28-cm microcolumn of Dionex type DC-4A spherical resin (9.0 ± 0.5 μm) using updated instrumentation commonly available for amino acid analysis. The column was operated at 5.65 ml/h with two 0.35 m sodium citrate buffers (pH 5.700 and 4.501), at two temperatures (31.5 and 73°C). Excellent resolution of all ω- N -methylarginines and related compounds was also achieved in 3 h using a 17.5 × 0.28-cm microcolumn of Dionex DC-5A resin (sized to 6.0 ± 0.5 μm), two citrate buffers (0.21 m Na + , pH 5.125; 0.35 m Na + , pH 5.700), a buffer flow rate of 5.75 ml/h, and a temperature of 52°C. Complete separation of all other amino acids found in protein or tissue hydrolysates including S -carboxymethyl cysteine, 4-hydroxyproline, methionine S,S -dioxide, and the amino sugars was also carried out in 95 min using a 23.5 × 0.28-cm microcolumn of Dionex DC-5A resin. The use of purified microcolumn buffers gave smooth baselines without interference from artifacts or minor hydrolysate components. The major advantages of these methods are: first, their high resolving power; second, their high sensitivity which is comparable and in some aspects superior to the newer instruments; and third, their high reproducibility (100 ± 2.5%) and low operating costs. These methods should be especially valuable for determining myosin, actin, and elastin in tissue hydrolysates from the amounts of N τ -methylhistidine, desmosine, or isodesmosine present, respectively, and for studying protein methylation, hydroxylation, crosslinking formation, and the turnover rates of contractile and connective tissue proteins in biological systems.