Pyrolysis Gas Chromatography of Wool

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Abstract
Although determination of tyrosine and most other amino acids is straightforward by conventional methods of amino acid analysis, determination of tryptophan is dif ficult and time-consuming due to its sensitivity to acid-catalyzed protein hydrolysis. Pyrolysis gas chromatography (Py-GC) therefore was investigated as an alternative method for tryptophan analysis. Py-GC revealed that wool gives rise to indole and skatole from degradation of its tryptophanyl residues, along with phenol' and para- cresol from its tyrosyl residues. To test Py-GC for determining tryptophan content relative to tyrosine content, mixtures of poly-tryptophan and poly-tyrosine were used to establish a linear relationship between the peak area ratio indole/(phenol + para- cresol) and the tryptophan / tyrosine molar ratio (Trp/Tyr). The polypeptide data were supplemented with data from pyrolysis of several proteins of known Trp/Tyr ratio. The supplemental data also were used to confirm the utility of the linear rela tionship in deriving a Trp/Tyr ratio for an unknown protein. The accuracy of the derived Trp/Tyr ratio diminished somewhat when the tryptophan content was low; using Py-GC, wool was predicted to have one tryptophan for every eight to nine tyrosines, as opposed to one for every seven tyrosines using conventional amino acid analysis. The method permitted facile monitoring of tryptophan degradation in wool during treatment with dimethyl sulfoxide in hydrochloric and acetic acid. There also was a strong indication of tryptophan degradation during wool carbonizing.