EEC collaborative studies on a streamlined hydrolysate preparation method for amino acid determinations in feedstuffs

Evaluation of liquid chromatographic analysis of nutritionally important amino acids in food and physiological samples

Significant advances have been made in standardizing methods for amino acid analysis of foods. The methods included standardized hydrolysis of the food proteins followed by separation and quantitation of the released amino acids by ion-exchange chromatography (IEC). IEC is still the main method in use. Its use is, however, being replaced by the faster higher-performance liquid chromatographic (HPLC) methods of derivatized amino acids. The HPLC separation of precolumn phenylisothiocyanate (PITC) derivatives has been adapted for rapid analysis of all amino acids in protein hydrolysates (12 min) and nutritionally important amino acids in deproteinized physiological samples (20 min). The inter-laboratory variability of the PITC derivatization method has not been determined although the intra-laboratory variation of the HPLC method was found to be similar to that of IEC. When similar hydrolytic conditions were used in preparing protein hydrolysates, amino acid results obtained with the PITC derivatization method were generally in close agreement with those obtained by IEC. There is, however, room for improvement in the HPLC analysis of amino acids in physiological samples.

Phylogeny congruence analysis and isozyme classification: the pyruvate kinase system

As the isozymes of pyruvate kinase (PK) are best known in rats, the characteristics of the rat isozymes are generally used to classify the PK isozymes in other species. Given the discrepancies generated by this classification by analogy, we evaluated a classification using a phylogeny congruence analysis of the compositional relatedness of vertebrate PK's. While our phylogenetic analysis confirmed the well established separation of the L and R isozymes from the K and M isozymes, its power became most evident in the identification of non-orthologous (or variant) forms of PK. Our analysis emphasized the uniqueness of chicken liver PK which cannot be classified either as a K or an L isozyme, confirmed that tumors express a variety of forms of PK, and indicated that lungs systematically express PK's which are not orthologous with PK's from other tissues. The determination of orthology by the phylogeny congruence analysis assumes that the structural data from different sources are subject to similar methodological error. However, we cannot reject the possibility that an apparent lack of orthology be due to artifacts during purification and analysis.

General problems associated with the analysis of amino acids by automated ion-exchange chromatography

Some of the general problems commonly encountered with the analysis of amino acids have been described. These include problems associated with the preparation and storage of samples prior to analysis and those associated with the analytical stage itself. The effects on the accuracy of the determination of amino acids have been discussed, together with possible solutions to some of the problems.