The Analysis of the Alcohol-insoluble Nitrogen of Plants by Quantitative Procedures based on Paper Chromatography

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Abstract
Part I. The amino-acid composition of egg albumin, zein, edestin, cucumber (Cucumis) seed globulin, and squash (Cucurbita) seed globulin has been determined by a quantitative paper chromatographic method. The chromatographic analyses account completely for the amino-acid nitrogen of the protein hydrolysate as determined by the Kjeldahl method. More complete analyses than hitherto of cucumber and squash seed globulin have been obtained. These analyses can now be regarded as complete since histidine and tryptophane, which have not been determined chromatographically, have previously been reported. The two cucurbit seed globulins analysed closely resemble edestin, and evident differences between these three on the one hand and zein on the other are referred to in the text. It is evident that the paper chromatographic method is applicable to the quantitative amino-acid analysis of the protein-N fraction of the plants as well as to the analysis of pure proteins. Part II. The analysis of the alcohol-soluble and insoluble fractions (hydro-lysate) of potato tubers of the variety ‘Sebago’ has been carried out. Attention is drawn to differences which exist between the samples and varieties which have been investigated, namely ‘King Edward’, ‘Sebago’, and ‘Katahdin’. These differences relate particularly to the relative proportion of soluble to insoluble nitrogen, to the amount of amides present in the soluble fraction, and to the ratio of asparagine to glutamine. There is no correlation between the relative proportions of amino-acids as they exist free in the tuber and as they occur in the alcohol-insoluble (protein) fraction. Certain compounds (e.g. γ-aminobutyric acid) are present free in the tissue, but they do not occur in the protein. Also the amides far exceed their possible occurrence combined in the protein. Proline especially is much more abundant in the combined than in the free state, and the ratios between the various free amino-acids are quite different from those which apply to the protein. The latter data suggest that the soluble compounds which occur free are not directly combined as such to form protein. The utility of the quantitative procedure based on partition chromatography on paper in the analysis of the alcohol-insoluble (protein) fraction of plants is, therefore, established.

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