Further studies on the amino acid composition of seed globulins.

Wit,h the recent import,ant advances in methods of analysis of amino acids, our knowledge of the composition of many types of proteins is being rapidly extended. Microbiological procedures which have come to the fore in recent years provide relatively simple and rapid methods of assay, but strict controls are necessary in order to secure satisfactory results. Frequent checks with protein preparations of known reproducibility and composition are eminently desirable. For this purpose, any one of a number of easily prepared cryst’alline globulins from plant seeds should provide satisfactory standards, particularly since these proteins are readily obtainable in large quantities, which is not the case with many of the most suitable animal proteins. We have found the seed globulins to be extremely useful for this purpose, and at the same time have extended our knowledge of the composition of these proteins. Data have recently been reported for the leucine, valine, phenylalanine, and tryptophane content of a group of seed globulins (Smith, Greene, and Bartner (1)). In t,his paper, attention will be given to the arginine, histidine, lysine, threonine, isoleucine, methionine, and cystine analysis of these proteins. The globulins of pumpkin and squash (Cucurbita moschata and Cu~curbita maxima), watermelon (Citrullus vulgaris), cucumber (Cucumis sativus), and, for comparison with these members of t.he Cucurbitaceae, edestin of hemp-seed and the globulin of tobacco seed were investigated. These proteins were all twice crystallized, and in some instances are the same preparations which have been analyzed previously (1, 2). In addition, control analyses were performed on a preparation of ,&lactoglobulin made in this laboratory. This protein was crystallized three times by Palmer’s method (3), and was homogeneous electrophoretically. The preparation contained 15.G5 per cent N (Dumas) when corrected for the ash and moisture content. All of the data presented below are for the anhydrous ash-free preparations.