The Chemistry and Metabolism of the Compounds of Sulfur

Abstract: Publisher Summary This chapter discusses naturally occurring peptides, which allows several generalizations concerning their importance as distinct chemical entities. Certain physiologically active naturally occurring peptides seem to be linked to the much larger protein molecules with respect to their structure and physiological activity. The distinction is based largely on the fact that naturally occurring peptides are composed of amino acids with uncommon configurations and structures, and of linkages other than the classical peptide bond. The uncommon structures exist only rarely in proteins and this would be exactly why one can use them to differentiate the naturally occurring peptides from protein fragments. One group, containing heteromeric peptides, is characterized on the basis of a common structure and an identical amino acid composition, differing from one another by the nature of the heteromeric group. Such is the case of the penicillins. Another group also has a given identical structure, but each member of the group has a different amino acid composition. All the members of such families possess the same number of amino acids, however, are of a different nature. All the members of another group possess the same heteromeric groupings and uncommon amino acids, but they differ by the number and nature of other amino acids. The characteristic biological actions of the naturally occurring peptides are because of their uncommon structures and compositions. The biological activity is related to the structure. The existence of naturally occurring peptides show that nature utilizes amino acids to build proteins and peptides.

Abstract: Anyone who has had occasion to isolate luminous bacteria can readily understand why these organisms have received so much attention from microbiologists of the present and of the last centuries The aesthetic satisfaction derived from the contemplation of these beautiful organisms repays the investigator many fold for the hours spent in darkness and seclusion vis a vis some fetid putrefying fish. Due partly, no doubt, to this fact, a voluminous literature dealing with these bacteria has accumulated. For an excellent bibliography and a review of all the most important contributions to the knowledge of the luminous bacteria and to the understanding of the physiology of luminescence, reference need only be made to Pratje (1923) and Harvey (1940, 1941). Owing to the recognition that the light-emitting process is a by-path of respiration, and to the convenience of using changes in the intensity of luminescence as an indicator of physiological events in the organisms, the luminous bacteria have acquired, in the last few years, a new importance in scientific research, as material for exceedingly interesting experiments on general physiological problems. (E.g., Johnson, 1938, 1939.) Little attention, however, has been devoted to the natural history of this group of bacteria since Beijerinck's studies (Beijerinck, 1889, 1912, 1916). Although innumerable species have been described, no thorough systematic study of the group has ever been undertaken with a view to clarifying their relationship among themselves or with other bacteria. In the hope of contributing to the elucidation of some of the complex taxonomic and physiological problems involved in the sudy of this group of organisms and to the better understanding of some previously recorded observations on the behavior of the bacteria under certain conditions, a series of investigations has been carried out on the nutrition and metabolism of several species, the results of which seem to be of sufficient general interest to warrant their publication. In the present paper, the results of experiments on growth requirements of a number of strains will be presented.