摘要:

SummaryThe final stages in the formation of protein, rather than the formation of amino‐acids, are discussed. The approach is physiological rather than biochemical. After reviewing the present state of knowledge of the structure of proteins various suggestions as to the substances used in the formation of the protein are considered. The evidence seems to be in favour of the formation by condensation of amino‐acids rather than by the polymerization of some simple unit. This leads to a consideration of the various seats of synthesis in the cell and to the mechanism by which the proteins are formed from their constituent parts. The article concludes with a discussion of the interrelation of nitrogen metabolism and respiration and of the factors governing amino‐acid formation and protein synt

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1943.tb00292.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

SummaryThe principal feature of recent studies on the nutrition of the Protozoa has been the development of culture media suitable for the maintenance of several score of species in ‘pure culture’. As investigators approached precise definition of the constitution of the culture media the significance of ‘trace elements’, accessory food factors and the like became more apparent. The types of culture apparatus, the methods of sterilization of organism and medium, the proceduresofestimating growth of populations, and the exact composition of reagents have all been found to be of greater importance than originally realized. Within the phylum there exist chlorophyll‐bearing, plant‐like forms and numerous intermediary types up to and including those requiring living particulate food, thus providing the full range of nutritional types. The older systems of physiological classification have been extensively revised, but none of those proposed is adequate. In some instances the relations between variations in cytoplasmic structure (plastids) and nutritional requirements have been demonstrated.Many species of chlorophyll‐bearing and colourless flagellates have been studied. Intensive work onPolytoma, ChilomonasandEuglenahas revealed notable species and strain variations with respect to factors such as fatty acid metabolism, nitrogen requirements, the effects of light on nutrient requirements and on response to plant hormones and vitamin constituents. The effect of systematic modification of chemical structure on the utilization of vitamin components has been studied for some species. A few dozen of the normally phagotrophic (holozoic) forms have been grown in the absence of other living forms (pure liquid culture), while certain forms have been grown on single species of food organisms (pure mixed culture) or on dead food organisms. With the exception of certain amoebae the salient work on pure culture has been carried out with the smaller ciliates, particularlyGlaucoma.The media employed (protein hydrplysates, tissue autolysates, etc.) are chemically and physically highly complex. Such media contain labile constituents susceptible to important changes when subjected to minor procedural variations. Analyses of the media before and after the growth of organisms have given some indications of the nature of the nitrogenous fractions metabolized. The accessory growth‐factor requirements of these forms are complex. The very specialized nutrients required by parasitic forms have demonstrated interesting evolutionary relationships. An increasing number of biochemical experiments is being reported on the existence of various enzyme systems in the Protozoa. Our knowledge, however, of the metabolism of representative Protozoa rema

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1943.tb00293.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY

摘要:

SummaryBiological races are defined as such subdivisions of a morphological species as are distinguishable by differences in biological characters only. Though biological races are well represented in diverse groups of parasitic Protozoa, their true nature is in most cases concealed under separate specific names.In parasitic Protozoa biological races differ from each other in various aspects of their host‐parasite relations. These may be manifested in host‐restriction (or host‐specificity), as in trypanosomes of thebruceigroup, containing races confined to man and to other mammals; in intestinal amoebae and flagellates comprising human and batrachian races; and in human and simian malaria parasites (Plasmodium). Likewise, races parasitic in the same vertebrate host may be restricted to distinct vectors, as in piroplasms (Babesia) of cattle and dogs.There are races which cause different diseases in the same host, usually with a distinct localization in its tissues, e.g.Leishmaniain man and dogs, and trypanosomes of theevansigroup, causing dourine and surra. Others again vary in the degree of virulence to the host, e.g. piroplasms of the generaTheileriaandBabesia.A variation in pathogenicity to one or more hosts characterizes some geographical races of the same parasite, e.g. local strains of humanPlasmodium, and ofTrypanosoma evansi.Finally, in certain races various differential characters may be combined.Variations in the host‐parasite relationship, as manifested by different races of Protozoa, are determined by the degree of their adaptation to the physical and chemical conditions in the host. These conditions include, among others, body temperature, quality of the digestive juices, nutrition (diet), and properties of the serum (parasiticidal action). The mutual adaptation of parasite and host involves reciprocal reactions, among which the serological reactions of the host are especially interesting, for they throw light on the intimate constitution of parasitic microorganisms. There is reason to believe that biological races of some parasitic Protozoa‐like the intraepecific ‘types’ of bacteria‐differ from each other in antigenic composition, while retaining common antigens characteristic of the species as a whole. Antigenic constitution is, therefore, correlated with the biological peculiarities of these races (at least in blood parasites), and since antigens consist of qualitatively different chemical substances, the distinction between biological races resolves itself into differences in the chemical structure of the antigenic components of the organisms in question. Biological races in parasitic Protozoa appear to be stable and hereditarily fixed. The biological criteria for their differentiation and the constancy of their diagnostic characters are advanced as arguments in support of an independent taxonomic status for b

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1943.tb00294.x

出版商:Blackwell Publishing Ltd    

年代:1943

数据来源: WILEY