Protein synthesis: are there real species differences?

One of the major factors in the nitrogen metabolism of animals is the phenomenon of protein turnover i.e. the continual breakdown and synthesis of body protein, the resultant of which is protein deposition. The measurement of these processes has consequently attracted much interest although, for reasons of technique, attention has focused upon measurements of protein synthesis, protein breakdown being calculated from simultaneous measurements of growth and protein synthesis (Picou & Taylor-Roberts, 1969; Turner & Garlick, 1974; Golden et al. 1977). In this sense, the following paper will be no exception in its emphasis upon measurements of protein synthesis. The large majority of publications upon protein synthesis in vivo have been concerned with experiments in the rat and by and large these have concentrated upon individual tissues (although see Garlick et al. 1973, 1975; Lobley, Webster et al. 1978) in a wide variety of circumstances. Although there are available in the literature values for protein synthesis in various tissues in other species (Garlick et al. 1976; Nicholas et al. 1977; Buttery et al. 1977; Amal, 1977; Edmunds et al. 1978; Simon et al. 1978; Lobley, Reeds et a1. 1978) in general these have been obtained at one age and at a defined single intake of food. In all these studies the same general conclusions have been drawn i.e. that the fractional rate of protein synthesis (protein synthesis per unit time+amount of protein in tissue) in skeletal muscle is low and in the visceral tissues it is high, although there is some controversy over the relative contributions of different tissues to total body protein synthesis (discussed in Lobley et al. 1980). In contrast to these reports of ‘static’ measurements, information on protein turnover in man has been obtained under a variety of conditions (e.g. obesity, severe under-nutrition, injury and infection) but the large majority of studies have concentrated upon measurements of protein synthesis in the whole body (see Waterlow et al. 1978 for extensive review). It is difficult, therefore, to make many meaningful interspecies comparisons, particularly if interest is to be centred upon the responses of different species to