Protein synthesis rate

Simon M, Azam F (1989) Protein content and protein synthesis rate of planktonic marine bacteria. Mar Ecol Progr Ser 51 201-213... 

Figure 30.3 Difference between nitrogen uptake and growth kinetics from experiments, after Zehr et al. (1988). Short-term uptake kinetics (A) are driven by membrane transport processes, and usually exceed assimilation and incorporation into protein. Short-term uptake declines as feedback from internal pools and regulatory mechanisms are affected by influx of N. (B) Longer term N uptake is driven by protein synthesis rate, which is equivalent to the growth rate. (C) Model of competition between two species showing that competition can be affected by both transport and growth.

In another study, Lin et al.46 reported that there was a depressive effect of tryptophan deficiency on protein synthesis rate in pig muscle. Also, earlier studies revealed that, among the essential amino acids, tryptophan was one of the most critical at weaning on the effect of its deficiency on the appetite of piglets47 in the same way that its deficiency affected the appetite of older pigs.48... 

Ponter et al.135 reported that in piglets the fractional protein synthesis rates were generally not increased in duodenal or jejunal mucosa by adequate or excess tryptophan in high carbohydrate or high fat diets, although in stomach small increases occurred. Also, the fractional protein synthesis rate was increased with adequate or excess tryptophan diets compared to inadequate tryptophan diets (controls). 

Ponter et al.135 reported an increase in fractional protein synthesis rate in the skin of piglets tube-fed adequate or excess tryptophan diets compared to controls (tryptophan-inadequate diet). 

Lin et al.137 reported that there was a depressive effect of tryptophan deficiency on the protein synthesis rate in pig muscle. Also, Cortamira et al.138 reported that the fractional protein synthesis rates in piglet muscle (longis-simus dorsi and semitendinosus) were increased in animals fed tryptophan-adequate diets compared to controls (tryptophan-inadequate diets). This was confirmed in a later study by Ponter et al.135... 

TRANSLATIONAL CONTROL Eukaryotic cells can respond to various stimuli (e.g., heat shock, viral infections, and cell cycle phase changes) by selectively altering protein synthesis. The covalent modification of several translation factors (nonribosomal proteins that assist in the translation process) has been observed to alter the overall protein synthesis rate and/or enhance the translation of specific mRNAs. For example, the phosphorylation of the protein eIF-2 affects the rate of hemoglobin synthesis in rabbit reticulocytes (immature red blood cells). 

Endo and co-workers at Ehime University, Matsuyama, Japan, have led the development of the most promising eukaryotic cell-free system to date, based on wheat embryos. A significant advance made by this group was the development of pEU expression vectors that have overcome many of the difficulties associated with mRNA synthesis for translation in a eukaryotic system [8]. In addition to extensive optimization of reaction conditions that have seen improvements in protein synthesis rates, Endo and colleagues have improved wheat extract embryo preparation protocols to enhance the stability of these systems to a remarkable extent [9]. When coupled with the dialysis mode of reaction, Endo et al. were able to maintain translational activity in a coupled transcription/ translation wheat embryo reaction for 150 hours, producing 5 mg of enzymatically active protein per mb reaction mixture [10]. This again represents a serious alternative to in vivo methods of large-scale protein production. 

For quantitation of viral and cellular parameters, cell suspensions (in triplicate) were collected, pooled, and centrifuged at 1400 X g for 10 min at 4°C. Supernatant was used for assays of extracellular reverse transcriptase (RT) activity and p24 antigen. Cell pellets were used for the determination of cellular metabolic activity and protein synthesis rates. 

Fig. 5. Determination of protein synthesis rates in H9 ceils in the presence and absence of ascorbate (AA). Protein synthesis was assayed as described by Somasundaran and Robinson (17). Each point is the mean of S-labeled amino acid incorporation per 10 cells.

This example from the tissues of rainbow trout is drawn from data from animals that were denied food for 12 h. In view of the variation in synthesis rates with nutritional status (see below) it is possible that not only will the intercepts of the body weight/protein synthesis rates relationships change with nutritional status but also the slopes of the lines. 

It has been suggested that the postulated high protein synthesis rates of larval fish may be due to the relatively high proportion of the body occupied by the intestine which will have a high rate of synthesis relative to the white muscle (Dabrowski 1986 Weatherly and Gill 1987). Thus as body size increases not only may fractional rates of protein synthesis of individual tissues decline but also the relative proportions of the body may change with a relative increase in slowly synthesising white muscle. 

When rainbow trout have been denied food for 6 days, meals bring about a post-prandial surge in protein synthesis in all the tissues (McMillan and Houlihan 1988). The time course of the protein synthesis response appears to be tissue-specific. Tissue protein synthesis rates in the ventricle and red and white muscle exhibited a graded response where a single meal resulted in synthesis rates lying between the fasted and continually fed states. The gill, stomach and intestine responded with a rapid rise within 3 h to the levels found in continually fed fish and this stimulation was maintained. The liver demonstrated a transient increase in protein synthesis which reached a peak at 3 h, which subsequently declined. Subsequent analysis has revealed that the peak found in the liver occurred within 1 h of the meal (McMillan and Houlihan 1989). A stimulation of muscle protein synthesis has been found in salmon 9 h after feeding (Fauconneau et al. 1989). 

The oxygen consumption of the crab Carcinus increased twofold at 3 h after the meal and returned to its previous value within 24 h. The whole body protein synthesis rates of animals fed similarly sized meals paralleled the oxygen consumption changes protein synthesis rates increased twofold by 3 h after the meal and remained elevated for 16 h (Fig. 5). 

Thus far, these results indicate that there are post-prandial surges in protein synthesis, with different tissues responding to the meal at different times. The whole body protein synthesis rates rise and fall after a meal with a pattern similar to the post-prandial increases in oxygen consumption. The whole body response to a meal appears to be an amalgam of the individual tissues which are responding to the meal with differing time courses. 

The different muscle fibre types of fish may be cited as examples of tissues with widely differing fractional protein synthesis rates cardiac muscle has often been found to have fractional protein synthesis rates which are approximately four fold higher than those of white muscle fibres (Haschemeyer et al. 1979 Smith et al. 1980 Fauconneau 1985 Houlihan et al. 1986 Houlihan et al. 1988b McMillan and Houlihan 1988). 

Short-term starvation in rainbow trout results in a reduction in the rates of synthesis of the whole muscles and the individual fractions and a decrease in the cytochrome oxidase activity (unpubl. results). In a similar manner, rates of synthesis of mammalian myofibrils have been found to be markedly sensitive to nutrition (Bates and Millward 1983). There have been a number of papers which have shown a correlation between the nutritional state of fish and the levels of glycolytic and oxidative enzymes (Sullivan and Somero 1983 Goolish and Adel-man 1987) and it will be of interest to correlate plane of nutrition, whole muscle and mitochondrial protein synthesis and enzyme activities. The correlation between RN A concentration and protein synthesis rates discussed below suggests that we are witnessing a number of nutritionally controlled parameters which are operating in concert increasing, for example, the aerobic scope of the tissues and their scope for protein synthesis. 

Fractional growth rates (kg) and protein synthesis rates (k ) for various tissues of trout, cod, crab... 

It is likely that the ranking of the tissues in terms of their protein synthesis rates will be paralleled by their rates of oxygen consumption (suggested for fish from the data of Oikawa and Itazawa 1984) and protein synthesis rates are also closely correlated with RNA concentrations in the tissues (see below). 

It had been thought that the protein synthetic rates of some tissues (e.g. liver and gill) of fish would be resistant to starvation such tissues have been described as regulatory (Fauconneau 1985). In contrast, red and white muscle respond to starvation by a reduction of the rate of protein synthesis (e.g. Loughna and Goldspink 1984). However, as has been described above, there is now evidence that nutritional levels can control protein synthesis rates not only in muscle but also in the liver and gill. 

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