Differences In Protein Metabolism Research Articles

Early curbing of protein hypercatabolism in postoperative patients by nutritional support with glucose plus amino acids, but not with glucose alone

This work attempts to determine if there are differences in protein metabolism in post-surgical patients who receive parenteral nutrition with amino acids plus glucose (G+AA) or conventional gluco-salinal solution (GS). Eighteen patients submitted to gastrointestinal surgery were randomized and double-blindly administered either G+AA (1 g AA/kg.d and 28 kJ/kg.d), or GS (28 kJ/kg.d). Protein metabolism was determined 12 h after surgery (day 0) and after 5 days of nutritional support. On day 0, protein breakdown was simillarly elevated, with respect to reference values, in both groups (GS: 4.62 ± 0.25; G+AA: 5.25 ± 0.50 g prot/kg.d) as a result of surgical stress. These values increased significantly at day 5 ( P < 0.03) with the administration of GS to 6.93 ± 1.00 g prot/kg.d, while they decreased ( P < 0.002, 3.30 ± 0.42 g prot/kg.d) with G+AA. Protein synthesis was increased (5.69 ± 0.86 g prot/kg.d) with GS ( P < 0.02), and was decreased (2.79 ± 0.44 g prot/kg.d) with G+AA ( P < 0.0002). Both synthesis and breakdown were inside normal reference values after 5 days for group G+AA. In both groups, nitrogen balance did not change significantly at day 5 compared to day 0. G+AA is effective in curbing the hypermetabolism produced by postoperative stress, achieving normal protein metabolism in 5 days, while GS increases the protein breakdown and synthesis. Nitrogen balance does not detect these modifications of the protein metabolism. Undernutrition on prognosis is not yet fully recognized.

The metabolic basis of genetic differences in growth efficiency among marine animals

This paper initially reviews evidence for genetic influences upon growth efficiency. We then discuss recent advances in our understanding of the metabolic links whereby genotype affects whole-animal physiology and growth efficiency through differences in protein metabolism. Most evidently, these differences are in protein turnover, defined as the continuous breakdown and replacement of cellular proteins and which provides the flux that is necessary for metabolic regulation and adaptation. Whether comparing individuals, including associations with genetic heterozygosity, or considering the response to breeding, selection or genetic manipulation, reduced whole-body protein turnover consistently underlies lower energy expenditure and higher growth efficiencies. The present paper describes results from our recent studies that have explored the metabolic basis and functional consequences of these differences in whole-body protein turnover by comparing the component activities of specific proteolytic pathways in the mussel Mytilus edulis. Traditionally, it has been thought that requirements for biosynthesis dominate energy expenditure. Nevertheless, a large component of about 30% of the empirical costs of protein deposition cannot be attributed to known synthetic processes and it has been suggested that costs of protein turnover may contribute to the discrepancy. Findings are presented showing that separate whole-body activities of the four main lysosomal proteases were collectively associated with as much as 73% of the variation in maintenance energy expenditure observed between individual mussels. These associations were positive for cathepsin B, cathepsin D and leucine aminopeptidase ( Lap-2). Alternatively, higher whole-body activity of cathepsin L was associated with lower maintenance energy expenditure, possibly because cathepsin L was most active in the main tissue of nutrient storage, thereby mobilising energy reserves and reducing the need for protein turnover in remaining tissues. Results therefore indicate profound physiological consequences of lysosomal proteolysis under conditions of partial starvation, but which vary according to functional differences between separate proteolytic pathways. These findings establish that the relative balance between proteolytic pathways is central to our understanding of different efficiencie 12989as in energy requirements and conversion efficiency.

Individual variation in protein turnover and growth efficiency in rainbow trout, Oncorhynchus mykiss (Walbaum)

The aims of this study were to examine the relation between consumption, growth and protein synthesis for individual rainbow trout held in groups, and to examine how differences in protein turnover may help to explain the observed differences in protein growth rate between rainbow trout with similar protein consumption rates. Therefore four measurements of consumption were made for 37 individual fish over a 73 day period by using radiography. At the end of the experiment, fractional rates of protein synthesis were measured by using a single flooding dose injection of [$^{3}$H]phenylalanine. The results showed that fractional rates of protein growth and synthesis increased with consumption rate. However, degradation rates were independent of consumption. Fish consuming similar amounts of food exhibited two- to threefold differences in fractional protein growth rates, and twofold differences in fractional rates of protein synthesis. Nine pairs of fish with similar protein consumption rates but different rates of protein growth were selected to examine if differences in protein metabolism, digestive efficiency or RNA concentration or activity could explain these observed differences in protein growth efficiency. More efficient fish were found to have reduced degradation rates; this was the only significant result obtained. The results support the hypothesis that individual differences in protein turnover are important determinants of growth efficiency in fish.

Behavior of L-threonine-degrading enzymes during liver regeneration.

We examined the effects of a two-thirds hepatectomy in the adult rat on the activities of the three L-threonine-degrading enzymes, L-threonine dehydratase, L-threonine aldolase and L-threonine dehydrogenase. Noticeable variations were observed which did not occur in either sham-operated or turpentine-treated rats and were not linked to food intake. They were considered specific to the regenerating liver. When the reactions were followed in vitro, L-threonine deaminase and L-threonine aldolase were significantly lower for the first 12-24 h: L-threonine dehydrogenase decreased only after 48 h. These results are linked to a decrease in the enzyme concentration in the tissue. L-Serine and L-threonine liver concentrations increased 2-3-fold during the same periods. When the activities were evaluated in vivo, the levels of the first two enzymes remained constant for 24 h, but increased after 48 h; L-threonine dehydrogenase increased between 12 and 48 h. The in vivo activity of the enzymes was reflected by total L-threonine degradation, which had a single sharp peak at 48 h. The asynchronous variations in enzyme activity are related to the differences in protein metabolism which occur in the regenerating liver, and are the consequence of a new transient differential control. The changes observed are significant in liver regeneration; they regulate the consumption and the serum and liver levels of L-serine and L-threonine, setting them aside for protein synthesis. They minutely control the flux of amino acids toward gluconeogenesis, since, during the first 48 h after partial hepatectomy, the production of glucose is ensured principally by lactate; the contribution of L-threonine seems to be more significant only at 48 h. These findings are useful in the study of the regulation of the enzymes involved in amino acid metabolism during liver regeneration.

26. PROTEIN METABOLISM IN VERY-LOW-BIRTH-WEIGHT (VLBW) INFANTS SMALL FOR GESTATIONAL AGE (SGA) FED PROTEIN FORTIFIED HUMAN MILK (HM)

In order to demonstrate metabolic differences in response to protein intake we have studied 23 AGA and 19 SGA infants of VLBW at the eight day of life. The infants received HM or HM fortified with HM-lyophilisate at protein intakes ranging from 2.0 to 3.5 g/kg/d as calculated from protein content of the milk and the volumes ingested. α-amino-nitrogen and amino acids in serum as well as total nitrogen and α-amino-nitrogen excretion in the urine was measured. Serum α-amino-nitrogen and amino acid concentrations correlated with protein intake in both groups of infants, but concentrations were significantly higher in the SGA-infants above a protein intake of 2.5 g/kg/d. α-amino-nitrogen and total nitrogen excretions in the urine reflected also protein intake and were significantly increased in the SGA-infants. On the eight day of life a protein intake above 2.5 g/kg/d produces metabolic indices of protein overload in SGA-infants. These findings demonstrate that differences in protein metabolism are present between AGA and SGA infants of VLBW. A decreased rate of protein utilization for some time after birth may be present in the SGA-infants. When the nutritional management of VLBW-infants is planned these differences must be considered and protein intakes should be increased with caution in the SGA-infants.

Thermal Responses Reflect Protein Turnover in Mytilus edulis L.

Relationships between whole-body protein turnover and energy metabolism are defined from studies of 15 individual Mytilus edulis L. Differences in protein metabolism are shown to affect growth rate, temperature sensitivity of metabolic rate, rate of thermal acclimation and ability to survive high temperatures. Faster growth in individuals fully acclimated at 100C derived primarily from reduced metabolic requirements associated with lower intensities of protein turnover. Protein turnover may also have amplified metabolic responses upon transfer of mussels from 10 to 200G, for accompanying increments of both protein synthesis and oxygen uptake were proportionally higher among slower-growing individuals. These same individuals subsequently implemented the greatest daily savings in energy expenditure, so that complete thermal acclimation had been effected within 14 days. Slow-growing mussels with the fastest intensities of protein turnover at 100C were also the first to die following a further increase from 20 to 28 5 G. This reflected their greater temperature sensitivity; elevated metabolic demands apparently exceeding a critical threshold. We suggest that these differences are genotype-dependent but emphasize that relative fitness advantages of differential protein turnover may vary according to specific circum-

Tissue and whole-body protein synthesis in immature Zucker rats and their relationship to protein deposition.

The rates of protein synthesis in skeletal muscle, intestine, liver and in the whole body of immature (18 and 25 days old) lean and obese male Zucker rats were measured. In addition, the rate of deposition of whole-body and skeletal-muscle protein over the period 16-27 days post partum was measured by comparative slaughter and analysis of the composition of the body. At 16 days post partum, lean and obese rats had similar body protein contents, but thereafter the rate of protein deposition in the body and skeletal-muscle mass was decreased in the obese rats. The decrease was particularly marked before 21 days of age, and between 23 and 27 days post partum the fractional rate of protein deposition was the same in lean and obese rats. Of the tissues that were studied, only skeletal muscle had a lower fractional rate of protein synthesis in the obese rats. At 18 days post partum, the decrease in the absolute rate of protein synthesis in skeletal muscle accounted for at least 80% of the decline in protein synthesis in the whole body. After weaning, phenotypic differences in protein synthesis was less marked than at 18 days of age, and skeletal muscle accounted for only 50% of the difference in body protein synthesis between phenotypes. The possibility that a change in the function of the adrenal cortex contributes to differences in protein metabolism between lean and obese Zucker rats is discussed.

Effect of training on muscle protein turnover in male and female rats

These experiments were undertaken in order to investigate the changes in protein synthesis and degradation which result from physical training in male and female rats. Protein synthesis and protein degradation were measured in perfused hemicorpus preparations from trained and untrained male and female rats. Additionally, the activities of several muscle proteinases were measured. The rates of protein synthesis and degradation were greater in females than in males. Protein degradation was increased by training in males but not in females. There were no changes in protein synthesis rates due to training in either sex. Myofibrillar alkaline proteinase was observed to be more active in females than in males, but there were no changes in levels of muscle proteinases as the result of training. Since we observed that exercise training resulted in a decreased rate of weight gain in male rats but not in female rats, it seems that the differences in protein metabolism observed between males and females contribute to the difference in growth rate response to endurance training.

In vitro protein synthesis with polysomes from unpollinated, cross- and self-pollinated Petunia ovaries

From in-vitro protein synthesis studies it has been shown that in Petunia hybrida (clone W166K, incompatibility genes S1S2) the ovary is stimulated to synthesize proteins before the pollentubes reach the ovary. A difference in protein metabolism is detected after self- and cross-pollination. On the basis of this result has been concluded that a signal has to be sent from the stigma or the style towards the ovary which induces the changes in metabolic activity. The signal must be different for cross- and self-pollination.

Metabolism of nuclear and cytoplasmic proteins in the visual cortex of sighted rats and rats with retinal degeneration

The protein metabolism in the visual cortex of visually stimulated adult blind and sighted rats has been compared using intraperitoneally administered radioactive leucine. The blind rats belonged to a strain suffering from an inherited retinal dystrophy which renders them blind within 3–4 weeks of birth. A reduced incorporation of l-[1- 14C]-leucine into both nuclear and cytoplasmic proteins was observed in the visual cortex of the blind animals. This could not be attributed to a reduced rate of transport of leucine from the site of injection to the visual cortex. On fractionating the nuclear proteins, the largest differences were found in the residual protein fraction and the buffered saline-soluble fraction (both believed to be associated with the nucleolus). There was no significant difference in the acid chromatin and histone fractions. The differences in protein metabolism in the visual cortex were not seen in the frontal cortex.

Protein synthesis in leukocytes of diabetic and normal subjects.

THERE are some indications that diabetes mellitus is a disease involving a disorder of carbohydrate, lipid and protein metabolism. Leucocytes possess a nucleus and mitochondria, and metabolize glucose, amino-acids and fatty acids, and therefore might be useful for the investigation of certain aspects of metabolism in human diabetes. Investigation of glucose uptake and oxidation, lipid metabolism and lactic acid formation in leucocytes has had varied results1–3. Protein synthesis has not been investigated in leucocytes, and we aimed to determine the differences in protein metabolism in leucocytes from control and diabetic patients.

Plasma Amino Acids in Young and Older Adult Human Subjects

Abstract Nineteen amino acids were determined in the plasma of young and older individuals by the chromatographic procedure of Moore, Spackman, and Stein (7,8). Of the essential amino acids, valine, methionine, isoleucine, leucine, phenylalanine, and lysine were found to be lower in older subjects. In all, 11 of the 19 amino acids studied showed lower values in these individuals, indicating some differences in protein metabolism between the elderly and younger adults.