Branched-chain amino acids and muscle protein synthesis in humans: ..

This pool is regenerated by dietary proteins and tissue protein degradation and is the source of protein synthesis as well as nitrogen secretion while maintaining nitrogen level homeostasis.

T1 - In vivo measurement of synthesis rate of multiple plasma proteins in humans

AB - Nonselective blockade of the cyclooxygenase (COX) enzymes in skeletal muscle eliminates the normal increase in muscle protein synthesis following resistance exercise. The current study tested the hypothesis that this COX-mediated increase in postexercise muscle protein synthesis is regulated specifically by the COX-2 isoform. Sixteen males (23 ± 1 yr) were randomly assigned to one of two groups that received three doses of either a selective COX-2 inhibitor (celecoxib; 200 mg/dose, 600 mg total) or a placebo in double-blind fashion during the 24 h following a single bout of knee extensor resistance exercise. At rest and 24 h postexercise, skeletal muscle protein fractional synthesis rate (FSR) was measured using a primed constant infusion of [2H5]phenylalanine coupled with muscle biopsies of the vastus lateralis, and measurements were made of mRNA and protein expression of COX-1 and COX-2. Mixed muscle protein FSR in response to exercise (P 0.05) between the placebo and COX-2 inhibitor postexercise when controlling for resting FSR. The COX-2 inhibitor did not influence COX-1 mRNA, COX-1 protein, or COX-2 protein levels, whereas it did increase (P

acids on muscle protein synthesis in humans and ..

The nitrogen balance is an indication of protein synthesis and degradation.

Carbohydrates. Human milk has a very high lactose content, 7 grams per deciliter or about 200 mM and lactose provides about 40% of the calories available to the infant. The adaptive significance of this high lactose content (the highest of any species currently known) is probably two-fold: (1) The infant brain is large and requires glucose as a metabolic substrate; lactose is broken down into glucose and galactose prior to intestinal absorption. (2) From an osmotic standpoint, the secretion of lactose obligates the concomitant secretion of a large amount of water. This water is sufficient to meet the infant's needs for sweating and transpirational water loss, high in a warm climate, as well as for urine formation. Because lactose can be synthesized only from glucose, maternal glucose utilization is increased by about 30% in the fully lactating woman.

results when the rate of muscle protein synthesis is ..

Human milk proteins. Human milk has a relatively low casein content compared with other mammals, approximately 0.2 g/dl in mature milk, probably reflecting the relatively slow growth rate of the human infant. Most of the casein in human milk is bound in micellar form. The casein micelle also contains most of the calcium and phosphate. The other major milk proteins that are synthesized in the mammary gland are -lactalbumin and lactoferrin, both are present at a concentration of about 0.2 g/dl in mature human milk. -Lactalbumin functions in the synthesis of lactose, the major carbohydrate in milk. Lactoferrin is an iron-binding protein found in high concentration in human colostrum and milk. It is considered to be a protective factor in milk because of its anti-bacterial properties. Only about 5-10% of its iron-binding capacity is occupied so that one mechanism of bacteriostasis is thought to be binding of iron needed by bacteria to multiply. Lactoferrin concentration in the mammary secretion is increased in colostrum, during mastitis, and following involution. The fourth major milk protein is secretory immunoglobulin A (sIgA), also present in mature milk at a concentration of about 0.2 g/dl. This protein is synthesized by cells of the immune system and transported into milk by a specific mechanism described below. It is also thought to act as a protective factor; its concentration is much higher in colostrum (up to 10 g/dl) and in post-involutional secretion than in mature milk. Other proteins in human milk include lysozyme (which has a particularly high activity in human milk), lipases, growth factors and many others.

Branched-chain amino acids and muscle protein synthesis …

Advances in quantitative proteomics have facilitated the measurement of large-scale protein quantification, which represents net changes in protein synthesis and breakdown. However, measuring the rate of protein synthesis is the only way to determine the translational rate of gene transcripts. Here, we report a technique to measure the rate of incorporation of amino acids from ingested protein labeled with stable isotope into individual plasma proteins. This approach involves three steps: 1) production of stable isotope-labeled milk whey protein, oral administration of this intrinsically labeled protein, and subsequent collection of blood samples; 2) fractionation of the plasma and separation of the individual plasma proteins by a combination of anion exchange high-pressure liquid chromatography and gel electrophoresis; and 3) identification of individual plasma proteins by tandem mass spectrometry and measurement of stable isotopic enrichment of these proteins by gas chromatography-mass spectrometry. This method allowed the measurement of the fractional synthesis rate (FSR) of 29 different plasma proteins by using the same precursor pool. We noted a 30-fold difference in FSR of different plasma proteins with a wide range of physiological functions. This approach offers a tremendous opportunity to study the regulation of plasma proteins in humans in many physiological and pathological states.