Norlin J. Benevenga

Role of protein synthesis in amino acid catabolism

Except for branched chain amino acids, the site of indispensable amino acid degradation is the liver. Location of amino acid degradation capacity in a single organ may play an important role in the reutilization of amino acids derived from protein turnover. The importance of preferential utilization of amino acids for protein synthesis on catabolism of amino acids is demonstrated in two ways. First, by minimal oxidation of an amino acid at dietary concentrations below that required for maximum gain followed by a near proportionate oxidation with increased dietary level, and second, by increased oxidation of an indispensable amino acid when another amino acid limits protein synthesis. A direct effect of protein synthesis on amino acid catabolism can be shown by a marked increase in amino acid catabolism when protein synthesis is inhibited.

Effects of cereals and culture filtrate ofTrichoderma viride on lipid metabolism of swine

Swine were fed corn-or barley-based diets with, or without, culture filtrate (CF) ofTrichoderma viride for 21 days. Weight gains were nonsignificantly but slightly increased by CF. The activities of β-hydroxy-β-methylglutaryl coenzyme A (HMG-CoA) reductase, cholesterol 7α-hydroxylase, acetyl-CoA carboxylase (ACX), fatty acid synthetase (FAS) and other lipogenic enzymes in several tissues were determined. Significant decreases in the activities of HMG-CoA reductase and cholesterol 7α-hydroxylase in all tissues of swine fed the CF-diets were observed. The major site for the regulation of cholesterol biosynthesis was adipose tissue followed by the intestine, liver, lung and muscle in order of activity The concentrations of cholesterol in serum and muscle were decreased 27% and 23%, respectively, by CF. ACX and FAS activities increased ca. 2-fold when CF was fed with either of the cereal-based diets. The major sites for fatty acid synthesis was the adipose tissue and, to a lesser extent, the liver. Very low rates of synthesis were detected in intestine, lung and muscle. Similar distributions of activities were found for related lipogenic enzymes.

Unique Aspects of Lysine Nutrition and Metabolism

Lysine nutrition is unique among indispensable amino acids in that it can be conserved and can be fed 12 h out of phase (delayed supplement) with the other dietary amino acids. In piglets, high levels (2-6%) of L-lysine added to a 10% protein diet can be tolerated without obvious detrimental effects. In both rat and piglet liver preparations, the first enzyme in the saccharopine-dependent pathway of lysine catabolism, lysine alpha-ketoglutarate reductase (LKR), is found only in the mitochondrial matrix. For Lys catabolism to occur, Lys must first enter the matrix of the mitochondrion. LKR, saccharopine dehydrogenase, mitochondrial lysine uptake, and lysine oxidation (LOX) all increased>3-fold in rats fed high levels of dietary protein (up to 60%). The activities of mitochondrial Lys uptake and LOX were similar when expressed as mmol/(d.100 g body weight). Thus, LOX can be a proxy for mitochondrial Lys uptake. Piglet liver LKR and LOX increase 5- to 10-fold when piglets are fed high-protein (50 or 75%) diets. In both the rat and piglet, after adapting to the high protein diet, the activity of LKR is 400-500 times that of LOX, suggesting that Lys uptake by a transporter(s) is rate limiting. Quantitative 24-h dietary infusion studies in piglets revealed that>80% of the Lys infused (4% of the diet) could not be recovered in the urine or body or accounted for by calculated Lys oxidation based on liver activity of LOX. Other pathways and tissues may account for the Lys oxidation in piglets.

The influence of dietary unsaturated cis and trans and saturated fatty acids on tissue lipids of swine

A feeding trial was conducted to evaluate the effects of dietary trans unsaturated fatty acids (trans fat) and of the interplay of dietary saturated fatty acids (saturated fat), cis unsaturated fatty acids, (cis fat) and trans fat on tissue lipids, particularly those effects suggestive of angiotoxicity. Swine were fed for 10 months a diet containing 17% added fat. Seven blends of varying proportions of the 3 fat components provided sufficient sample points to permit an examination of the interplay. Parameters under study included weight gain, serum cholesterol and triglyceride concentrations, lipoprotein lipid profile, total lipid and cholesterol concentrations of liver, heart and aorta, fatty acid composition of liver and aorta lipids and hepatic fatty acid synthesis and cholesterol synthesis and oxidation. Fat blends containing disproportionately high levels of saturated or cis fat generally elicited responses consistent with results reported by others. The notable exception was the serum cholesterol concentration. Throughout the study, the swine were hypercholesterolemic. Swine fed the high saturated fat blend had serum cholesterol levels equal to those swine fed the high cis fat blend. Serum cholesterol levels in the swine fed the other fat blends were more elevated. Another apparent anomaly was the lower concentration of lipid in the aortas of swine fed the high-saturated fat diet. The impact of the trans fat was modulated by the relative proportions of saturated and cis fat in the diet. The impact of trans fat was of greater magnitude for most parameters when the fat blend was low in saturated fat. The sole parameter suggestive of trans fat-mediated angiotoxicity was the distribution of lipids in lipoprotein fractions. Swine fed diets containing trans fat had lower relative proportions of the alpha-lipoprotein lipids. Although hypercholesterolemic, the high fat diets were not overtly angiotoxic except when fed to swine that carried a specific immunogenetically-defined low density lipoprotein.

Estimate of fatty acid turnover in porcine adipose tissue

Fatty acid turnover in the domestic pig was estimated by measuring the half-life of linolenic acid depletion in adipose tissue depots which had been made abnormally high in linolenic acid by feeding large quantities of linseed oil. The measured half-life of linolenate in 8- to 12-month-old pigs was 300 days. The apparent half-life of linolenate in muscle lipids was less than that of subcutaneous backfat.

The decarboxylation of α-keto-γ-methiolbutyrate in rat liver mitochondria

Abstract The decarboxylation of α-keto-γ-methiolbutyrate, the α-keto acid of methionine has been studied in rat liver. Most (70%) of the decarboxylation activity is in the mitochondrial fraction. The Km for the decarboxylation of α-keto-γ-methiolbutyrate in intact mitochondria is 0.6 mM. Pyruvate, α-keto-butyrate and α-ketoisocaproate significantly inhibit this activity. The inhibition due to α-ketoisocaproate is 3.3 fold that of pyruvate and 1.1 fold that of α-ketobutyrate at a concentration of 0.4 mM.

Variations in the recovery of carbon-14 in colored samples treated with peroxide

Abstract Treatment of colored samples with peroxide resulted in a loss of carbon-14. The proportion of counts lost varied in different biological samples even though the tracer was the same. Treatment of different amino acids with peroxide resulted in wide variations in their destruction. The results showed that the routine use of peroxide to decolorize samples may have serious drawbacks.

The evaluation of fresh sweet liquid whey as a protein supplement to maize for growing pigs

Abstract Whey protein, provided by liquid cheddar cheese whey, or a dried protein concentrate was evaluated as a protein supplement to maize-based diets for growing—finishing pigs. In Trials 1 and 2, pigs received either water or fresh liquid whey with a maize-based dry diet, to provide three levels of total dietary crude protein (CP). Liquid whey maintained growth rates at the level of pigs receiving the highest CP level and water, despite a reduction in CP intake of 33%. Liquid consumption by pigs given fresh cheddar whey was 2–3 times that of pigs given water. Whey solids supplied 24.0–58.5% of the total dry matter (DM) consumed by growing—finishing pigs. In Trial 2, pigs given maize supplemented only with vitamins, minerals and fresh cheddar cheese whey ad libitum grew as well as pigs fed on a maize and soya bean meal diet containing 18.1% CP. In Trial 3, dried whey was compared to soya bean meal as a supplement to maize protein, when both provided 50% of the total protein. The daily gain with whey protein as the supplement was 1.36 times that when soya protein was used. Whey protein is shown to be superior to soya as a supplement to maize. Although the dry matter (6%) and protein (0.8%) of liquid whey is low, a high voluntary consumption by pigs make it a good protein supplement in maize-based diets.

The synthesis of radioactive 3-methylthiopropionate and other alkylthio fatty acids.

Abstract Aprocedure is described for the synthesis of radioactive 3-methylthiopropionate, a recently isolated metabolite of mammalian methionine metabolism. The method is a two-step synthesis whereby correspondingly labeled methionine is degraded by ninhydrin to 3-methylthiopropionaldehyde and then specifically oxidized to 3-methylthiopropionate without oxidation of the sulfur atom by the yeast enzyme, aldehyde dehydrogenase. Radiochemical purity of the isolated product was established by paper, thin-layer, and gas-liquid chromatography. This procedure is economical and readily applicable to the synthesis of other alkylthio fatty acids for the study of S -methylcysteine and ethionine metabolism and probably for the synthesis of radioactive intermediates of branched chain amino acids.

Octanoate and Nonaoate Oxidation Increases 50–80% Over the First Two Days of Life in Piglet Triceps Brachii and Gracilis Muscle Strips

An in vitro muscle strip incubation system was developed to measure the rate of catabolism of 1 mmol/L [1-(14)C]octanoate, 1 mmol/L [1-(14)C]nonanoate, 1 mmol/L [9-(14)C]nonanoate, and 10 mmol/L [U-(14)C]glucose by measuring the recovery of (14)CO(2). Muscle strips (13 mm × 1.5 mm, ~50 mg) were isolated from triceps brachii and gracilis muscles of newborn and 2-d-old, small (<950 g) and large (>1450 g) piglets. The position of the (14)C label in the substrate affected the rate and amount of recovery in (14)CO(2). Therefore, comparisons were made between age groups (0 vs. 2 d old) within substrates but limited across substrates to comparisons of [1-(14)C]-labeled fatty acids. The medium-chain fatty acid (MCFA) oxidation rates [pmol/(h · mg)] in muscle strips isolated from piglets from the 2 weight groups (<950 and >1450 g) did not differ (P > 0.99), there was a trend towards a difference between triceps brachii and gracilis muscle (P = 0.09; data not shown), and there were no significant interactions involving pig weight or muscle type; therefore, results were pooled across these factors. During the first 2 d of life, MCFA oxidation [pmol/(h • · mg muscle strip)] increased (P < 0.05) 50-80%, but the glucose oxidation rate did not change (P > 0.82). By d 2, the oxidation rate of nonanoate as represented by the one carbon was 25% greater than for octanoate (P < 0.05). The conversion of [9-(14)C]nonanoate to (14)CO(2) indicated that muscle had the capacity to oxidize the propionyl-CoA produced by β-oxidation of nonanoate and that odd-chain C-9 MCFA provided anabolic carbon to the citric acid cycle.