Metabolism of (3-(14)C)tryptophan and (2-(14)C)alanine in cattle tissues

In the experiments involving incubation of the liver, brain cortex, muscle and adipose tissues homogenates with [3-14C] tryptophan for an hour 43.2-89.3% of the label was found in proteins, 7.2-47.2%--in lipids, 2.6-9.4%--in CO2. Following incubation of the above-mentioned tissue homogenates with [2-14C] alanine, proteins, lipids and CO2 contain 28.8-49.3%; 22.6-31.9% and 21.6-49.3% of radioactive label, respectively. Radioactivity of lipids synthesized by the homogenates of the investigated tissues from [3-14C] tryptophan and [2-14C] alanine is 23.5-63.5 and 21.1-56.0%, respectively, the radioactivity of CO2 being 1.4-5.1 and 9.3-11.8% of the above-mentioned compounds synthesized from [1-14C] acetate. The results obtained testify to the considerable contribution of [3-14C] tryptophan and [2-14C] alanine to protein synthesis as well as to their involvement in the substrate supply of lipogenesis and energetic processes in various organs and tissues of cattle.     

Effect of insulin and cortisol on oxidation of (1-14C)glucose, (6-14C)glucose, (1-14C)palmitate and (1-14C)leucine in the tissues of swine during the neonatal period

The intensity of [1-14C]glucose, [6-14C]glucose, [1-14C]palmitate and [1-14C]leucine oxidation and the effect of insulin and hydrocortisone on this process were studied in the brain, duodenum mucosa, liver and skeletal muscle of 1- and 5-day old piglets in vitro. Most of the studied substrates are oxidized in the tissues of 5-day piglets more intensively. Insulin stimulates oxidation of [1-14C]glucose, [6-14C]glucose and [1-14C]leucine in the brain and duodenum mucosa in 1- and 5-day old piglets, while in the liver and skeletal muscle--only in 5-day old piglets. Hydrocortisone administration enhances oxidation of [1-14C]leucine in most of the studied tissues in 1-day piglets and oxidation of [1-14C]glucose and [6-14C]glucose--in 5-day piglets. Both hormones produce no essential influence on the intensity of [1-14C]palmitate oxidation in the studied tissues of piglets or somewhat weaken it.     

Hydrolysis of glyceryl tri(1- 14 C)octanoate and glyceryl tri(1- 14 C)oleate monolayers by postheparin lipolytic activity

The hydrolysis of monomolecular films of glyceryl tri[1-(14)C]octanoate and glyceryl tri[1-(14)C]oleate has been demonstrated by measurement of the decrease in surface radio-activity that occurs in the presence of postheparin plasma. The hydrolysis displayed first order kinetics and was proportional to enzyme concentration over a 10-fold range. No hydrolysis was observed in the absence of enzyme, and only slight activity (1%) was found in plasma taken from subjects before heparin administration. The hydrolysis was stimulated to a variable extent by Ca(2+). The first product of hydrolysis of the monolayer was identified as 1,2-diglyceride, which was subsequently converted to 2-monoglyceride. Inhibition of triglyceride hydrolysis was observed when postheparin plasma was preincubated in 2 m NaCl, 10(-4) m protamine, 10 mm Na(4)P(2)O(7), and 0.1 m NaF. Monolayer techniques avoid some but not all of the problems associated with emulsified lipid substrates and appear to be applicable for study of post-heparin lipolytic activities.     

Conversion of (U-14C)-glycerol, (2-3H)-glycerol and (1-14C)-palmitate into circulating lipoproteins in the rat.

The in vivo formation of labelled very low density lipoproteins (VLDL) from (U-14C)-glycerol, (2-3H)-glycerol and (1-14C)-palmitate was studied in fed female rats. The rate of disappearance of radioactivity from plasma after the i.v. injection with these tracers was similar for (U-14C)-glycerol and (1-14C)-palmitate. With (2-3H)-glycerol, plasma radioactivity at 10 min was lower than with the other substrates although it did not change thereafter. A certain proportion of radioactivity administered as glycerol appeared in plasma lipids, mainly in the VLDL glyceride glycerol fraction, although when (U-14C)-glycerol was the substrate, a considerable portion also appeared in the esterified fatty acids of these lipoproteins. When using (1-14C)-palmitate, practically all the circulating labelled esterified fatty acids appeared in the VLDL fraction, while the labelled free fatty acids appeared in lipoprotein of higher density, presumable free fatty acid-albumin complexes. This data is discussed in terms of the role of the liver in the rapid, continuous cycling of these substrates to yield VLDL-glycerides for their extrahepatic utilization.     

Preparation and Metabolism of 2-(14C)-cis, trans-Xanthoxin

2-[¹⁴C]-cis, trans-xanthoxin (specific activity 0.26 µCi/µmol)has been synthesized from4-(1', 2'-epoxy-4'-hydroxy-2', 6',6'-trimethyl-l'-cyclohexyl)-trans-3-buten-2-oneand methyl 2-[¹⁴C]-bromoacetate. When 2-[¹⁴C]-cis, trans-xanthoxin was fed to cut shoots of tomatoand dwarf bean, it was converted within 8 h to (+)-abscisicacid in yields of 10.8 and 7.0 per cent respectively. Pea seedsand tomato fruits gave much smaller conversions. A second majormetabolic product extracted from treated tomato and bean shootswas shown to be a metabolite of abscisic acid and has been tentativelyidentified as phaseic acid. These results, together with the earlier finding that xanthoxinis present in the extracts of many seedlings, suggest that xanthophyllsand xanthoxin may be precursors in the biosynthesis of ( + )-abscisicacid