Evaluation of equilibrium gel filtration chromatography for the study of protein binding of aluminum in normal and uremic sera

Normal and uremic serum samples were chromatographed on a gel filtration column and fractions were analyzed for protein and aluminum content. Whereas much of the aluminum in the serum samples eluted with protein, a significant fraction appeared to be associated with low molecular weight species. Analysis of column fractions for aluminum binding by a competitive binding assay indicated no aluminum-binding serum constituents in these later eluting fractions. Uremic serum appeared, however, to contain aluminum-binding constituents of a lower molecular weight than in normal serum.     

Aluminum deposition in the central nervous system. Preferential accumulation in the hippocampus in weanling rats

Simultaneous administration of 1,25-dihydroxyvitamin-D3, citrate, and aluminum-containing phosphate binders is frequently used in patients with chronic renal failure. In order to investigate whether citrate may represent a risk factor of aluminum intoxication, 16 Sprague-Dawley weanling rats were randomly assigned to four groups: 1,25-dihydroxyvitamin-D3 at 16 ng/kg/day was given to all groups except the control; in addition, two groups received either aluminum hydroxide at 160 mg elemental aluminum/kg/day, or aluminum citrate at 160 mg elemental aluminum/kg/day, respectively. The control group received only the vehicle. Extremely high aluminum concentrations were detected in the hippocampus of rats receiving aluminum compounds. This content of aluminum (microgram/g dry weight) was far higher than that found in other brain areas of the same animals (146.40 +/- 51.23 versus 4.49 +/- 0.62, P less than 0.001) as well as that detected in the hippocampus of the control animals (2.73 +/- 0.40). Thus, in non-uremic, weanling rats supplemented with 1,25-dihydroxyvitamin-D3, the administration of aluminum favors selective accumulation in the hippocampus. No differences between aluminum hydroxide and aluminum citrate administration were observed.     

Limitation of deuterium labelled methoximes as internal standards in the mass spectral analysis of prostaglandins

A reported method for the preparation of d₃-methoxime derivatives as internal standards for prostaglandin assays by gas chromatography-mass spectrometry was evaluated. Sample derivatization resulted in 1.5–86 % exchange of the d₃ -methoxime in a series of prostaglandins. Exchange was minimal when the methoxime was on the 5-membered ring; whereas, acyclic methoximes exhibited extensive exchange. Induced strain energy due to the steric interaction of the hydroxyl group and the C₁₃-C₂₀ alkyl side chain with the gem-dimethoxylamine transition state is offered as an explanation for the unusual stability of PGE₂. The use of ¹⁸O exchange of the carboxylic acid function is presented as an alternative for the preparation of unavailable labelled eicosanoids.     

Use of serine-protease inhibitors as probes for the different proteolytic activities of the rat liver multicatalytic proteinase complex.

The multicatalytic proteinase (MCP) complex catalyses cleavage of bonds on the carboxy-group side of basic, hydrophobic or acidic amino acid residues. Originally, it was proposed that the complex contained three distinct types of catalytic component. MCP from rat liver has been assayed for so-called trypsin-like activity with Boc-Leu-Ser-Thr-Arg-NH-Mec (Mec, 4-methylcoumarin; Boc, t-butoxycarbonyl), for chymotrypsin-like activity with Ala-Ala-Phe-NH-Mec and Suc-Leu-Leu-Val-Tyr-NH-MEc (Suc, succinyl), and peptidyl-glutamylpeptide hydrolase activity with Cbz-Leu-Leu-Glu-Nap (Nap, naphthylamide; Cbz, benzyloxycarbonyl). Results of these studies suggest that as many as five distinct components can be distinguished, one for the trypsin-like activity and two for each of the others. The activities were tested with a variety of serine-protease inhibitors, and other novel effectors have also been identified. The two most effective inhibitors were 4-(2-amino-ethyl)benzenesulphonyl fluoride, which selectivity inactivates the trypsin-like activity, and 3,4-dichloroisocoumarin which inhibits chymotrypsin-like activity and the second, cooperative component [Djaballah, H. & Rivett, A. J. (1992) Biochemistry 31, 4133-4141] of peptidylglutamylpeptide hydrolase activity. The three activities inhibited by 3,4-dichloroisocoumarin can easily be distinguished by the effects of chymostatin analogues, diisopropylfluorophosphate, guanidine/HCl and casein. The results support the view that the enzyme is a novel type of serine protease and suggest that it may contain at least five distinct catalytic components. Marked differences in the reactivities of the different catalytic sites with different reagents can be used to distinguish between them.     

Meal occurrence in Japanese quail in relation to particle size and nutrient density

Japanese quail ate shorter meals with pellets than with mash, and longer and more frequent meals with diluted mash (40% cellulose) than undiluted mash. The differences with particle size were due to different rates of ingestion, and those with nutrient density to different meal volumes and different rates of passage. Average meal size was about the same with all foods in terms of weight eaten, but not nutrients digested. Short-term adjustments in feeding were concerned mainly with changes in meal frequency, and longer-term adjustments mainly with changes in meal size. It is concluded that the control of meal-eating is concerned with emptying and filling of the digestive tract and not with changing levels of circulating nutrients, and parts of the gut that may be involved are suggested.     

Chemical composition of caecal contents in the fowl in relation to dietary fibre level and time of day.

1. Immature hens were preconditioned to a standard diet containing either 0, 100, 200 or 400 g/kg of added dried grass, 200 g/kg powdered cellulose, or 200 g/kg grass with an enzyme supplement, and were killed at either 10.30, 12.30 or 15.30 hr (after measurement of intestinal sugar absorption reported elsewhere). 2. Contents of caeca removed from these birds immediately after death were weighed and analysed for pH, uric acid, free sugars and volatile fatty acids, and the results related to dietary fibre level and time of day (of death). 3. Wet weights and uric acid concentrations of caecal contents both increased with increasing grass in the diet; neither measure varied with time, thus supporting the proposal that filling of caeca is continuous. Values of pH were all close to neutrality. 4. Mean molar concentrations of glucose, galactose, mannose, xylose, arabinose, fucose and rhamnose were in the proportions 36:2:3:1:4:1:1, respectively. Xylose and rhamnose declined with increasing grass; as did glucose, galactose and mannose with added cellulose; glucose, mannose and arabinose levels changed with time. The relative abundance of glucose in caecal contents should be taken into account when estimating contributions of fermentation products to energy balance. 5. Mean concentrations of acetate, propionate, butyrate, iso-butyrate, valerate and iso-valerate were in the proportions 72:22:16:1:2:2. Acetate declined and iso-valerate increased with increasing grass; the cellulose and enzyme treatments caused increases in acetate and valerate respectively; butyrate, iso-butyrate and iso-valerate levels changed with time.     

Investigations into the effects of processing on the retention of the carotenoid fractions of Leucaena leucocephala during storage,and the effects of processing on mimosine concentration

Leucaena leucocephala leaves were subjected to several drying treatments followed by pelleting and/or inclusion of ethoxyquin as antioxidant and analysed monthly to determine rates of loss of carotenes and xanthophylls. Rapid sun drying yielded leucaena leaf meal with carotene and xanthophyll concentrations of 446 and 865 mg/kg, respectively, but considerable losses occurred during drying at 60 and 145°C, and as a result of blanching in hot water or ferrous sulphate solution. Loss rates of carotenes during storage were in the range 19–40 mg/kg per month, and of xanthophylls, 29–53 mg/kg per month. Carotenoids in sun-dried leaf meal were most stable during storage. Pelleting or inclusion of ethoxyquin did not reduce carotenoid loss rates below those of unpelleted leaf meal.The mimosine content of untreated sun-dried leucaena leaf meal was 3.2%, but the concentration decreased to 2.5 and 1.8% on drying at 60 and 145°C, respectively. The concentrations of mimosine in sun-dried leafmeals of water-blanched and ferrous sulphate-blanched leucaena were 2.0 and 2.1%, respectively. Treatments causing maximum losses of mimosine were those which brought about maximum losses of carotenoids.