Does boron play only a structural role in the growing tissues of higher plants?

In species in which boron (B) mobility is limited, B deficiency only occurs in growing plant organs. As a consequence of the highly localized patterns of plant growth and the general immobility of B it has been extremely difficult to determine the primary function of B in plants. In species in which B is phloem mobile, the removal of B from the growth medium results in the depletion of B present in mature leaves. Thus, it is possible to develop mature leaves with increasingly severe levels of B depletion, thereby overcoming the complications of experiments based on growing tissues. Utilizing this approach we demonstrate here that B depletion of mature plum (Prunus salicina) leaves did not result in any discernible change in leaf appearance, membrane integrity or photosynthetic capacity even though B concentrations were reduced to 6-8 µg/g dwt, which is less than 30% of the reported tissue B requirement. Boron depletion, however, results in a severe disruption of plant growth and metabolism in young growing tissues. This experimental evidence and theoretical considerations suggest that the primary and possibly sole function of B, is as a structural component of growing tissues.     

Identification of porphyrin present in apo-cytochrome c oxidase of copper-deficient yeast cells

Heme a was not detected either in mitochondria isolated from copper-deficient yeast or in the intact cells. Nevertheless, the intracellular concentration of free porphyrins indicated that the pathway of porphyrin and heme synthesis was not impaired in copper-deficient cells. The immunoprecipitated apo-oxidase from copper-deficient cells revealed an absorption spectrum with maxima at 645, 592, 559, 519 and 423 nm, similar to that of purified porphyrin a. When solubilized mitochondria from [³H]leucine and δ-amino[¹⁴C]levulinic acid-labeled copper-deficient yeast cells were incubated with rabbit antiserum against cytochrome c oxidase, a precipitate was obtained. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of this immunoprecipitate showed [³H]leucine associated with six bands and δ-amino[¹⁴C]levulinic acid resolved in a single band. HCl fractionation of copper-deficient mitochondria labeled with δ-amino[¹⁴C]levulinic acid showed a high specific radioactivity in the fraction extracted by 20% HCl, a solvent which extracts porphyrin a. Thinlayer chromatography of the radioactivity found in 20% HCl showed an R_F value identical to that of purified porphyrin a. When δ-amino[³H]levulinic acid-labeled, copper-deficient yeast cells are grown in copper-supplemented medium, the porphyrin a accumulated in copper-deficient cells wa converted into heme a, and this conversion was prevented by cycloheximidine.These observations suggest that porphyrin a is present in the apo-oxidase of copper-deficient cells, but that the conversion to heme a does not occur. This conversion reaction appears to be a point in the biosynthetic pathway of cytochrome c oxidase which is blocked by copper deficieny.     

Plasma FA composition in familial LCAT deficiency indicates SOAT2-derived cholesteryl ester formation in humans

Mutations in the LCAT gene cause familial LCAT deficiency (Online Mendelian Inheritance in Man ID: #245900), a very rare metabolic disorder. LCAT is the only enzyme able to esterify cholesterol in plasma, whereas sterol O-acyltransferases 1 and 2 are the enzymes esterifying cellular cholesterol in cells. Despite the complete lack of LCAT activity, patients with familial LCAT deficiency exhibit circulating cholesteryl esters (CEs) in apoB-containing lipoproteins. To analyze the origin of these CEs, we investigated 24 carriers of LCAT deficiency in this observational study. We found that CE plasma levels were significantly reduced and highly variable among carriers of two mutant LCAT alleles (22.5 [4.0–37.8] mg/dl) and slightly reduced in heterozygotes (218 [153–234] mg/dl). FA distribution in CE (CEFA) was evaluated in whole plasma and VLDL in a subgroup of the enrolled subjects. We found enrichment of C16:0, C18:0, and C18:1 species and a depletion in C18:2 and C20:4 species in the plasma of carriers of two mutant LCAT alleles. No changes were observed in heterozygotes. Furthermore, plasma triglyceride-FA distribution was remarkably similar between carriers of LCAT deficiency and controls. CEFA distribution in VLDL essentially recapitulated that of plasma, being mainly enriched in C16:0 and C18:1, while depleted in C18:2 and C20:4. Finally, after fat loading, chylomicrons of carriers of two mutant LCAT alleles showed CEs containing mainly saturated FAs. This study of CEFA composition in a large cohort of carriers of LCAT deficiency shows that in the absence of LCAT-derived CEs, CEs present in apoB-containing lipoproteins are derived from hepatic and intestinal sterol O-acyltransferase 2.     

Respiratory enzymes in muscle: Interaction between environmental temperature, nutrition and growth

1. 1.In young pigs living at 35 or 10°C on a high or low energy intake, respiratory enzyme activities in longissimus dorsi muscle were greater both in the cold and on low intake. The elevated activities in the cold were unlikely to be related entirely to shivering since they were also found in muscle from the diaphragm.

2. 2.In a second study, pigs were kept close to thermal neutrality (26°C) on different levels of food intake and for different periods of time. For all animals, as body weight increased there was a decline in respiratory enzyme activity and the number of dark fibres in skeletal muscle. For those of the same weight, but different age and food intake, there was no difference in enzyme activity or number of dark fibres per unit area.

3. 3.At least part of the difference in respiratory enzyme activities related to energy intake must therefore be due to differences in body size. However, size is not the sole determinant of enzyme activity in skeletal muscle, since in animals of similar size those living at 10°C have greater enzyme activities than those at 35°C.

Dietary vitamin E and the response of rainbow trout, Oncorhynchus mykiss (Walbaum), to infection with Yersinia ruckeri

Rainbow trout fed diets containing 7, 86 or 806 mg vitamin E kg⁻¹ for 22 weeks were exposed to virulent Yersinia ruckeri by bath or injection. Mortalities were always least among those fed the highest concentration of vitamin E but serum antibody production was not affected by vitamin E levels.     

Investigations on the mechanism of hypercholesterolemia observed in copper deficiency in rats

The mechanism of hypercholesterolemia effect of Cu²⁺ deficiency was studied in rats. There was increased activity of hepatic hydroxymethylglutaryl-coenzyme A reductase and increased incorporation of labelled acetate into free cholesterol of liver in the Cu²⁺ deficient rats. Incorporation of label into ester cholesterol was however decreased in the liver. Concentration of bile acids in the liver was not significantly altered. Increase in the incorporation of labelled acetate into serum cholesterol and increase in the concentration of cholesterol and apo B in the low density lipoproteins + very low density lipoproteins fractions were observed. Activity of lipoprotein lipase of the extrahepatic tissues decreased in the Cu²⁺ deficient rats.     

Evidence for a branched respiratory system with two cytochrome oxidases in autotrophically grown Alcaligenes latus

The respiratory system of chemolithoautotrophically-grown Alcaligenes latus contains a, b, and c type cytochromes. Two cytochrome oxidases were identified by their carbon monoxide difference spectra and their differing sensitivities to cyanide and carbon monoxide. The oxidases were cytochrome o and an a-type cytochrome. Ubiquinone was present in A. latus membranes and could be reduced by H₂. The quinone analogue, 2-heptyl-4-hydroxy-quinoline-N-oxide (HQNO), was a strong inhibitor of the H₂ oxidase reaction, but did not prevent the reduction of either ubiquinone or the cytochromes.Abbreviations HQNO 2-heptyl-4-hydroxy-quinoline-N-oxide - TMPD N,N,N,N-tetramethyl-p-phenylenediamine     

Kinetic measurement of bacterial adherence to eukaryotic cells

We developed a kinetic assay using a monolayer of differentiated respiratory epithelium in culture to assess bacterial adherence. Mean residence time of bacteria in the tissue culture chamber was estimated from a model-independent (moment) analysis of the rate of bacterial washout from perfused Rose chambers. Results with this method compared favorably with visual assessment of adherence and double radiolabel method with H. influenzae. Adherence was assessed with low inoculae of H. influenzae, P. cepacia and P. aeruginosa avoiding cytotoxic effects seen when large inoculae are added to eukaryotic cells. This method will provide a means of assessing adherence of pathogenic respiratory bacteria to their cellular target at low inoculae.