Phospholipid dependence of the anion transport system of the human erythrocyte membrane. Studies on reconstituted band 3/lipid vesicles

Band 3 protein extracted from human erythrocyte membranes by Triton X-100 was recombined with the major classes of phospholipid occurring in the erythrocyte membrane. The resulting vesicle systems were characterized with respect to recoveries, phospholipid composition, protein content and vesicle size as well as capacity and activation energy of sulfate transport. Transport was classified into band-3-specific fluxes and unspecific permeability by inhibitors. Transport numbers (sulfate ions per band 3 per minute) served as a measure of functional recovery after reconstitution. The transport properties of band 3 proved to be insensitive to replacement of phosphatidylcholine by phosphatidylethanolamine, while sphingomyelin and phosphatidylserine gradually inactivated band-3-specific anion transport when present at mole fractions exceeding 30 mol%. The activation energy of transport remained unaltered in spite of the decrease in transport numbers. The results, which are discussed in terms of requirements of band 3 protein function with respect to the fluidity and surface charge of its lipid environment, provide a new piece of evidence that the transport function of band 3 protein depends on the properties of its lipid environment just as the catalytic properties of some other membrane enzymes. The well-established species differences in anion transport (Gruber, W. and Deuticke, B. (1973) J. Membrane Biol. 13, 19–36) may to some extent reflect this lipid dependence.     

Hyperprolactinaemia and testosterone production. Observations in 2 men on long-term dialysis

2 men had received maintenance dialysis for more than 5 years because of uraemia. Gradual impairment of libido had led to total impotence of more than 6 months duration. Concurrently hyperprolactinaemia occurred. Bromocriptine was given for 2 and 4 months, respectively. Potency was not restored, but in 1 patient the blood transfusion requirements were halved and general well-being and strength increased. In both men, the serum prolactin levels normalized. Inversely, the low plasma testosterone levels increased during the treatment period.     

The effect of light on the growth rate of intertidal Acropora pulchra (Brook) from Phuket,Thailand, lat. 8°N

Series of apices of Acropora pulchra from an intertidal reef at Phuket, Thailand, were grown at different depths in the sea, and the length growth was monitored at 12–24 h intervals with laser diffraction. The growth rates of actively growing apices were normally distributed and showed a high variability, with an average coefficient of variation of 58%. There was a highly significant difference in average growth rate between adjacent colonies. A significant linear relationship was found between irradiance and length growth, with a saturating level at 300–400 Wm^-2. At 1000 Wm^-2 length growth was significantly reduced. Under normal daylight conditions, day and night growth rates were equal.     

Dose-response function for Painter's SCE-model

Summary The replication model for sister chromatid exchange (SCE), when introduced in 1980 by Painter, was claimed to be consistent with the one hit property of SCE. However, the argument offered in favour of the one hit property was based on a defective dose-response function, as shown in this paper, since dose as the independent parameter of any dose-response function was not included in the considerations. This missing part of the model's dose-response function is added and, by using Bessel functions, a formula for the complete dose-response function is presented. A re-examination of the newly derived function shows that, in the model, linearity holds only under certain restricted circumstances.     

Regulation of thyroid hormone metabolism in rat liver fractions

The nature of the conversion of thyroxine (T₄) to triiodothyronine (T₃) and reverse triiodothyronine (rT₃) was investigated in rat liver homogenate and microsomes. A 6-fold rise of T₃ and 2.5-fold rise of rT₃ levels determined by specific radioimmunoassays was observed over 6 h after the addition of T₄. An enzymic process is suggested that converts T₄ to T₃ and rT₃. For T₃ the optimal pH is 6 and for rT₃, 9.5. The converting activity for both T₃ and rT₃ is temperature dependent and can be suppressed by heat, H₂O₂, merthiolate and by 5-propyl-2-thiouracil. rT₃ and to a lesser degree iodide, were able to inhibit the production of T₃ in a dose related fashion. Therefore the pH dependendy, rT₃ and iodide may regulate the availability of T₃ or rT₃ depending on the metabolic requirements of thyroid hormones.     

Inhibitory effect of cortisone acetate on the stimulation of rat liver cytosol l-serine Pyruvate aminotransferase by dibutyryl adenosine 3′,5′-monophosphate

An injection of cortisone acetate at a dose of 5 mg/100 g body weight concomitant with dibutryl cyclic AMP prevents the increase in the activity of rat liver cytosol serine aminotransferase (L-serine: pyruvate aminotransferase, EC 2.6.1.51) elicited by the nucleotide with a lag of about 2 h. If the glucocorticoid is given 2 h prior to the nucleotide inducer, the lag disappears. The inhibitory effect of cortisone acetate gradually decays and is no longer detectable 12 h following its administration. Theophylline, insulin and glucose at doses which affect significantly the level of tyrosine aminotransferase, have no effect on the level of serine aminotransferase and on the cortisone inhibition. The inhibitory effect of the glucocorticoid on the dibutyryl cyclic AMP-mediated increase in serine aminotransferase diminishes with the age of animals. Increase in the enzyme activity by a single dose of glucagon can also be inhibited by cortisone acetate and actinomycin D as in the case with dibutyrl cyclic AMP as an inducer. The possibility of the existence of a specific inhibitory factor which is formed in response to cortisone acetate is discussed.     

Pollen–plant–climate relationships in sub-Saharan Africa

Aim  To demonstrate that incorporating the bioclimatic range of possible contributor plants leads to improved accuracy in interpreting the palaeoclimatic record of taxonomically complex pollen types.
Location  North Tropical Africa.
Methods  The geographical ranges of selected African plants were extracted from the literature and geo-referenced. These plant ranges were compared with the pollen percentages obtained from a network of surface sediments. Climate-response surfaces were graphed for each pollen taxon and each corresponding plant species.
Results  Several patterns can be identified, including taxa for which the pollen and plant distributions coincide, and others where the range limits diverge. Some pollen types display a reduced climate range compared with that of the corresponding plant species, due to low pollen production and/or dispersal. For other taxa, corresponding to high pollen producers such as pioneer taxa, pollen types display a larger climatic envelope than that of the corresponding plants. The number of species contained in a pollen taxon is an important factor, as the botanical species included in a taxon may have different geographical and climate distributions.
Main conclusions  The comparison between pollen and plant distributions is an essential step towards more precise vegetation and climate reconstructions in Africa, as it identifies taxa that have a high correspondence between pollen and plant distribution patterns. Our method is a useful tool to reassess biome reconstructions in Africa and to characterize accurately the vegetation and climate conditions at a regional scale, from pollen data.     

Phase memory relaxation times of spin labels in human carbonic anhydrase II: pulsed EPR to determine spin label location.

Phase memory relaxation times (T(M) or T(2)) of spin labels in human carbonic anhydrase II (HCA II) are reported. Spin labels (N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrrolidinyl)iodoacetamide, IPSL) were introduced at cysteines, by site-directed mutagenesis at seven different positions in the protein. By two pulse electron paramagnetic resonance (EPR), electron spin echo decays at 45 K are measured and fitted by stretched exponentials, resulting in relaxation parameters T(M) and x. T(M) values of seven positions are between 1.6 micros for the most buried residue (L79C) and 4.7 micros for a residue at the protein surface (W245C). In deuteriated buffer, longer T(M) are found for all but the most buried residues (L79C and W97C), and electron spin echo envelop modulation (ESEEM) of deuterium nuclei is observed. Different deuterium ESEEM patterns for W95C and W16C (surface residue) indicate differences in the local water concentration, or accessibility, of the spin label by deuterium. We propose T(M) as a parameter to determine the spin label location in proteins. Furthermore, these systems are interesting for studying the pertaining relaxation mechanism.     

Exopolysaccharide-producing strains of thermophilic lactic acid bacteria cluster into groups according to their EPS structure

AIMS: To compare galactose-negative strains of Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs). METHODS AND RESULTS: The structures of the EPSs were determined using nuclear magnetic resonance (NMR) and their genetic relationships determined using restriction endonuclease analysis (REA) and random amplification of polymorphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and each group produced an EPS with a particular subunit structure. CONCLUSION: Although none of the strains assimilated galactose, all inserted a high proportion of galactose into their EPS when grown in skimmed milk, and fell into three distinct groups. Significance and Impact of the Study: This information should help in an understanding of genetic exchanges in lactic acid bacteria.     

Activation of mercuric reductase by the substrate NADPH

Preincubation of the oxidized form of the flavoenzyme mercuric reductase with the reducing substrate, NADPH, or with a high concentration of cysteine (30 mM) results in a substantial increase of the catalytic activity as measured in a standard spectrophotometric assay. Also NADH has some activating effect but NADP+ or EDTA have no effect. In the presence of 1 mM cysteine only one equivalent of NADPH per FAD seems to be required for full activation which occurs after an incubation time of about 10 min. Activated mercuric reductase appears to be stable under anaerobic conditions but eventually returns to the original level of activity in the presence of oxygen. The activated state seems to be stabilized by 1 mM cysteine. Activation of mercuric reductase does not seem to be correlated with a change in the number of reactive thiol groups. The chemical nature of the activation process is not yet understood. Stopped-flow studies have shown that the nonactivated enzyme is practically inactive prior to contact with the substrates. The enzyme is gradually activated during the assay. The kinetics of activation of the 'native' enzyme is biphasic but 'clipped' enzyme, lacking an 85-residue N-terminal domain, is activated in a single first-order process. The progress curves obtained with preactivated enzyme are approximately exponential even at saturating concentrations of NADPH (Km = 0.4 microM at 25 degrees C, pH 7.3) and Hg2+ (Km = 3.2 microM in the presence of 1 mM cysteine). The initial rates yield kcat values of about 13 s-1 per FAD molecule (25 degrees C, pH 7.3). We find no evidence for a thiol-dependent change from a rapid to a slow kinetic phase. The shape of the progress curves presumably depends on product inhibition, but NADP+ is not a sufficiently effective inhibitor to explain the effect fully.