Iron and the liver. Acute and long-term effects of iron-loading on hepatic haem metabolism.

We have determined the dose-response curves (100-900 mg of Fe/kg body wt.) and the time course over 84 days for the effects of a single injection of iron-dextran on rat hepatic 5-aminolaevulinate synthetase, cytochrome P-450, iron content, and GSH (reduced glutathione). Porphyrins in liver and urine have also been measured. (1) At 2 days after treatment, a dose of 500 mg of Fe/kg produced a 20-fold increase in iron concentration, which was maintained for 14 days. Total hepatic iron remained constant over 63 days, falling slightly by 84 days. (2) The activity of 5-aminolaevulinate synthetase was maximally increased (6-fold) 12-24 h after iron treatment. By 48 h the activity fell to less than twice the control value and thereafter remained slightly above the control value (1.1-1.5-fold) until 84 days after iron treatment. Liver GSH concentrations were unaffected by iron. Porphyrins in liver and urine were either unchanged or decreased. (3) Hepatic cytochrome P-450 decreased after iron treatment to a minimum (63% of control) at 48 h after iron administration and gradually returned to the control value by 28 days. (4) Iron-dextran potentiated 2 allyl-2-isopropyl-acetamide-induced synthesis of hepatic 5-aminolaevulinate. Potentiation occurred if the drug was given at the same time or 36 h after iron administration, but did not occur if the drug was given 14 or 64 days after iron administration. (5) The results are discussed in relation to proposed mechanisms for the effects of iron on hepatic haem metabolism.     

Characterisation of a short,highly repeated and centromerically localised DNA sequence in crested and marbled newts of the genus Triturus

A 32–33 bp highly repeated DNA sequence, TkS1, has been isolated from genomic DNA of the newt Triturus karelini digested with the restriction endonucleases HaeIII or AluI. TkS1 is known to be localised in the centromeric heterochromatin of all the chromosomes in T. karelini and the related species T. cristatus TkS1 has been shown to be present in varying amounts in the genomic DNA of a range of species of Triturus, including representatives of the two main subgenera Triturus and Palaeotriton. A programme of sequencing of monomers, dimers and trimers of TkS1 was carried out in order to determine the level of conservation of the sequence within and between species of Triturus. Altogether 204 monomer (32/33 bp) clones were made of TkS1 from three individuals of T. karelini, and one individual each of T. cristatus, T. carnifex, T. dobrogicus and T. marmoratus, all members of the subgenus Triturus and the cristatus species group. A number of dimer (64 bp) and trimer (96 bp) clones were also made from DNA of a single specimen of T. karelini digested with HaeIII or AluI. Three distinct types of TkS1 were identified in all species examined, except for T. marmoratus where only two of the types were found. The types were distinguished on the basis of certain recurring divergent patterns in monomers sequenced from T. karelini. Type 1 is mainly characterised by the presence of an AluI site at positions 24–27 and type 3 mainly by the presence of an additional base (C) at position 14. Type 2 normally lacks the AluI site and the C at position 14, as well as having a number of other distinguishing features. TkS1 and its three types have remained remarkably constant in sequence since before the divergence of T. marmoratus from other species in the cristatus species group, about 10 million years ago. Examination of all 204 monomer clones and comparison with consensus sequences for the three types shows less than 5% divergence at any one position in the sequence. There is good evidence from examination of dimer and trimer clones of TkS1 that the different types are intermingled with each other, and all three types are likely to be present on all chromosomes. Dimeric (64 bp) TkS1 clones constructed from AluI fragments of T. karelini DNA show evidence of a trimeric (96 bp) supertype with the pattern type 1-type 3-type 1 that is much more common than would be expected on a random basis. The properties of TkS1 are discussed in relation to models for the involvement of highly repeated satellite DNA in chromosomal growth and evolution.W. Hennig     

The human cytomegalovirus 80-kilodalton but not the 72-kilodalton immediate-early protein transactivates heterologous promoters in a TATA box-dependent mechanism and interacts directly with TFIID.

We have asked how the human cytomegalovirus major immediate-early 1 (IE1) and 2 (IE2) proteins act to transactivate heterologous cellular and viral promoters. Here we show that transactivation of the human immunodeficiency virus long terminal repeat and the 70,000-molecular-weight heat shock protein (hsp70) promoter by IE1 is TATA box independent and that the IE1 protein does not interact directly with the TATA box-binding factor TFIID. Conversely, transactivation of these promoters by IE2 is TATA box dependent and a direct interaction between IE2 and TFIID occurs, suggesting that IE2 transactivation is mediated through interaction with TFIID.     

Haloperoxidase activity of Phanerochaete chrysosporium lignin peroxidases H2 and H8.

Monochlorodimedone (MCD), commonly used as a halogen acceptor for haloperoxidase assays, was oxidized by hydrogen peroxide in the presence of lignin peroxidase isoenzymes H2 and H8. When oxidized, it produced a weak absorption band with an intensity that varied with pH. This absorbance was used as a simple method for the product analysis because it disappeared when MCD was brominated or chlorinated. We assessed the activity of the lignin peroxidases for oxidation of bromide by measuring the bromination of MCD, the formation of tribromide, the bromide-mediated oxidation of glutathione, and the bromide-mediated catalase-like activity. We analyzed the reaction products of MCD and the halide-mediated oxidation of glutathione when bromide was replaced by chloride. These enzymes demonstrated no significant activity for oxidation of chloride. Unlike other peroxidases, the lignin peroxidases exhibited similar pH-activity curves for the iodide and bromide oxidations. The optimum pH for activity was about 2.5. Surprisingly, this pH dependence of lignin peroxidase activity for the halides was nearly the same in the reactions with hydrogen donors, such as hydroquinone and guaiacol. The results suggested that protonation of the enzymes with pKa approximately 3.2 is necessary for the catalytic function of lignin peroxidases, irrespective of whether the substrates are electron or hydrogen donors. These unique reaction profiles of lignin peroxidases are compared to those of other peroxidases, such as lactoperoxidase, bromoperoxidase, chloroperoxidase, and horseradish peroxidase. Isozyme H2 was more active than isozyme H8, but isozyme H8 was more stable at very acidic pH.     

Relation between diameter and flow in major branches of the arch of the aorta.

In the analysis of arterial branching the classical "cube law' has provided a working model for the relation between the diameter of a blood vessel and the flow which the vessel carries on a long-term basis. The law has shown good agreement with biological data, but questions remain regarding its applicability to all levels of the arterial tree. The present study tests the hypothesis that the cube law may not be valid in the first few generations of the arterial tree, where vessel capacitance and gross anatomy may play important roles. Biological data have shown some support for this hypothesis in the past but the heterogeneity characteristic of past data has not allowed a conclusive test so far. We present new data which have been obtained from the same location on the arterial tree and in sufficient number to make this test possible for the first time. Also, while past tests have been based primarily on correlation of the measured data with an assumed power law, we show here that this can be misleading. The present data allow a simpler test which does not involve correlation and which leads to more direct conclusions. For the vessels surveyed, the results show unequivocally that the relation between diameter and flow is governed by a 'square law' rather than the classical cube law. Coupled with past findings this suggests that the square law may apply at the first few levels of the arterial tree, while the cube law continues from there to perhaps the precapillary levels.     

Production of Eicosapentaenoic Acid (20:5 n-3) by Vibrio pelagius Isolated from Turbot (Scophthalmus maximus (L.)) Larvae

Fourteen bacterial strains isolated from turbot, Scophthalmus maximus (L.), larvae were screened for eicosapentaenoic acid (20:5 n-3) (EPA) production. Gas chromatography analysis revealed that one bacterial species, Vibrio pelagius, contained a high proportion of EPA in cellular lipid. This finding was confirmed by gas chromatography-mass spectrometry analysis. A higher concentration of EPA was detected when the bacterium was cultured at 4°C.     

Water Use Efficiency of Field-grown Maize during Moisture Stress

Theoretical analysis of the CO₂ assimilation and water loss by single leaves suggests that the water use efficiency of C₄ species decreases as stomatal resistance increases. To confirm this hypothesis for a complete maize crop, results from computer simulations and a field experiment were compiled for varying stomatal resistances. A soil-plant-atmosphere model allowed simulations of the many simultaneous interactions between a crop canopy and its environment. The simulations for varying stomatal resistances clearly indicated that as stomatal resistance increased, water use efficiency of the maize crop decreased. The field experiment data also confirmed that water use efficiency was significantly decreased under water stress conditions when stomatal resistance increased. We concluded that management practices for maize, which induce moisture stress conditions resulting in increased stomatal resistance, reduce both crop photosynthetic productivity and water use efficiency.     

Fluctuations in leaf water balance,with a period of 1 to 10 minutes

Summary Water uptake into leaves, and water vapour efflux from leaves, were found to show short-term fluctuations. The fluctuations were observed in a number of parameters of leaf water metabolism. It is suggested that this behaviour is a result of time lags in the transmission of changes in water potential through the leaf.