Formation of a Tree having a Low Lignin Content

Received 30 September 2001/ Accepted in revised form 26 October 2001     

Hypophysiotropic neurons in the goldfish hypothalamus demonstrated by retrograde transport of horseradish peroxidase

Summary The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only — the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.     

Electrophoretic profiles of cyanobacterial membrane polypeptides showing heme-dependent peroxidase activity

The photosynthetic membranes of Anacystis nidulans R2 were examined electrophoretically following solubilization with lithium dodecyl sulfate. Electrophoresis yielded six prominent chlorophyll-containing bands. In addition, five polypeptides were observed which possessed heme-dependent peroxidase activity, monitored by incubating gels with 3,3′,5,5′-tetramethylbenzidine plus hydrogen peroxide. One such polypeptide, at 105 kdaltons, was removed by repeated washing of the membranes. Four remaining peroxidase-active polypeptides were observed at 7.2, 13.5, 18.5 and 33 kdaltons. Further examination of these four polypeptides yielded the following results. (1) The mobility of the 33 kdalton polypeptide was altered from 29 to 33 kdaltons upon heating (70°C) during membrane solubilization. (2) All four polypeptides showed stable heme-protein associations in the presence of 8 M urea; however, in the presence of urea, alterations in protein mobility were observed for each poly-peptide and only two (at 13.5 and 33 kdaltons) showed peroxidase activity following heating (70°C) during membrane solubilization. (3) The presence of thiols during membrane solubilization at 0°C was required to observe peroxidase activity at 7.2 kdaltons. These results, when compared to known properties of isolated cytochromes, suggest that the four polypeptides characterized here correspond to the subunits of photosynthetic cytochromes. Electrophoretic assessment of maize mutants lacking cytochrome f and b₆ activity supports this suggestion.     

Periplasmic superoxide dismutases in Aquaspirillum magnetotacticum

Aquaspirillum magnetotacticum MS-1 cells cultured microaerobically (dissolved O₂ tension 1% of saturation), expressed proteins with superoxide dismutase (SOD) activity. The majority (roughly 95%) of total cell superoxide dismutase activity was located in the cell periplasm with little or no activity in the cell cytoplasm. Irontype SOD (FeSOD) contributed 88% of the total activity activity detected, although a manganese-type SOD (MnSOD) was present in the periplasm as well. Cells cultured at a higher dissolved O₂ tension (10% of saturation) expressed increased activity of the MnSOD relative to that of the FeSOD.     

An analysis of substrate binding interactions in the heme peroxidase enzymes: A structural perspective

The interactions of heme peroxidase enzymes with their substrates have been studied for many years, but only in the last decade or so has structural information begun to appear. This review looks at crystal structures for a number of heme peroxidases in complex with a number of (mainly organic) substrates. It examines the nature and location of the binding interaction, and explores functional similarities and differences across the family.     

Enhancement of cytochrome c catalytic behaviour by affecting the heme environment using functionalized carbon-based nanomaterials

The effect of carbon-based nanomaterials (CBNs), such as multi-wall carbon nanotubes (CNTs) and graphene oxide (GO) nanomaterials functionalized with carboxyl, alkyl and amine groups, on the peroxidase-like activity and structure of cytochrome c (cyt c) was investigated. The catalytic efficiency of cyt c increases up to 78-fold in the presence of graphene oxide and up to 2.5-fold in the presence of other functionalized CBNs. Moreover, the use of functionalized CBNs enhances the thermal stability of the protein as well as its tolerance against hydrogen peroxide up to 2.5-fold. UV–vis and circular dichroism spectroscopy studies suggest that the increase in the peroxidase activity of cyt c in the presence of some functionalized GO nanomaterials, correlates to perturbations of the heme microenvironment, while the secondary structure of the enzyme remains intact. These results indicate that the beneficial effect the functionalized CBNs have on the activity and on the stability of cyt c depends on CBNs geometry and surface functionalization.     

Isolation of soil Streptomyces strains capable of degrading humic acids and analysis of their peroxidase activity

Abstract Fifteen Streptomyces strains capable of decolorizing humic acids in presence of glucose were isolated from soil samples using the dilute suspension technique and spread on agar plates. Six strains, displaying a significant and stable activity, were selected for further characterization. Some features of these isolates (carbon source utilization, enzyme production, antibiotic resistance) were compared with those of the reference strain Streptomyces viridosporus ATCC 39115. Degradation properties studied in batch cultures at pH 7.0 showed that the catabolic activity on humic acids was generally stimulated by incubation with 100% oxygen and was cell surface-associated. Peroxidase activity from cell-free extracts was analysed by using the oxidation of N,N,N′,N′-tetramethyl-phenylene-diamine. PAGE analysis revealed the existence of two major types of peroxidases (molecular mass: about 39.2 and 61.6 kDa), dividing the strains into two groups. The role of cell surface-associated peroxidase activity in the breakdown of humic acids is discussed.     

A biophysical characterization of the iron coordination environment in wheat germ peroxidase

 The heme protein wheat germ peroxidase (isoenzyme C₂) and its cyanide-inhibited form have been investigated by means of electronic, CD and paramagnetic NMR spectroscopy. The data indicate a protein environment of the active site distinct from that of horseradish peroxidase (HRP), with a larger solvent accessibility. The iron is pentacoordinated at neutral and low pH, whereas a hydroxyl anion may be bound at alkaline pH. The fifth axial ligand is a His residue with a partial anionic character, as found in other peroxidases. A spin equilibrium is observed at high enzyme concentrations. Received: 17 September 1996 / Accepted: 10 January 1997     

The Chlorite Dismutase (HemQ) from Staphylococcus aureus Has a Redox-sensitive Heme and Is Associated with the Small Colony Variant Phenotype

The chlorite dismutases (C-family proteins) are a widespread family of heme-binding proteins for which chemical and biological roles remain unclear. An association of the gene with heme biosynthesis in Gram-positive bacteria was previously demonstrated by experiments involving introduction of genes from two Gram-positive species into heme biosynthesis mutant strains of Escherichia coli, leading to the gene being renamed hemQ. To assess the gene product''s biological role more directly, a Staphylococcus aureus strain with an inactivated hemQ gene was generated and shown to be a slow growing small colony variant under aerobic but not anaerobic conditions. The small colony variant phenotype is rescued by the addition of exogenous heme despite an otherwise wild type heme biosynthetic pathway. The ΔhemQ mutant accumulates coproporphyrin specifically under aerobic conditions. Although its sequence is highly similar to functional chlorite dismutases, the HemQ protein has no steady state reactivity with chlorite, very modest reactivity with H₂O₂ or peracetic acid, and no observable transient intermediates. HemQ''s equilibrium affinity for heme is in the low micromolar range. Holo-HemQ reconstituted with heme exhibits heme lysis after <50 turnovers with peroxide and <10 turnovers with chlorite. The heme-free apoprotein aggregates or unfolds over time. IsdG-like proteins and antibiotic biosynthesis monooxygenases are close sequence and structural relatives of HemQ that use heme or porphyrin-like organic molecules as substrates. The genetic and biochemical data suggest a similar substrate role for heme or porphyrin, with possible sensor-regulator functions for the protein. HemQ heme could serve as the means by which S. aureus reversibly adopts an SCV phenotype in response to redox stress.