Investigation of the S3 electron paramagnetic resonance signal from the oxygen-evolving complex of photosystem 2: effect of inhibition of oxygen evolution by acetate.

An S3 electron paramagnetic resonance (EPR) signal is observed in a variety of photosystem 2 (PS2) samples in which the oxygen-evolving complex (OEC) has been inhibited. These signals have been proposed to be due to an interaction, S2X+, between the manganese cluster in an oxidation state equivalent to S2 and an organic radical, either oxidized histidine [Boussac et al. (1990) Nature 347, 303-306] or the tyrosine radical Yz+ [Hallahan et al.

Characterization of the Brassica campestris mitochondrial gene for subunit six of NADH dehydrogenase: nad6 is present in the mitochondrion of a wide range of flowering plants.

We have isolated the Brassica campestris mitochondrial gene nad6, coding for subunit six of NADH dehydrogenase. The deduced amino-acid sequence of this gene shows considerable similarity to mitochondrially encoded NAD6 proteins of other organisms as well as to NAD6 proteins coded for by plant chloroplast DNAs. The B.

Spectroscopic studies of the manganese complex of Photosystem II.

Our recent EPR and EXAFS experiments investigating the structure of the oxygen-evolving complex of PS II are discussed. PS II treatments which affect the cofactors calcium and chloride have been used to poise samples in modified forms of the S-states, S1, S2 and S3. X-ray absorption studies indicate a similar overall structure for the manganese complex between treated and native samples although the influence of the treatments and cofactors is observed.

Modeling alpha-helical transmembrane domains: the calculation and use of substitution tables for lipid-facing residues.

Amino acid substitution tables are calculated for residues in membrane proteins where the side chain is accessible to the lipid. The analysis is based upon the knowledge of the three-dimensional structures of two homologous bacterial photosynthetic reaction centers and alignments of their sequences with the sequences of related proteins. The patterns of residue substitutions show that the lipid-accessible residues are less conserved and have distinctly different substitution patterns from the inaccessible residues in water-soluble proteins.

Photoinhibition affects the non-heme iron center in photosystem II.

Effects on the PS II acceptor side caused by exposure to strong white light (180 W/m2) of PS II membrane fragments (spinach) at pH 6.5 and 0 degrees C were analyzed by measuring low temperature EPR signals and flash-induced transient changes of the fluorescence quantum yield. The following results were obtained: (a) the extent of the light induced g = 1.

A three-dimensional model of the Photosystem II reaction centre of Pisum sativum.

A three-dimensional model of the core proteins D1 and D2, including the cofactors, that form the Photosystem II reaction centre of pea (Pisum sativum), has been generated. This model was built with a rule-based computer modelling system using the information from the crystal structures of the photosynthetic reaction centres of Rhodopseudomonas viridis and Rhodobacter sphaeroides. An alignment of the primary sequences of twenty three D1, nine D2, eight bacterial L and eight bacterial M subunits predicts strong similarity between bacterial and higher plant reaction centres, especially in the transmembrane region where the cofactors responsible for electron transport are located.

An e.x.a.f.s. study of the manganese O2-evolving complex in purified Photosystem II membrane fractions. The S1 and S2 states.

Manganese K-edge X-ray spectra have been obtained for Photosystem II samples isolated using Triton X-100 detergent and samples further purified by n-heptyl beta-D-thioglucoside detergent treatment to remove light-harvesting polypeptides and low-affinity calcium. The structure of the manganese complex is very similar for the two detergent preparations used. Analysis of the e.

Cytochrome b-245 is a flavocytochrome containing FAD and the NADPH-binding site of the microbicidal oxidase of phagocytes.

The NADPH oxidase of phagocytic cells is important for the efficient killing and digestion of ingested microbes. A very unusual low-potential cytochrome b (b-245) is the only redox molecule to have been identified in this system. The FAD-containing flavoprotein that binds NADPH and transfers electrons to the cytochrome has eluded identification for three decades.

Investigation of the origin of the "S3" EPR signal from the oxygen-evolving complex of photosystem 2: the role of tyrosine Z.

The origin of the "S3" EPR signal from calcium-depleted photosystem 2 samples has been investigated. This signal is observed after freezing samples under illumination and has been assigned to an interaction between the manganese cluster and an oxidized histidine radical [Boussac et al. (1990) Nature 347; 303-306].

Interactions of Avocado (Persea americana) Cytochrome P-450 with Monoterpenoids.

The microsomal fraction of avocado (Persea americana) mesocarp is a rich source of cytochrome P-450 active in the demethylation of xenobiotics. Cytochrome P-450 from this tissue has been purified and well characterized at the molecular level (DP O'Keefe, KJ Leto [1989] Plant Physiol 89: 1141-1149; KR Bozak, H Yu, R Sirevag, RE Christoffersen [1990] Proc Natl Acad Sci USA 87: 3904-3908). Despite this extensive characterization, the role of the enzyme in vivo was not established.

Characterization of the multiple EPR line shapes of iron-semiquinones in photosystem 2.

We have compared the temperature-dependence characteristics of the EPR signals of Qa and Qb iron-semiquinones from both purple bacterial and plant photosystems. The data obtained were analyzed and estimates of the splitting parameters of the non-heme Fe2+ spin sublevels obtained. The study confirms the similarities of the g = 1.

RNA-mediated transfer of the gene coxII from the mitochondrion to the nucleus during flowering plant evolution.

The gene coxII, normally present in the mitochondrion, was functionally transferred to the nucleus during flowering plant evolution. coxII transfer is estimated to have occurred between 60 and 200 million years ago, whereas loss of coxII from the mitochondrion occurred much more recently, being restricted to a single genus of legumes. Most legumes have coxII in both the nucleus and the mitochondrion; however, no evidence is found for simultaneous coxII expression in both compartments.

Conserved structural motifs in cyclins identified by sequence analysis.

Cyclins, as regulatory subunits of the ubiquitous p34cdc2 protein kinase, act as key controlling elements of the eukaryotic cell cycle. We have examined published sequences of A- and B-type cyclins for both amino acid and secondary structure homologies. In particular, we sought regions of homology outside the recognised area of sequence conservation known as the "cyclin box', as well as conserved features predicted to lie at the protein surface.

Functional size measurements of the ubiquinol oxidase activity of the cytochrome o terminal oxidase complex of Escherichia coli.

The functional molecular mass for ubiquinol-1 oxidation by the Escherichia coli terminal oxidase, cytochrome o, was determined by radiation-inactivation analysis of membranes from a cytochrome d-deficient mutant. The functional molecular mass for ubiquinol-l oxidase activity was found to be 38.3 +/- 2.

Old age security and the defense of social norms.

This paper identifies various kinds of risk and uncertainty observable in rural areas of developing countries and explains the relative importance of those pertaining to disability and old age. It compares the modern system (based on old age pensions and social security) for mitigating or coping with these risks with the traditional intrafamilial support mechanisms. The paper concludes that, when the traditional system is functioning smoothly, it can address these needs at far lower cost than the modern system.

Significance of capillary basement membrane changes in diabetes mellitus.

Diabetes mellitus is a disease in which the capillary basement membranes are substantially altered. This diabetic microangiopathy is characterized by a thickening of the basement membrane and changes in its permeability characteristic due to a disturbance in the production and distribution of its functional components. Glucose metabolism and insulin imbalance have been implicated in these basement membrane modifications.

Isolated posterior malleolar ankle fractures.

The isolated posterior malleolar fracture is a genuine clinicopathologic entity, albeit a relatively rare one. Frequency of occurrence is approximately 1% of all reported ankle fractures. It can be mechanistically explained within the parameters of the Lauge-Hansen classification.

Identification of the haem-binding subunit of cytochrome b-245.

Cytochrome b-245 from neutrophil plasma membranes contains two types of subunit with apparent molecular masses from gel electrophoresis in the presence of SDS of 23 kDa and 76-92 kDa. Radiation-inactivation analysis revealed a single-exponential decay process for the visible absorption of the haem chromophore in the membrane, corresponding to a molecular mass of 21 +/- 5 kDa for the haem-containing polypeptide chain. Sedimentation equilibrium of the cytochrome solubilized by the detergent Triton N101 showed that the protein was polydisperse, with a molecular mass of approx.

Contraceptive practice of Irish married and single first-time mothers.

This study surveys 100 married and 100 unmarried primiparous mothers, attending the National Maternity Hospital, Dublin, with regard to their contraceptive practice, their planning of their pregnancy and the timing of their first antenatal visit. Nineteen per cent of the married women, but 64% of the unmarried women, had never used any contraceptive method. The contraceptive pill was the most popular method for both groups, but while three in five of the married women had at some time used the pill, only a little more than one in five of the unmarried women had ever used it.

Medial displacement osteotomy for unstable intertrochanteric fractures. Twenty years later.

Fifty-five unstable intertrochanteric fractures were treated with a sliding compression screw apparatus. Thirty-seven cases were treated by anatomic nailing and 18 cases were treated by primary medial displacement osteotomy (MDO) by the method of Dimon and Hughston. The mean age of these patients was 82.

Location, identity, amount and serial entry of chloroplast DNA sequences in crucifer mitochondrial DNAs.

Southern blot hybridization techniques were used to examine the chloroplast DNA (cpDNA) sequences present in the mitochondrial DNAs (mtDNAs) of two Brassica species (B. campestris and B. hirta), two closely related species belonging to the same tribe as Brassica (Raphanus sativa, Crambe abyssinica), and two more distantly related species of crucifers (Arabidopsis thaliana, Capsella bursa-pastoris).