Neutron beam effects on spin-exchange-polarized 3He.

We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal spin-exchange-polarized 3He cells used as neutron spin filters. This was first observed as a reduction of the maximum attainable 3He polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at Los Alamos Neutron Science Center and Institute Laue-Langevin. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as sqrt[phi_{n}], where phi_{n} is the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the concentration of electron-ion pairs but is much larger than expected from earlier work.

The Involvement of Aspartate and Glutamate in the Decarboxylation of Malate by Isolated Bundle Sheath Chloroplasts from Zea mays.

Aspartate or glutamate stimulated the rate of light-dependent malate decarboxylation by isolated Zea mays bundle sheath chloroplasts. Stimulation involved a decrease in the apparent K(m) (malate) and an increased maximum velocity of decarboxylation. In the presence of glutamate other dicarboxylates (succinate, fumarate) competitively inhibited malate decarboxylation by intact chloroplasts with respect to malate with an apparent K(i) of about 6 millimolar. For comparison the K(i) for inhibition of nicotinamide adenine dinucleotide phosphate-malic enzyme from freshly lysed chloroplasts by these dicarboxylates was 15 millimolar. A range of compounds structurally related to aspartate stimulated malate decarboxylation by intact chloroplasts. K(a) values for stimulation at 5 millimolar malate were 1.7, 5, and 10 millimolar for l-glutamate, l-aspartate, and beta-methyl-dl-aspartate, respectively. Certain compounds, notably cysteic acid, which stimulated malate decarboxylation by intact chloroplasts inhibited malate decarboxylation by nicotinamide adenine dinucleotide phosphate-malic enzyme obtained from lysed chloroplasts and assayed under comparable conditions. It was concluded that aspartate, glutamate, and related compounds affect the transport of malate into the intact chloroplasts and that malate translocation does not take place on the general dicarboxylate translocator previously reported for higher plant chloroplasts.

Inhibited light activation of fructose and sedoheptulose bisphosphatase in spinach chloroplasts exposed to osmotic stress.

The light activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) and sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) was inhibited in isolated intact spinach (Spinacia oleracea L.) chloroplasts exposed to reduced osmotic potentials. Decreases in the velocity and magnitude of light activation correlated with the overall reduction in CO2 fixation rates. Responses of osmotically stressed chloroplasts to both varying pH and exogeous dihydroxyacetone phosphate (DHAP) or 3-phosphoglycerete (PGA) were examined. In the presence of DHAP, the absolute rate of CO2 fixation was increased and this increase was most pronounced at alkaline pH. Enhanced light activation of these enzymes was also observed under these conditions. However, in the presence of PGA, similar increases in photosynthetic rate and enzyme activation were not evident. Light-dependent stromal alkalization was unaffected by the stress treatments. Inhibition of light activation under hypertonic conditions is discussed in terms of substrate availability, possible alterations of the redox state of ferredoxin and associated electron carriers, and inhibited enzyme-enzyme or enzyme-substrate interactions involved in the light activation process.

CO(2) Assimilation and Malate Decarboxylation by Isolated Bundle Sheath Chloroplasts from Zea mays.

Conditions for optimal CO(2) fixation and malate decarboxylation by isolated bundle sheath chloroplasts from Zea mays were examined. The relative rates of these processes varied according to the photosynthetic carbon reduction cycle intermediate provided. Highest rates of malate decarboxylation, measured as pyruvate formation, were seen in the presence of 3-phosphoglycerate, while carbon fixation was highest in the presence of dihydroxyacetone phosphate; only low rates were measured with added ribose-5-phosphate. Chloroplasts exhibited a distinct phosphate requirement and this was optimal at a level of 2 millimolar inorganic phosphate in the presence of 2.5 millimolar 3-phosphoglycerate, dihydroxyacetone phosphate, or ribose-5-phosphate. Malate decarboxylation and CO(2) fixation were stimulated by additions of AMP, ADP, or ATP with half-maximal stimulation occurring at external adenylate concentrations of about 0.15 millimolar. High concentrations (>1 millimolar) of AMP were inhibitory. Aspartate included in the incubation medium stimulated malate decarboxylation and CO(2) assimilation. In the presence of aspartate, the apparent Michaelis constant (malate) for malate decarboxylation to pyruvate by chloroplasts decreased from 6 to 0.67 millimolar while the calculated V(max) for this process increased from 1.3 to 3.3 micromoles per milligram chlorophyll. Aspartate itself was not metabolized. It was concluded that the processes mediating the transport of phosphate, 3-phosphoglycerate, and dihydroxyacetone phosphate transport on the one hand, and also of malate might differ from those previously described for chloroplasts from C(3) plants.

Isolation of Bundle Sheath Cell Chloroplasts from the NADP-ME Type C(4) Plant Zea mays: Capacities for CO(2) Assimilation and Malate Decarboxylation.

Bundle sheath chloroplasts have been isolated from Zea mays leaves by a procedure involving enzymic digestion of mechanically prepared strands of bundle sheath cells followed by gentle breakage and filtration. The resulting crude chloroplast preparation was enriched by Percoll density layer centrifugation to yield intact chloroplasts (about 20 micrograms chlorophyll per 10-gram leaf tissue) with high metabolic activities. Based on activities of marker enzymes in the chloroplast and bundle sheath cell extracts, the chloroplasts were essentially free of contamination by other organelles and cytoplasmic material, and were generally about 70% intact. Chlorophyll a/b ratios were high (about 10). With appropriate substrates these chloroplasts displayed high rates of malate decarboxylation, measured as pyruvate formation, and CO(2) assimilation (maximum rates approximately 5 and 3 micromoles per minute per milligram chlorophyll, respectively). These activities were light dependent, linear for at least 20 minutes at 30 degrees C, and displayed highest rates at pH 8.0. High metabolic rates were dependent on addition of an exogenous source of carbon to the photosynthetic carbon reduction cycle (3-phosphoglycerate or dihydroxyacetone phosphate) and a nucleotide (ATP, ADP, or AMP), as well as aspartate. Generally, neither malate decarboxylation nor CO(2) assimilation occurred substantially in the absence of the other activity indicating a close relationship between these processes. Presumably, NADPH required for the photosynthetic carbon reduction cycle is largely supplied during the decarboxylation of malate by NADP-malic enzyme. The results are discussed in relation to the role of bundle sheath chloroplasts in C(4) photosynthesis by species of the NADP-malic enzyme type.

Metabolite levels in the stroma of spinach chloroplasts exposed to osmotic stress: Effects of the pH of the medium and exogenous dihydroxyacetone phosphate.

The levels of stromal photosynthetic intermediates were measured in isolated intact spinach (Spinacia oleracea L.) chloroplasts exposed to reduced osmotic potentials. Stressed chloroplasts showed slower rates of metabolite accumulation upon illumination than controls. Relative to other metabolites sedoheptulose-1,7-bisphosphate (SBP) and fructose-1,6-bisphosphate (FBP) accumulated in the stroma in the stressed treatments. Under these conditions 3-phosphoglycerate (3-PGA) efflux to the medium was restricted. Chloroplasts previously incubated with [(32)P]KH2PO4 and [(32)P]dihydroxyacetone phosphate ([(32)P]DAP) in the dark were characterized by very high FBP and SBP levels prior to illumination. Metabolism of these pools upon illumination increased with increasing pH of the medium but was consistently inhibited in osmotically stressed chloroplasts. The responses of stromal FBP and SBP pools under hypertonic conditions are discussed in terms of both inhibited light activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) and sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37), and likely increases in stromal ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) active-site concentrations.

Asymptomatic inflammation and/or infection in benign prostatic hyperplasia.

OBJECTIVE: To determine the extent, pattern and clinical significance of asymptomatic histological inflammation and latent infection (National Institute of Health Category IV prostatitis) in benign prostatic hyperplasia (BPH). PATIENTS AND METHODS: The study included 80 patients (from a cohort of 100 consecutive potentially eligible subjects) with a diagnosis of BPH, but no history or symptoms of prostatitis. Histological sections were obtained from specimens collected prospectively at transurethral resection of the prostate (TURP), immunostained for leukocyte common antigen and scanned using a computerized image-analysis system. Foci of inflammation were categorized as glandular, periglandular, stromal or peri-urethral, and the inflammatory cell density graded from 1 to 3. Relationships and correlations were calculated between the volume, degree and type of inflammation, presence and type of bacteria (culture of deep prostatic biopsies), the use of catheters and prostate specific antigen (PSA) levels. RESULTS: Inflammation was identified in all patients but the mean tissue surface area involved was only 1.1% of the total specimen, with periglandular inflammation being the predominant pattern (0.5%). Of the prostate specimens, 44% showed bacterial growth (in 67% of the catheterized patients and 28% of those uncatheterized; 42% of patients were catheterized before TURP). There was no significant difference between any combination of inflammation pattern, volume or grade of inflammation in those catheterized or not (P=0.15) or culture-positive (pathogenic or not) and culture-negative cases (P=0.06). Neither total PSA or PSA density was significantly correlated (P>0.05) with the amount, degree or distribution of inflammation. CONCLUSION: Prostatic inflammation is an extremely common histological finding in patients with symptoms of BPH who have no symptoms of prostatitis. There was no correlation between the degree and pattern of inflammation, catheterization, presence of bacteria, serum PSA or PSA density. The clinical significance of asymptomatic Category IV chronic prostatitis associated with BPH has yet to be determined.