Studies on cytosolic guanylate cyclase from human placenta.

We have purified the soluble form of guanylate cyclase from human placenta greater than 2400-fold. The enzyme shared several characteristics with the enzyme purified from other sources including molecular mass and subunit composition, activation by divalent cations, inhibition by ATP and Michaelis constants. The enzyme, however, had a lower absorption maximum in the Soret region (417 +/- 1 nm) than the enzyme from other sources and was activated only one-fifth as much by nitric oxide as the bovine lung enzyme. It appears that the heme prosthetic group in the human placental enzyme may be hexa-coordinate and in the bovine lung enzyme the heme group may be penta-coordinate.     

Stratification of density in dry deciduous forest using satellite remote sensing digital data—An approach based on spectral indices

Forest density expressing the stocking status constitutes the major stand physiognomic parameter of Indian forest. Density and age are often taken as surrogate to structural and compositional changes that occur with the forest succession. Satellite remote sensing spectral response is reported to provide information on structure and composition of forest stands. The various vegetation indices are also correlated with forest canopy closure. The paper presents a three way crown density model utilizing the vegetation indices viz., advanced vegetation index, bare soil index and canopy shadow index for classification of forest crown density. The crop and water classes which could not be delineated by the model were finally masked from normalized difference vegetation index and TM band 7 respectively. The rule based approach has been implemented for land use and forest density classification. The broad land cover classification accuracy has been found to be 91.5%. In the higher forest density classes the classification accuracy ranged between 93 and 95%, whereas in the lower density classes it was found to be between 82 and 85%.     

Platelet calcium pump activity in essential hypertensives and their first-degree relatives

Intracellular free Ca²⁺ concentration has been shown to be elevated in platelets of patients with essential hypertension. This study was designed to characterize Ca²⁺-pump activity of the platelet membranes (surface and intracellular) in these patients. A double-blind study was carried out. Untreated and treated (on R-blockers) essential hypertensives were studied in comparison with normotensive control subjects. First degree blood relatives of essential hypertensives were also studied. The Ca²⁺-activation kinetics of the enzyme showed a significant decrease in the V_max. (for the plasma- and intracellular membranes) and Km (for the intracellular membranes) in the essential hypertensive patients. Increased platelet membrane cholesterol content was observed in these patients. Lowered Ca²⁺-efflux by Ca²⁺-ATPase may lead to elevated intracellular free Ca²⁺-levels in platelets of essential hypertensives. A lowered Ca²⁺-ATPase activity may emerge as a marker for essential hypertension.     

Role of purine metabolism in thidiazuron-induced somatic embryogenesis of geranium (Pelargonium × hortorum) hypocotyl cultures

Somatic embryogenesis in geranium ( Pelargonium × hortorum Bailey cv. Scarlet Orbit Improved) was achieved by culturing hypocotyl sections on Murashige and Skoog (1962) (MS) medium containing 10 μ M thidiazuron (TDZ) (induction medium) for 3 days and subsequently transferring the sections onto a basal medium lacking any plant growth regulators (expression medium). Addition of the purine analogue 2.6-diaminopurine (DAP) to the somatic embryo induction medium completely inhibited the embryogenic response as well as chlorophyll accumulation without affecting enlargement of the treated tissues. Addition of 20 μ M adenine sulphate to the expression medium, i.e during embryo growth and development phase, completely reversed the DAP-induced inhibition of the embryogenic response while addition during the induction phase caused only a 50% reversal of the inhibition. Analysis of endogenous levels of plant growth substances indicated that TDZ alone elevated the levels of auxins, cy-tokinins and abscisic acid while the presence of DAP during the induction phase caused a further increase in the levels of adenine and adenosine. These findings indicate a possible critical role for purines in embryogenesis from geranium hypocotyl tissues. However, the conversion of cytokinin bases to their corresponding nucleotide forms was not evident as the levels of isopentenyl adenine and zeatin increased during the second day of culture.     

Poloxamer 188 decreases susceptibility of artificial lipid membranes to electroporation.

The effect of a nontoxic, nonionic block co-polymeric surface active agent, poloxamer 188, on electroporation of artificial lipid membranes made of azolectin, was investigated. Two different experimental protocols were used in our study: charge pulse and voltage clamp. For the charge pulse protocol, membranes were pulsed with a 10-micronsecond rectangular voltage waveform, after which membrane voltage decay was observed through an external 1-M omega resistance. For the voltage clamp protocol the membranes were pulsed with a waveform that consisted of an initial 10-microsecond rectangular phase, followed by a negative sloped ramp that decayed to zero in the subsequent 500 microseconds. Several parameters characterizing the electroporation process were measured and compared for the control membranes and membranes treated with 1.0 mM poloxamer 188. For both the charge pulse and voltage clamp experiments, the threshold voltage (amplitude of initial rectangular phase) and latency time (time elapsed between the end of rectangular phase and the onset of membrane electroporation) were measured. Membrane conductance (measured 200 microseconds after the initial rectangular phase) and rise time (tr; the time required for the porated membrane to reach a certain conductance value) were also determined for the voltage clamp experiments, and postelectroporation time constant (PE tau; the time constant for transmembrane voltage decay after onset of electroporation) for the charge pulse experiments. The charge pulse experiments were performed on 23 membranes with 10 control and 13 poloxamer-treated membranes, and voltage pulse experiments on 49 membranes with 26 control and 23 poloxamer-treated membranes. For both charge pulse and voltage clamp experiments, poloxamer 188-treated membranes exhibited a statistically higher threshold voltage (p = 0.1 and p = 0.06, respectively), and longer latency time (p = 0.04 and p = 0.05, respectively). Also, poloxamer 188-treated membranes were found to have a relatively lower conductance (p = 0.001), longer time required for the porated membrane to reach a certain conductance value (p = 0.05), and longer postelectroporation time constant (p = 0.005). Furthermore, addition of poloxamer 188 was found to reduce the membrane capacitance by approximately 4-8% in 5 min. These findings suggest that poloxamer 188 adsorbs into the lipid bilayers, thereby decreasing their susceptibility to electroporation.     

Protective effects of lazaroids against oxygen-free radicals induced lysosomal damage

Lipid peroxidation of membranes by oxygen free radicals has been implicated in various disease states. Different antioxidants and iron chelators have been used to reduce lipid peroxidation. Lazaroids have been used for the acute treatment of central nervous system disorders such as trauma and ischemia wherein lipid peroxidative processes take place.In this study we evaluated the effect of lazaroids (U-785 18F and U-74389F) on the release of acid phosphatase activity and formation of malondialdehyde (MDA) in rat liver lyosomes subjected to exogenously generated oxygen free radicals. There was a significant increase in the acid phosphatase release and MDA formation in the presence of oxygen free radicals. This was prevented by both the lazaroids. In a separate study the effect of lazaroid U-74389F was seen on the zymosan-stimulated polymorphonuclear (PMN) leukocyte-derived chemiluminescence. The PMN leukocyte chemiluminescent activity was attenuated by the lazaroid in a dose-dependent manner. These studies suggest that lazaroids may inhibit lipid peroxidation and stabilize the membrane.     

Transport of bacteria in porous media: II. A model for convective Transport and growth

A model is presented for the coupled processes of bacterial growth and convective transport of bacteria has been modeled using a fractional flow approach. The various mechanisms of bacteria retention can be incorporated into the model through selection of an appropriate shape of the fractional flow curve. Permeability reduction due to pore plugging by bacteria was simulated using the effective medium theory. In porous media, the rates of transport and growth of bacteria, the generation of metabolic products, and the consumption of nutrients are strongly coupled processes. Consequently, the set of governing conservation equations form a set of coupled, nonlinear partial differential equations that were solved numerically. Reasonably good agreement between the model and experimental data has been obtained indicating that the physical processes incorporated in the model are adequate. The model has been used to predict the in situ transport and growth of bacteria, nutrient consumption, and metabolite production. It can be particularly useful in simulating laboratory experiments and in scaling microbial-enhanced oil recovery or bioremediation processes to the field. (c) 1994 John Wiley & Sons, Inc.     

Characterization and Plasmid Profile of Xanthomonas campestris pv. Glycines from Maharashtra, India

Xanthomonas campestris pv. glycines , (Xcg), the causative agent of the bacterial pustule disease of soybean was isolated and characterized. On susceptible soybean the pathogenic isolates displayed characteristic chlorotic lesions around the site of infection within 48 h of inoculation. The pathogenic isolates were found to contain two cryptic plasmids. A smaller plasmid of 1.5 kb and a larger one of size about 25 kb. SDS-PAGE profile of the soluble proteins of the pathogenic isolatess, howed a different pattern compared to that of the non-pathogenic isolates.