A new mutant class of soybean lacks urease in leaves but not in leaf-derived callus or in roots

Summary We reported earlier the recovery of two classes of soybean urease mutants in soybean (Glycine max L. Merr. cv. Williams). Class I mutants lack the embryo-specific urease while class II mutants lack the activities of both urease isozymes, the embryo-specific and the ubiquitous urease, the latter found in all tissues examined. We report here the recovery of a true-breeding mutant, aj3, which represents the third phenotypic class: normal levels of embryo-specific urease and little or no ubiquitous urease. Unlike class II mutant plants which lack urease in all tissue, aj3 lacks urease activity only in leaves (ca. 2% normal activity); its roots have near normal urease activity. Callus derived from leaves of aj3 has 14% to 40% the urease activity of Williams 82 callus. This partial reduction in urease activity in aj3 callus is sufficient to reduce growth with urea as sole nitrogen source and to confer resistance to 50 mM urea added to callus maintenance medium. Leaves of aj3 produce more than 40 times the urease antigen expected from their urease activity. The aj3 trait is due to a single recessive lesion which is not allelic with lesions at theEu2, Eu3 (class II) orEu1 (class I) loci. We designate the aj3 genotype aseu4/eu4.     

An assessment of the behavioral toxicity of high-energy iron particles compared to other qualities of radiation

Conditioned taste aversion was used to evaluate the behavioral toxicity of exposure to high-energy iron particles (56Fe, 600 MeV/amu) in comparison to that of gamma photons (60Co), high-energy electrons, or fission neutrons. Exposure to high-energy iron particles (5-500 cGy) produced a dose-dependent taste aversion with a maximal effect achieved with a dose of 30 cGy. Gamma photons and electrons were the least effective stimuli for producing a conditioned taste aversion, with a maximal aversion obtained only after exposure to 500 cGy, while the effectiveness of fission neutrons was intermediate to that of photons and iron particles, and a maximal aversion was obtained with a dose of 100 cGy. In the second experiment, rats with lesions of the area postrema were exposed to iron particles (30 cGy), but failed to acquire a taste aversion. The results indicate that (1) high-energy iron particles are more toxic than other qualities of radiation and (2) similar mechanisms mediate the behavioral toxicity of gamma photons and high-energy iron particles.     

Mitochondrial acetyl-CoA carboxylase. Time course of mobilization/activation in liver of refed rats.

Fasted (48 h) rats were killed at 0, 2, 4, 6, 8, 12, 16, 20 and 24 h after they were refed on a high-carbohydrate diet. An increase in the maximal activity and quantity of cystolic acetyl-CoA carboxylase was found in liver of refed rats after a lag time of about 8 h. The increased quantity of cytosolic enzyme was attributable primarily to mobilization of mitochondrial storage forms and not to substantial increase in the rate of synthesis of acetyl-CoA carboxylase.     

Nature of forces stabilizing the transmembrane protein bacteriorhodopsin in purple membrane

Analysis of the far-ultraviolet solution and the oriented-film circular dichroic (CD) spectra of the purple membrane (PM) has indicated that the α-helical segments of its sole protein bacteriorhodopsin (bR) can undergo a significant tilting from the normal to the membrane plane during light-dependent hydroxylamine-mediated bleaching of the bR. However, this drastic change in tertiary structure is free of any observable secondary structural changes. This phenomenon can provide an excellent means for studying the relative contributions of forces responsible for the stability of this transmembrane protein within the membrane bilayer. Perturbation of the PM by varying degrees of papain digestion (resulting in changes in the bR ranging from only an elimination of the long COOH-terminal tail to the additional eliminations of the short NH₂-terminal tail and a number of linkage amino acids between the helical segments of the bR) and by chemical cross-linking with dimethyl adipimidate (resulting primarily in the formation of intramolecular cross-links) resulted in a significant increase in this bleaching-induced tilting in all cases except the one in which only the COOH-tail was eliminated. The most severe perturbation (2-wk papain digestion) increased the net tilt angle per segment from 24 to 39° with no indication of any secondary structural changes. Although these perturbations drastically reduced the structural stability of the bR to bleaching, they caused virtually no observable changes in the intramolecular structure of the bR or the supramolecular structure of the PM based on analysis of extensive absorption, linear dichroic, and CD spectra. In addition, study of the bleaching rates for the perturbed PM samples indicated that a linear correlation exists between the calculated initial bleaching rates and the net tilt angles.

Considering the forces generally assumed to account for the stability of transmembrane proteins in membranes, (a) intersegmental hydrogen bonding and electrostatic interactions, (b) electrostatic interactions between hydrophilic polypeptide segments extending outside the bilayer and the many charged lipid heads of the bilayer, and (c) hydrophobic interactions, it is clear that the results of the bleaching experiments eliminate all but perhaps the last as contributing significantly to the bR stability in the PM. Furthermore, they provide more compelling evidence than previously available that the bR is capable of undergoing relatively large retinyldiene-controlled tertiary structural changes and that the chromophoric retinal serves as the most important factor in the native bR structural stability. This dynamic view of the bR bears directly on models proposed for bR function, favoring those in which protein structural metastability, rather than rigidity, is an essential factor. The proteinquake or deformation wave model proposed by this laboratory falls into this category.

     

Molecular dynamics of antitumor ether-linked phospholipids in model membranes: a spin-label study

We have synthesized a spin-labeled derivative of ET-18-OCH3, a known antitumor ether-linked phospholipid. The spin-labeled analog was shown to be as potent as ET-18-OCH3 in inhibiting 3H-thymidine uptake of HL60 leukemic cells. Electron spin resonance (ESR) studies showed that the mobility of this ether-linked phospholipid in the membrane is more restricted when compared to its ester-linked counterparts. It is probable that the absence of the bulky carbonyl oxygens allows closer packing of the two alkyl chains in the ether-linked phospholipid, thereby reducing the angular amplitude of the motion of the alkyl chains. These findings may be of importance in elucidating mechanisms by which the antitumor ether-linked phospholipids perturb the structure of cellular membranes.     

Neuropeptide Y mobilizes intracellular Ca2+ and increases inositol phosphate production in human erythroleukemia cells

The intracellular concentration of free Ca2+ was monitored by measuring the fluorescence of fura-2 loaded Human Erythroleukemia Cells. Neuropeptide Y (NPY) increased intracellular Ca2+ in a dose-dependent manner and the 50% effective concentration was 2 nM. Chelation of extracellular Ca2+ by EGTA did not reduce the NPY-mediated increase in cytoplasmic Ca2+, indicating that the increase in fluorescence was due to the release of intracellular Ca2+. A second dose of NPY, after intracellular Ca2+ had returned to basal levels, failed to elicit a response, indicating that the NPY receptor had undergone desensitization. In similar experiments, NPY increased the formation of inositol phosphates, suggesting that the mobilization of Ca2+ from intracellular stores in HEL cells was secondary to the generation of inositol phosphates and stimulation of phospholipase C.     

Experimental evaluation of a minnow trap for small lotic fish

A minnow trap that operates in various flow regimes in streams and allows sampling of small fish from stream bed microhabitats was developed. In laboratory and field tests, the most efficient trap design for capturing and retaining various species of fish had one funnel oriented downstream, a plexiglass body, and commercial trout food as bait. These lightweight traps can be set in a wide range of current velocities and depths, and can be useful in investigations that examine the microhabitat use, diel activity patterns or population densities of small lotic fish. Guidelines for the trap's use and for quick verification of capture success in new situations are suggested.     

Effect of inhalation of insecticide spray on learning and memory in rats

Acute exposure to insecticide (Baygon-spray; 5 ml/animal/5 min) inhalation in rats did not affect the learning process but produced a significant loss of memory (P less than 0.01 less than 0.001) whereas chronic exposure (one exposure per day for three weeks) produced a significant delay in learning (P less than 0.05) and memory (P less than 0.01). Acetylcholinesterase activity in brain after acute and chronic exposure declined significantly (P less than 0.01) during the learning process but returned to normal after 24 hr.