Theory of lipid bilayer phase transitions as detected by fluorescent probes

Summary We present a quantitative theory that relates the fluorescence intensityvs. temperature (I vs. T) profile of a fluorescent-labeled two-component lipid bilayer to the phase diagram of the bilayer and the partition coefficientK of the fluorophore between fluid and solid phases of the bilayer. We show how the theory can be used to evaluateK from experimentalI vs. T profiles and the appropriate phase diagrams as well as to understand the different shapes ofI vs. T profiles obtained with particular fluorophores and phase diagrams. Using calculatedI vs. T graphs, we discuss the meaning of parameters, such as midpoint of the phase transition and onset and termination of a transition, which are often used to characterize phase transitions on the basis of fluorescence intensityvs. temperature profiles.     

Influence of N and K fertilization and growth temperature on 13C/12C ratios of timothy (Phleum pratense L.)

Summary Measurements have been reported of carbon isotope ratios of timothy grown at different temperatures and with varying nitrogen and potassium supplies. Both total plant tissue and extracted plant tissue have been analyzed. The ¹³C/¹²C ratios were found to vary both with temperature and with nutrient level; the highest values of ¹³C were found under the most optimum growth conditions.     

Cell free synthesis of some storage protein subunits by polyribosomes and RNA isolated from developing seeds of pea (Pisum sativum L.)

Polyribosomes which have template activity in the wheat germ system have been isolated from developing pea seeds. Some of the translation products have identical mobilities to the vicilin and legumin subunits by SDS-PAGE. Certain products were specifically immunoprecipitated with antisera prepared against purified vicilin and legumin fractions. Various RNA fractions including poly A-rich RNA have also been isolated from polyribosomes and shown to direct the synthesis of polyripeptides whose properties are similar to the storage protein subunits. The results are discussed in relationship to other investigations with seed storage protein biosynthesis in vitro.Abbreviations DTT dithiothreitol - SDS-PAGE SDS-polyacrylamide gel electrophoresis - TCA tricarboxylic acid     

Japanese psychotherapeutic systems: On acceptance and responsibility

Summary Pelzel (1977: 299) pointed out in a previous issue of this journal how most psychiatric care in Japan is heavily oriented towards pharmacological intervention and takes place in mental hospitals. Moreover, there has been an increase in the number of beds set aside for psychiatric care (Ikegami 1980). The quiet therapies and traditional EastAsian medicine, though flourishing, are not representative of health care for the majority of the population of Japan today.I believe that a preference for pharmacological intervention in psychiatric care is not surprising in light of the above discussion on somatopsychics and the primacy of group harmony. What is badly wanted now are contemporary anthropological studies on the application of biomedicine in Japan (Long 1980, has made an excellent beginning) to give some perspective to the more esoteric studies already undertaken, to demonstrate cross-cultural differences in the application of biomedicine, and to look for continuities of thinking and behavior across all therapeutic systems in Japan. Only then can we extrapolate from these studies to statements about the relationship of therapeutics to Japanese society at large, and about the recurrent question of pluralistic forms of health care in industrial societies.     

13C nmr studies of aurothioglucose: Ligand exchange and redox disproportionation reactions

¹³C nmr studies of gold thioglucose, AuSTg, and solutions containing added β-1-D-thioglucose, TgSH, have been conducted at PD 7.4 and interpreted in terms of complexation and ligand exchange reactions that are consistent with the known preference of gold(I) for linear two-coordinate structures. The upper limit of the half-life for ligand exchange between 0.25 M Au(STg)₂^? and TgSH at pD 7.4 is 2.2 msec. The ¹³C nmr spectra of various thioglucose derivatives have been assigned. A novel oxidation reduction reaction was discovered that leads to the formation of metallic gold and a product tentatively identified as the sulfinic acid derivative of thioglucose. The presence of sulfinic acid in AuSTg was indicated by the infrared absorption at 1050 cm^?1. The same product was formed by slow hydrolysis of thioglucose disulfide. A mechanism for the formation of the sulfinic acid derivative from AuSTg is proposed.     

Molecular forms of acetylcholinesterase present in the white and grey matter of pig brain

Extraction of the white matter of pig brain with EDTA, lysolecithin or Triton X-100 gave poor yields of soluble acetylcholinesterase although these agents had proved effective at solubilizing the enzyme in the grey matter. This finding, together with the observation that the strong detergent sodium deoxycholate, was needed to solubilize the enzyme, shows that it is more difficult to remove acetylcholinesterase from the white matter of brain than from the grey. This could mean that the enzyme in the white matter is more firmly bound to the membrane than the enzyme in the grey matter.The difference in binding of the enzyme from the two regions of the brain is also reflected in the affinity chromatography experiments which showed a lower recovery for the acetylcholinesterase of white matter compared with the enzyme from grey matter.Starch-block electrophoresis of acetylcholinesterase showed a single negatively charged peak of activity for both the naturally soluble and the deoxycholate solubilized preparations. The presence of only one form on electrophoresis suggests that the molecular species of acetylcholinesterase do not arise from differences in charge.Sucrose density gradient centrifugation of the two preparations from white matter gave a single peak of activity with a sedimentation constant of about 10 S. This corresponds closely to the major species of molecular weight 260,000 detected by gradient gel electrophoresis. Other forms detected in both enzyme preparations by gradient gel electrophoresis were species with molecular weights of 660,000, 180,000, 130,000 and 115,000. The significance of these species in terms of the formation of oligomers is discussed.A comparison was made with the corresponding preparations of acetylcholinesterase from the grey matter and the results showed that acetylcholinesterase from the white and grey matter of pig brain were very similar. The exception to this was the species with a molecular weight of 68,000 which was present in the grey but not the white matter of pig brain.     

Control of amino acid transport in the mammary gland of the pregnant mouse

The regulation of the uptake of the amino acid analog α-aminoisobutyric acid was studied in diced mammary glands from pregnant mice. Stimulation of uptake by insulin was not prevented by inhibitors of protein synthesis; protein synthesis inhibitors decreased uptake by 20%; this response occurred more promptly in insulintreated tissues. Elimination of extracellular amino acids led to a substantial increase in transport which was not abolished by inhibitors of protein synthesis. These results indicate that insulin does not increase amino acid transport in this system by altering synthesis and degradation of transport protein. They are consistent with a model in which the activity of the existing amino acid transport protein is subject to negative feedback regulation from the intracellular amino acid pool.     

A comprehensive examination of protein sequences for evidence of internal gene duplication

Summary We have implemented a routine procedure for screening protein sequences for evidence of intragenic duplications. We tested 163 protein sequences representing 116 superfamilies of unrelated proteins. Twenty superfamilies contain proteins with internal gene duplications. The intragenic duplications detected can be divided into two major types. (1) One or more duplications of all or part of a gene produce a protein with two or several detectable regions of sequence homology. Sequences from 18 superfamilies contained this type of duplication. (2) Repeated reduplication of a small DNA segment can produce a protein that is repetitive over most of its length. Three superfamilies contain such repetitive sequences. We also investigated the limits of detection of ancient duplications using sequences derived by random mutation of a model sequence consisting of ten 10-residue repeats. The original repetitive nature of the sequence was usually detected after 250 point mutations even though the ancestral segment could not be accurately reconstructed.     

Control of amylase biosynthesis and release in the parotid gland of the rat

1. Amylase biosynthesis and release in the rat parotid were studied under various conditions. Incorporation of [(3)H]leucine into amylase, extracted from the tissue by immunoadsorbent, was measured and found to be time-dependent and totally inhibited by the protein synthesis inhibitor puromycin. 2. Adrenaline, at a concentration (10mum) that gave maximum stimulation of release, inhibited [(3)H]leucine incorporation into both total protein and amylase. This effect was reversed by phentolamine. 3. Adrenaline (1mum) and isoproterenol (10mum) stimulated biosynthesis of total protein and amylase. These effects were blocked by propranolol, as were the effects on release. Dibutyryl cyclic AMP (2mm) mimicked the effects of isoproterenol and adrenaline (1mum) on both amylase biosynthesis and release. All the above stimulatory effects on amylase biosynthesis were only observed if the tissue was pretreated with effector before pulse-labelling with [(3)H]leucine. 4. Insulin (625muunits/ml initial concentration, 150muunits/ml final concentration) stimulated incorporation of [(3)H]leucine into total protein and amylase when added to the tissue at the same time as the leucine. 5. Carbamoylcholine (10mum) decreased [(3)H]leucine incorporation into total protein and amylase when both were added to the tissue simultaneously, but this effect was prevented by removal of effector and washing the tissue before addition of [(3)H]leucine. 6. Stimulation of beta-adrenergic receptors increased both amylase release and biosynthesis, but stimulation of alpha-receptors can inhibit biosynthesis without inhibiting release. Cholinergic agents can also inhibit amylase biosynthesis, but stimulate release. Insulin at approximately physiological concentration can increase incorporation of leucine into amylase without stimulating release. The system described therefore provides an excellent model for the further investigation of the mechanisms of these diverse effects.     

Lipochondria and the light response of Aplysia giant neurons

The ultrastructure, absorbance, and elemental content of lipochondria present in the cytoplasm of Aplysia giant neurons have been investigated before and after 30–1,200 sec doses of white light at intensities which produce saturated light responses. The effects of exposure to the calcium ionophore A-23187 and to EGTA were also examined. The lipochondria of nonilluminated neurons are membrane-bound, and contain lipids, protein, Na, K, Mg, Ca, Si, Cl, Br, P, and a pigment which is probably β-carotene. The cytoplasm appeared to have little pigment. When neurons were illuminated for 20 min, 60–70% of the lipochondria showed marked ultrastructural alterations, the most notable being the appearance of membranous material. Earlier changes which occur after 30 sec of illumination include the appearance of paracrystalline arrays and mottling. Less than 10% of lipochondria in nonilluminated neurons have a similar appearance. These effects were greatly enhanced in illuminated neurons exposed to the calcium ionophore or EGTA. In nonilluminated neurons, the ionophore also produced ultrastructural changes. In frozen specimens, the calcium content of the most electron dense lipochondria of illuminated neurons was reduced. Other elements which were counted were also reduced. The lipochondria are the main intracellular site of photopigment. They may also act as an intracellular source for calcium which, as the accompanying paper indicated, may mediate phototransduction in Aplysia neurons.