The influence of hydroxyethyl starch on ice formation in aqueous solutions

Differential scanning calorimetry, and, in some supplementary experiments, X-ray diffractometry and cryomicroscopy, were applied to study the influence of concentration (< 70 wt%) and cooling/warming rates (< 320 K/min) on ice formation in aqueous solutions of HES. The calorimetric measurements of the quantity of crystallizing water indicated that a mass fraction ? = 0.522 (i.e., grams water per gram HES) remained unfrozen. These results are in good agreement with our earlier extrapolations from ternary phase diagram data and tend to support the proposed cryoprotective mechanism. The value of ? determined during warming was essentially independent of composition up to the corresponding saturation concentration. It was observed that solutions containing 60 wt% HES or more remained wholly amorphous during cooling even at rates as low as 2.5 K/min (down to 120 K). Such glassy solutions are subject to devitrification at temperatures T_d which depend on the warming rate. The concentrations close to 55 wt% HES mark a transitional range exhibiting two crystallization peaks, probably due to different mechanisms of nucleation, the portion of ice formed during cooling being related to the imposed cooling rate. All samples showed a recrystallization transition at 257.5 K which was also observed cryomicroscopically. Glass transitions, however, could not be detected by the methods applied in this study. The X-ray diffraction patterns contained the structure of only one solid phase, namely hexagonal ice. A comparison of various modifications of HES, PEG, and PVP involving bound water and melting temperature did not reveal marked differences. Minimum initial HES concentrations preventing lethal salt enrichment were computed for both binary and ternary mass fractions of NaCl as biologically relevant parameters, yielding 24.1 and 10.8 wt% HES, respectively.     

Fast sampling,rapid filtration apparatus: Principal characteristics and validation from studies ofd-glucose transport in human jejunal brush-border membrane vesicles

Summary Kinetic data in (brush-border) membrane vesicles which rely on the validity of the initial rate assumption for their interpretation and depend on tracer flux studies using the rapid filtration technique for their experimental measurement have been limited to some extent by the absence of techniques that would allow for real-time data analysis. In this paper, we report on our successful design of a fast sampling, rapid filtration apparatus (FSRFA) which seems to fill up this technical gap since showing the following characteristics: (i) rapid injection (5 msec) and mixing (less than 100 msec) of small amounts of vesicles (10–40 l) with an incubation medium (0.2–1.0 ml); (ii) fast (20 to 80 msec depending on the sample volume) and multiple (up to 18 samples at a maximal rate of 4/sec) sampling of the uptake mixture followed by rapid quenching in the stop solution (approximately 5 msec) according to a predetermined time schedule (any time combination from 0.25 to 9999 sec); and (iii) fast, automated, and sampling-synchronized filtration and washings of the quenched uptake medium (only 15–20 sec are necessary for the first filtration followed by two washings and extra filtrations). As demonstrated using adult human jejunal brush-border membrane vesicles and Na⁺-d-glucose cotransport as models, the FSRFA accurately reproduces the manual aspects of the rapid filtration technique while allowing for very precise initial rate determinations. Moreover, the FSRFA has also been designed to provide as much versatility as possible and, in its present version, allows for a very precise control of the incubation temperature and also permits a few efflux protocols to be performed. Finally, its modular design, which separates the fast sampling unit from the rapid filtration device, should help in extending its use to fields other than transport measurement.     

NMR study of Galeorhinus japonicus myoglobin. 1H-NMR study of molecular structure of the heme cavity

The molecular structure of the active site of myoglobin from the shark, Galeorhinus japonicus, has been studied by 1H-NMR. Some hyperfine-shifted amino acid proton resonances in the met-cyano form of G. japonicus myoglobin have been unambiguously assigned by the combined use of various two-dimensional NMR techniques; they were compared with the corresponding resonances in Physter catodon myoglobin. The orientations of ThrE10 and IleFG5 residues relative to the heme in G. japonicus met-cyano myoglobin were semiquantitatively estimated from the analysis of their shifts using the magnetic susceptibility tensor determined by a method called MATDUHM (magnetic anisotropy tensor determination utilizing heme methyls) [Yamamoto, Y., Nanai, N. & Ch?j?, R. (1990) J. Chem. Soc., Chem. Commun., 1556-1557] and the results were compared with the crystal structure of P. catodon carbonmonoxy myoglobin [Hanson, J. C. & Schoenborn, B. P. (1981) J. Mol. Biol. 153, 117-124]. In spite of a substantial difference in shift between the corresponding amino acid proton resonances for the two proteins, the orientations of these amino acid residues relative to the heme in the active site of both myoglobins were found to be highly alike.     

Bisexual behavior in the male rat: Influence of masculine sexual activity on the display of lordosis behavior

Sexually inexperienced male Wistar rats (strain WI in our colony) known to very infrequently display spontaneous lordosis behavior (Schaeffer et al., 1990b) were used. A first group was tested four times at 5-day intervals for lordosis with vigorous stimulus males (heterotypic sexual behavior), immediately following testing for masculine sexual activity with highly receptive females (homotypic sexual behavior). A small number of animals displayed lordosis during the first test, but more and more animals displayed this behavior from the first to the fourth test. There was no relationship between the degree of masculine sexual activity--intromission without ejaculation or ejaculation--and the occurrence of lordosis behavior. A second group was tested only once for both masculine sexual activity and lordosis behavior as above and afterwards three times at 5-day intervals for lordosis behavior in the absence of any previous testing for masculine sexual activity. A few animals displayed lordosis during their first test. As compared to the first group, the animals which had not displayed lordosis in the first test never showed lordosis responses in the following tests. It is concluded that both homotypic and heterotypic sexual interactions are required for the display of lordosis behavior in the strain of Wistar rats used in this study.     

Observations on the biology of Leuciscus ‘svallize’ in the Kremasta reservoir (Greece)

The age, growth, feeding habits and reproductive biology of Leuciscus svallize in artificial lake Kremasta (Greece), are described. There is a considerable similarity in the feeding and reproductive characteristics between L. svallize and L. cephalus and also a similarity in the life span, growth patterns and age of maturation between L. svallize and some southern L. cephalus populations, which may suggest similar responses of closely related taxa to similar conditions.     

Mutation of asparagine 111 of rubisco from Rhodospirillum rubrum alters the carboxylase/oxygenase specificity.

The conserved asparagine 111 of ribulose-1,5-bisphosphate carboxylase/oxygenase from the photosynthetic bacteria Rhodospirillum rubrum was identified as a candidate for a side-chain that might be involved in the carboxylase/oxygenase specificity. It was replaced by site-directed mutagenesis with aspartic acid, leucine, glutamine or glycine residues. The mutant enzymes exhibit a very low carboxylase activity compared with the wild-type enzyme. The values of Km(RuBP) and kcat for Asn111----Gly, the most active mutant, are 420 microM and 0.034 s-1, compared with 13 microM and 3.0 s-1 for wild-type. The mutation of Asn111----Gly causes a more than tenfold decrease in the CO2/O2 specificity factor, tau, tau Asn111----Gly = 0.56 and tau wild-type = 6.7. This is the first reported change in rubisco specificity by a single site-directed mutation alone and suggests a target for future protein engineering studies.     

Hydration of oligosaccharides: anomalous hydration ability of trehalose.

The disaccharide trehalose extensively exists in anhydrobiotic organism and is considered to play an important role in preserving the integrity of biomembrane. However, the preserving mechanism remains unclear. In this report, we examine the hydration abilities of trehalose and several oligosaccharides composed of alpha-D-glucopyranosyl residues. The unfrozen water fraction per molecule was determined from differential scanning calorimetry measurements of their aqueous solutions. Further, the NMR relaxation time of the natural abundance 17O of water is measured for several saccharide solutions. These results indicate that trehalose has the highest hydration ability among the saccharides studied. In other words, trehalose can effectively lower the mobility of water molecules hydrogen-bonded with saccharides. It is thus reasonable that, among the disaccharides studied, trehalose exhibits the maximum stabilizing effect on the bilayer structure of lipid whose acyl chains are bonded with each other by the apolar interaction, because the apolar interaction is strengthened with the stabilization of the surrounding water structure.     

The R1 gene conferring race-specific resistance to Phytophthora infestans in potato is located on potato chromosome V.

Summary Late blight in potato is caused by the fungusPhytophthora infestans and can inflict severe damage on the potato crop. Resistance toP. infestans is either based on major dominantR genes conferring vertical, race-specific resistance or on minor genes inducing horizontal, unspecific resistance. A dihaploid potato line was identified which carried theR1 gene, conferring vertical resistance to allP. infestans races, with the exception of those homozygous for the recessive virulence allele of the locusV1. The F₁ progeny of a cross between this resistant parent P(R1) and P(r), a line susceptible to all races, was analysed for segregation ofR1 and of restriction fragment length polymorphism (RFLP) markers distributed on the potato RFLP map comprising more than 300 loci. TheR1 locus was mapped to chromosome V in the interval between RFLP markers GP21 and GP179. The map position ofR1 was found to be very similar to the one ofRx2, a dominant locus inducing extreme resistance to potato virus X.     

Delay of Membrane Lipid Degradation by Calcium Treatment during Cabbage Leaf Senescence

Cabbage leaf discs (Brassica oleracea L., Capitata group) were floated adaxial side up in 0, 0.05, or 0.25 m CaCl₂ solutions at 15°C for 14 d in the dark. To assess whether the delay of senescence by calcium treatment involved protection of membrane lipids, chlorophyll and protein content and the lipid composition of the membranes were determined during incubation. Chlorophyll and protein content decreased with time, in correlation with a reduction in the amount of phospholipids. The degree of unsaturation of phospholipids and free fatty acids decreased, whereas the ratio of sterol to phospholipid increased. The proportions of phospholipid classes did not change during senescence. The catabolism of phospholipids was delayed by 0.05 m calcium, but accelerated by 0.25 m, as compared to the untreated control. Based on the levels of the lipid intermediates, phospholipase D, phosphatidic acid phosphatase, lipolytic acyl hydrolase, and lipoxygenase appeared to be involved in the breakdown of phospholipids during senescence. Phospholipase D and phosphatidic acid phosphatase may be directly influenced by calcium. The calcium treatment apparently did not affect the activity of acyl hydrolase. Lipoxygenase, responsible for the peroxidation of the polyunsaturated fatty acids, was probably indirectly influenced by calcium. We conclude that the delay of senescence of cabbage leaf discs by calcium treatment involved protection of membrane lipids from degradation.     

Sequence of a novel HLA-DQB1 allele

The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence data base and have been assigned the accesion number M74842. The name DQB1*0304 has been officially assigned by the WHO Nomenclature Committee in November 1991. This follows the agreed policy that, subject to the conditions stated in the most recent Nomenclature Report (WHO Nomenclature Committee for factors of the HLA system, 1991), names will be assigned to new sequences as they are identified. List of such new names will be published in the following WHO Nomenclature Report.