An Na+-stimulated Mg2+-transport system in human red blood cells

The initial rate of net Mg2+ efflux was measured in human red blood cells by atomic absorption. In fresh erythrocytes incubated in Na+,K+-Ringer's medium this rate was 7.3 +/- 2.8 mumol/l cells per h (mean +/- S.D. of 14 subjects) with an energy of activation of 13 200 cal/mol. Cells with total Mg2+ contents ([ Mg]i) ranging from 1.8 to 24 mmol/l cells were prepared by using a modified p-chloromercuribenzenesulphonate method. Mg2+ efflux was strongly stimulated by increases in [Mg]i and in external Na+ concentrations ([ Na]o). A kinetic analysis of Mg2+ efflux as a function of [Mg]i and [Na]o revealed the existence of two components: an Na+-stimulated Mg2+ efflux, which exhibited a Michaelian-like dependence of free internal Mg2+ content (apparent dissociation constant = 2.6 +/- 1.4 mmol/l cells; mean +/- S.D. of six subjects) and on external Na+ concentration (apparent dissociation constant = 20.5 +/- 1.9 mM; mean +/- S.D. of four subjects) and a variable maximal rate ranging from 35 to 370 mumol/l cells per h, and an Na+-independent Mg2+ efflux, which showed a linear dependence on internal Mg2+ content with a rate constant of (6.6 +/- 0.7) X 10(-3) h-1. Fluxes catalyzed by the Na+-stimulated Mg2+ carrier were partially dependent on the ATP content of the cells and completely inhibited by quinidine (IC50 = 50 microM) and by Mn2+ (IC50 = 0.5-1.0 mM).     

A simple automatic dispensing apparatus

A simple dispenser using a 2-ml disposable syringe is described. The range of operation is 0.02–1.5 ml and an unusual accuracy is obtained by employing a new principle for dispensers: the dispensed volume is only a fraction of total tidal flow of fluid in the dispenser.     

Autocatalytic processing of the streptococcal cysteine protease zymogen: processing mechanism and characterization of the autoproteolytic cleavage sites.

The autocatalytic processing of the streptococcal cysteine protease zymogen (proSCP) to active streptococcal cysteine protease (SCP) was investigated in vitro using purified protein from Streptococcus pyogenes strain B220. It was found that the autocatalytic maturation of the zymogen proceeds through the sequential appearance of at least six intermediates, five of which were characterized through a combination of N-terminal sequencing and MS. Intermediates were identified as resulting from cleavages after Lys26, Asn41, Lys101, Ala112, and Lys118. Time-course studies of the proSCP processing gave a sigmoidal activity profile and indicated that proSCP catalyses its own transformation, mainly via an intermolecular processing mechanism. A similar sequential appearance of intermediates was observed when inactive Cys192Ser proSCP was treated with native, enzymatically active SCP, thus demonstrating that the maturation can exclusively proceed by a bimolecular mechanism. It was shown that proSCP, but not mature SCP, immobilized on a Sepharose resin is capable of liberating itself from the column, indicating that the zymogen is also capable of intramolecular processing. In order to test whether the amino acid sequences at the processing sites could be used for developing new, specific substrates, 3-amino benzoic acid octapeptide derivatives based on all five characterized amino acid sequences from the autoprocessing cleavage sites were synthesized and tested for activity. The 3-amino benzoic acid derivatives have kcat/KM values ranging from 1200 to 7700.M-1.s-1, making them very good endopeptidase substrates for SCP.     

Role of the serotoninergic raphe-hippocampus system for the antinocifensive effect of morphine

As revealed in earlier studies, the antinocifensive effect of morphine is brought about, among other things, with involvement of serotoninergic transmission mechanisms. In this context the role of the serotoninergic raphe-hippocampus system has been studied in this paper. Topical microinjections of serotonin into the dorsal hippocampus increased morphine analgesia in a dose-dependent fashion, while application into the striatum had no effect. Morphine injections into the median raphe nucleus in relatively low doses exert an antinocifensive effect which is inhibitable by methysergide. Lysergic acid diethylamide administered into the median raphe nucleus also abolished the effect of morphine in a dose-dependent manner. The results in connection with literature data lend support to the presumed integrative function of the serotoninergic raphe-hippocampus system in the mechanism of antinocifensive action of morphine.     

Culture conflict and coping in a group of aboriginal adolescents

Critical incidents adapted to presentation in picture form were used to investigate responses of Aboriginal adolescents from Elcho Island mission in the Northern Territory of Australia in conflict situations arising from culture contact. These Aboriginal youths are part of a complex environment where choice behaviour is mediated by specific and broader situational characteristics of the social environment. Results showed a relationship between conflict responses and orientation to traditional values and skills, but no apparent relationship between conflict responses and modern value orientation or psychopathology variables. Adolescents who attended high school in Darwin were seen as more mission and academically oriented than locally educated youth. Contrary to expected patterns, males appeared to be less involved in both mission and traditional activities and more restricted by traditional social expectations than were females.     

Delta opioid receptor selectivity induced by conformational constraints in linear enkephalin-related peptides: 1H 400-MHz NMR study and theoretical calculations

Introduction into the structure of the linear hexapeptide DSLET (Tyr-D-Ser-Gly-Phe-Leu-Thr) or DTLET (Tyr-D-Thr-Gly-Phe-Leu-Thr) of tert-butyl groups as constraints different from cyclization leads to a large increase in the selectivity for delta opioid binding site in the case of DSTBULET [Tyr-D-Ser-(OtBu)-Gly-Phe-Leu-Thr] (Ki delta = 6.14 nM; Ki mu = 374 nM) and BUBU [Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr(OtBu)] (Ki delta = 4.68 nM; Ki mu = 475 nM) or a loss of affinity for DTTBULET [Tyr-D-Thr(OtBu)-Gly-Phe-Leu-Thr] (Ki delta = 866 nM; Ki mu = 4500 nM). This puzzling behavior is studied here by 400-MHz 1H NMR spectroscopy in DMSO-d6 solution and by theoretical calculations. When DSLET and DTLET are compared, the reduction in energetically accessible phi and psi angles induced by the tert-butyl group in the D-Ser2 residue decreases the degree of freedom in the N-terminal part of the peptides. For DSTBULET and BUBU, the rigidification of the backbone evidenced by the appearance of the large NOE's of Phe4 NH-Gly3 alpha and Gly3 NH-alpha and by the loss of the C7 folding around the D-Ser2 residue found in DSLET could explain the drastic loss of affinity for mu opioid receptors. In DTTBULET, a large change in the spatial orientation around the D-Thr2 (OtBu) residue forces the aromatic rings far from each other.(ABSTRACT TRUNCATED AT 250 WORDS)