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Biomedical subjects

D Sanders

Publications and source records attributed to D Sanders.

At least 163 records · Page 9Linked to original sources
PubMed1988

Hearing in primary school children in an iodine-deficient population in Chinamhora, Zimbabwe.

Chinamhora, Zimbabwe is an area of known endemic goiter and iodine deficiency. Out of 211 primary school children living in the area who had been recruited for a study of the effects of iodine administration, 121 were randomly selected for audiometric testing. All had normal hearing. One further child already noted to have hearing difficulties was tested and found to have fairly severe bilateral nerve deafness, although this was unlikely to have been due to endemic cretinism. Urine iodine/creatinine ratios in 61 out of the 211 children were mostly in the range 50-100 micrograms/g. There is no general impairment of hearing associated with mild to moderate iodine deficiency in this population.

Adolescent↗
PubMed1987

Purification of the N,N'-dicyclohexylcarbodiimide-binding proteolipid of a higher plant tonoplast H+-ATPase.

The H+-ATPase of Beta vacuolar membrane (tonoplast) comprises at least three functionally distinct subunits of Mr = 67,000, 57,000, and 16,000, respectively (Manolson, M. F., Rea, P. A., and Poole, R. J. (1985) J. Biol. Chem. 260, 12273-12279). The hydrophobic carboxyl reagent N,N'-dicyclohexylcarbodiimide (DCCD) inactivates the enzyme with pseudo-first order kinetics, and the concentration dependence of the reaction indicates that DCCD interacts with a single site on the enzyme to exert its inhibitory effect. The apparent pseudo-first order rate constant (k0) is reciprocally dependent on membrane protein concentration, which is expected if a large fraction of the DCCD partitions into the lipid phase. k0 has a nominal value of 1000 M-1 min-1 at a protein concentration of 250 micrograms/ml, although when phase partitioning is taken into account, the true, protein concentration-independent value of k0 is calculated to be about an order of magnitude lower. [14C]DCCD primarily labels the Mr = 16,000 polypeptide of native tonoplast vesicles. Binding is venturicidin-insensitive and occurs at a rate similar to the rate of enzyme inactivation, implying that inhibition is a direct result of covalent modification of the Mr = 16,000 polypeptide. Labeling of the containing Mr = 8,000 subunit of mitochondrial F0F1-ATPase is, on the other hand, faster by a factor of 5 and totally abolished by venturicidin. These results confirm that the Mr = 16,000 polypeptide which copurifies with tonoplast H+-ATPase activity is a subunit of the enzyme. Most of the DCCD-reactive Mr = 16,000 subunit is extracted from acetone:ethanol-washed tonoplast vesicles by chloroform:methanol. [14C]DCCD bound to the Mr = 16,000 polypeptide is enriched in the chloroform:methanol extract by 5-fold compared with native tonoplast and the specific activity (nmol of [14C]DCCD/mg of protein) can be increased a further 37-fold by chromatography on DEAE-Sephadex. It is concluded that the Mr = 16,000 subunit of the tonoplast H+-ATPase is a proteolipid.

Carbodiimides↗
PubMed1987

Teaching primary health care: some lessons from Zimbabwe.

A new teaching programme for fourth-year medical students in child health in Harare, Zimbabwe is outlined. A 2-week attachment to a rural district-level hospital is intended to orient the students to primary health care and to the practice of clinical medicine in a low resource environment. The attachment has become popular with students and it is hoped that it will improve attitudes of teaching staff in the medical school towards primary health care.

Education, Medical, Undergraduate↗
PubMed1986

The membrane proteins of the methanol-induced peroxisome of Candida boidinii. Initial characterization and generation of monoclonal antibodies.

Peroxisomes are massively induced when methylotrophic yeasts are cultured on methanol as the sole carbon and energy source. An analysis of the protein composition of the peroxisomal membrane and the generation of probes against two peroxisomal membrane proteins (PMPs) have been undertaken. Peroxisomes from Candida boidinii were obtained from sucrose gradients as previously described or from a novel one-step purification of the organelle on a Percoll gradient. The protein composition of the membranes from these two preparations was virtually identical. About 10 proteins comprise nearly all of its protein mass. The most prominent proteins have molecular masses of 120, 100, 47, 31-32 (a triplet), and 20 kDa; significant amounts of alcohol oxidase and dihydroxyacetone synthase, the two abundant matrix proteins, also remain associated with the membrane. Glycosylation of the membrane proteins could not be detected. Exposure of the membrane to chaotropes shows that PMPs 100 and 20 are the most easily removable, whereas PMP 47 appears to be the most tightly associated. Mice were injected with peroxisomal membrane, and hybridoma lines were isolated that produced antibody against PMP 20, PMP 47, and dihydroxyacetone synthase. Indirect immunofluorescence with these monoclonal antibodies confirmed that all three proteins are localized to the peroxisomal cluster. Immunoblotting experiments demonstrated that peroxisomal membrane as well as matrix proteins are induced by methanol.

Antibodies, Monoclonal↗
PubMed1986

Generalized kinetic analysis of ion-driven cotransport systems: II. Random ligand binding as a simple explanation for non-michaelian kinetics.

Solute uptake in many cells is characterized by a series of additive Michaelis-Menten functions. Several explanations for these kinetics have been advanced: unstirred layers, transport across more than one membrane, effects of solute concentration on membrane potential, numerous carrier systems. Although each of these explanations might suffice for individual cases, none provides a comprehensive basis for interpretation of the kinetics. The most common mechanism of solute absorption involves cotransport of solute with a driver ion. A model is developed in which solute and driver ion bind randomly to a membrane-bound carrier which provides a single transmembrane pathway for transport. The kinetic properties of the model are explored with particular reference to its capacity to generate additive Michaelian functions for initial rate measurements of isotopic solute influx. In accord with previous analysis of ordered binding models (Sanders, D., Hansen, U.-P., Gradmann, D., Slayman, C.L. (1984) J. Membrane Biol. 77:123), the conventional assumption that transmembrane transit rate-limits transport has not been applied. Random binding carriers can exhibit single or multiple Michaelian kinetics in response to changing substrate concentration. These kinetics include high affinity/low velocity and low affinity/high velocity phases (so-called "dual isotherms") which are commonly observed in plant cells. Other combinations of the Michaelis parameters can result in cis-(substrate) inhibition. Despite the generality of the random binding scheme and the complexity of the underlying rate equation, a number of predictive and testable features emerge. If external driver ion concentration is saturating, single Michaelian functions always result and increasing internal substrate concentration causes uncompetitive inhibition of transport. Numerical analysis of the model in conditions thought to resemble those in many experiments demonstrates that small relative differences in a few key component rate constants of the carrier reaction cycle are instrumental in generation of dual isotherms. The random binding model makes the important prediction that the contributions of the two isotherms show opposing dependence on external concentration of driver ion as this approaches saturation. In the one case in which this dependence has been examined experimentally, the model provides a good description of the data. Charge translocation characteristics of the carrier can be determined from steady-state kinetic data on the basis of the response of substrate flux to modulation of internal driver ion concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Biological Transport↗
PubMed1985

Steady-state kinetic analysis of an electroenzyme.

Primary active transport of ions through the plasma membranes of plants and fungi is driven by a proton-dependent ATPase, which consists of a membrane-embedded (Mr 104,000) polypeptide, forms a beta-aspartylphosphate intermediate and is blocked by orthovanadate. It can be extracted from cell membranes and reactivated in native lipid micelles or in exogenous phospholipid vesicles. For the fungus Neurospora, vesicle preparations directly display proton-pumping, and can develop membrane potentials (delta psi) of 120 mV or pH differences (delta pH) of 2 units, with a stoichiometry of 1 H+ transported per ATP molecule split. In vivo, the proton pump sustains delta psi values of 150-350 mV (cytoplasm negative) and delta pH values up to 3.5 units (pHi congruent to 7, with pHo = 3.5). Since the total proton-motive force thus can exceed 400 mV, compared with a delta GATP of 500 mV, the stoichiometry must be 1 H+/ATP, with little leeway for neutralizing ions. Kinetic analysis of pump-currents measured during forcing of [ATP]i, pHo, pHi, and delta psi yields three main conclusions: again, the stoichiometry is 1 H+/ATP; energy conversion occurs during transmembrane charge transfer, which therefore is probably the E1 approximately P--E2 X P transition (see Na+,K+-ATPase); protons are strongly dissociated at both membrane surfaces, with pKi congruent to 5.4 versus pHi = 7.2, and pKo congruent to 2.9 versus pHo = 5.8. Considerations of structure and partial-reaction chemistry (by analogy with the Na+,K+-ATPase) suggest a kinetically testable model for the transport mechanism: a sequential, double-gated channel, through which the membrane field is transported across the ion, rather than vice versa.

Adenosine Triphosphatases↗
PubMed1984

Kinetics and pH-dependence of glycine-proton symport in Saccharomyces cerevisiae.

Interactions between intracellular pH (pHi) and H+-coupled transmembrane transport of glycine have been studied by means of 31P-NMR, using both aerobic and 'energy starved' cells of the yeast Saccharomyces cerevisiae. The general features of glycine transport in the yeast strain used (NCYC 239) are similar to those already reported for Saccharomyces carlsbergensis and S. cerevisiae, there being two kinetically distinct glycine uptake systems, with pH-independent K1/2 values near 14 and 0.4mM, respectively, but pH-dependent maximal velocities. Glycine transport itself has no measurable effect on pHi in aerobic cells, and only a marginal effect in energy-starved cells, but changes of pHi, imposed by extracellular addition of butyric acid, strongly influence glycine transport. Indeed, the dependence of glycine influx (in energy-starved cells) upon cytoplasmic H+ concentration appears to be third order, showing Hill slopes of 2.7-3.0. A crucial kinetic role for cytoplasmic pH in glycine transport is further indicated by a proportionality between the decline of flux and the decline of pHi produced by various metabolic inhibitors and uncouplers. Extracellular pH (pHo), by contrast, has only a weak effect on glycine influx, showing a Hill slope of 0.5. The major observations can be accommodated by a simple cyclic carrier scheme, in which 2 or more protons are transported along with glycine, but only one extracellular proton binding site dissociates in the testing range, with a pK near 5.5. The model requires a finite membrane potential, which must be somewhat sensitive to both pHi and pHo, and accommodates the discrepancy between measured net proton flux (one per glycine) and the kinetically required proton flux (two or more per glycine) by shunting through other proton-conducting pathways in the yeast membrane.

Biological Transport↗
PubMed1984

Generalized kinetic analysis of ion-driven cotransport systems: a unified interpretation of selective ionic effects on Michaelis parameters.

A major obstacle to the understanding of gradient-driven transport systems has been their apparently wide kinetic diversity, which has seemed to require a variety of ad hoc mechanisms. Ordinary kinetic analysis, however, has been hampered by one mathematically powerful but physically dubious assumption: that rate limitation occurs in transmembrane transit, so that ligand-binding reactions are at equilibrium. Simple models lacking that assumption turn out to be highly flexible and are able to describe most of the observed kinetic diversity in co- and counter-transport systems. Our "minimal" model of cotransport consists of a single transport loop linking six discrete states of a carrier-type molecule. The state transitions include one transmembrane charge-transport step, and one step each for binding of substrate and cosubstrate (driver ion) at each side of the membrane. The properties of this model are developed by sequential use of realistic experimental simplifications and generalized numerical computations, focussed to create known effects of substrate, driver ion, and membrane potential upon the apparent Michaelis parameters (Jmax, Km) of isotopic substrate influx. Specific behavior of the minimal model depends upon the arrangement of magnitudes of individual reaction constants among the whole set (12) in the loop. Well defined arrangements have been found which permit either increasing membrane potential or increasing external driver-ion selectively to reduce the substrate Km, elevate Jmax, jointly raise both Km and Jmax, or lower Km while raising Jmax. Other arrangements allow rising internal driver ion to act like either a competitive or a noncompetitive inhibitor of entry, or allow internal substrate to shut down ("transinhibit") influx despite large inward driving forces. These findings obviate most postulates of special mechanisms in cotransport: e.g., stoichiometry changes, ion wells, carrier-mediated leakage, and gating - at least as explanations for existing transport kinetic data. They also provide a simple interpretation of certain kinds of homeostatic regulation, and lead to speculation that the observed diversity in cotransport kinetics reflects control-related selection of reaction rate constants, rather than fundamental differences of mechanism.

Biological Transport↗
PubMed1984

Sweet sorrow: the color-shading response in an adult cystic fibrosis population.

Research on the color-shading response on the Rorschach has been limited previously to its use as a predictor of suicide. The theoretical understanding of this response was addressed by some of the major Rorschach authors. Adult cystic fibrosis patients were administered a battery of psychological tests, including the Rorschach. While these patients face a premature death, none of these patients were suicidal. A higher than usual incidence of color-shading responses occurred. Rapaport's hypothesis that the color-shading response is an expression of a simultaneously conflicting emotion, or similar to "sweet sorrow," was suggested as a possible hypothesis.

Adult↗
PubMed1983

Stoichiometry of H+/amino acid cotransport in Neurospora crassa revealed by current-voltage analysis.

Coupling of ions to the uptake of neutral and basic amino acids via a general amino acid transport system (System II), was studied in a mutant of Neurospora crassa (bat mtr) which lacks other transport systems for these solutes. All amino acids tested--including ones bearing no net charge--elicited rapid membrane depolarization, as expected for ion-coupled transport. (Since amino acid transport in Neurospora is not dependent on extracellular Na+ or K+, the associated ion is presumed to be H+.) Although the 14C-labeled amino acid fluxes through System II are largely independent of the identity of the amino acid, the depolarization caused by basic amino acids (L-lysine and L-ornithine) is 60-70% greater than that for neutral amino acids (e.g. L-leucine). This difference is consistent with a constant H+/amino acid stoichiometry of 2, the extra charge for lysine and ornithine being that on the amino acid itself, so that the charge ratio basic:neutral amino acids is 3:2. When actual membrane charge flow associated with amino acid uptake was compared with measured 14C-labeled amino acid influx, ratios of 2.07 charges/mol L-leucine and 3.40 charges/mol L-lysine were obtained, again in accord with a constant translocation stoichiometry of 2H+/amino acid. The advantages of this electrical method for estimating H+/solute stoichiometry in cotransport are discussed in relation to more familiar methods.

Amino Acids↗
PubMed1983

Automated analysis of neuromuscular 'jitter'.

This paper describes an interactive program for real time analysis of the neuromuscular jitter. Two implementations, using different hardware for data acquisition, reflect the modular design and flexibility of the software. Details on the time windows are given as well as the available commands. The program features: (1) immediate feedback of acquired data; (2) optional manual editing of data; (3) simple, yet flexible commands; (4) several plot options of raw or analysed data; (5) database interface.

Action Potentials↗
PubMed1983

Mood, sexuality, hormones and the menstrual cycle. I. Changes in mood and physical state: description of subjects and method.

Mood and physical symptoms through the menstrual cycle were investigated in 55 women with normal ovulatory cycles. One-third had attended a clinic with severe premenstrual syndrome (clinic PMS group); the remainder were volunteers either with a history of PMS (non-clinic PMS group) or without (no PMS group). Each cycle was divided into six hormonally distinct phases on the basis of repeated hormone measurement. Self-ratings of "well-being" reached their maximum in the late follicular phase, declining throughout the luteal half of the cycle. This pattern was pronounced and statistically significant in the "clinic" and "nonclinic PMS" groups. In all three groups, "physical distress" increased during the second half of the cycle to reach a maximum in the late luteal phase. A clear temporal relationship was therefore demonstrated between mood, physical state, and hormonal phases of the cycle. It remains uncertain whether changes in the "clinic" group were extreme forms of a normal pattern or were qualitatively different.

Adult↗
PubMed1983

Mood, sexuality, hormones, and the menstrual cycle. II. Hormone levels and their relationship to the premenstrual syndrome.

In women with premenstrual syndrome, negative changes start soon after ovulation gradually increasing as the corpus luteum develops, and reach a maximum during the last 5 days of the luteal phase. They decline rapidly once menstruation starts, disappearing within one or two days of ovarian steroids reaching baseline levels. Positive moods are at maximum when preovulatory estradiol reaches its peak. A comparison of hormone levels in women with high and low degrees of cyclical mood change showed no difference in progesterone, estradiol, testosterone, or androstenedione.

Adult↗
PubMed1983

Mood, sexuality, hormones, and the menstrual cycle. III. Sexuality and the role of androgens.

Sexual interest and activity at different stages of the menstrual cycle was recorded by 55 women with normal ovulatory cycles. In women with marked cyclical mood change, there was an associated cyclical pattern of sexual feelings. Subjective sexuality independent of mood change, was maximal in the mid-follicular (i.e., postmenstrual) and late luteal (i.e., premenstrual) phases. Sexual activity was maximal in the mid-follicular phase. There was no evidence of a periovulatory increase in sexual interest or activity. Mean testosterone levels were correlated with masturbation frequency but not with sexuality involving the partner. A weak association between testosterone and life style (i.e., in full-time work or a housewife) was also evident.

Adult↗