The kinetics of algal photoadaptation in the context of vertical mixing

The responses of phytoplankton to turbulent motions in the surfacemixed layer can be measured to estimate the rate of verticalmixing. If the time scale for the response (photoadaptation)is shorter than that for vertical mixing, phytoplankton willexhibit a vertical gradient associated with adaptation to ambientlight, whereas if mixing occurs with a time scale shorter thanthat of photoadaptation, the surface mixed layer will be uniformwith respect to the photoadaptive parameter. To examine thephysiological bases for a model of vertical mixing and photoadaptation,we grew the marine diatom Thalassiosira pseudonana (clone 3H)at three photon flux densities and subjected the cultures toreciprocal light shifts, measuring physiological and chemicalchanges over the following 10 h. Several parameters, easilymeasured in nature and attributable primarily to phytoplankton,responded to fluctuating light on different time scales. Aftercultures were exposed to relatively bright light, both the initialslope of the photosynthesis-irradiance curve and in vivo fluorescencewere depressed on a time scale of less than an hour. Photosyntheticcapacity was also reduced transiently, but recovered over manyhours to a high level characteristic of an adapted state. First-orderkinetics (the current model of choice for describing photoadaptation)reasonably described the rapid responses of phytoplankton tobright light, but other parameters (i.e. cellular chemical compositionand photosynthetic capacity) changed as a result of unbalancedgrowth and required much longer to adapt from low to high lightas compared to from high to low light. A logistic model of thisadaptation is presented. The model suggests that hysteresisof adaptation during vertical mixing may have important consequences.The vertical distributions of photoadaptive properties in mixedlayers not only reveal the rate of vertical mixing, but showhow phytoplankton integrate environmental fluctuations.     

Chronic exposure to ELF fields may induce depression

Exposure to extremely-low-frequency (ELF) electric or magnetic fields has been postulated as a potentially contributing factor in depression. Epidemiologic studies have yielded positive correlations between magnetic- and/or electric-field strengths in local environments and the incidence of depression-related suicide. Chronic exposure to ELF electric or magnetic fields can disrupt normal circadian rhythms in rat pineal serotonin-N-acetyltransferase activity as well as in serotonin and melatonin concentrations. Such disruptions in the circadian rhythmicity of pineal melatonin secretion have been associated with certain depressive disorders in human beings. In the rat, ELF fields may interfere with tonic aspects of neuronal input to the pineal gland, giving rise to what may be termed "functional pinealectomy." If long-term exposure to ELF fields causes pineal dysfunction in human beings as it does in the rat, such dysfunction may contribute to the onset of depression or may exacerbate existing depressive disorders.     

Interaction of the antioestrogen ICI 164,384 with the oestrogen receptor

The use of partially purified preparations of the human uterine oestrogen receptor has enabled, for the first time, a study of the binding of the steroidal, pure antioestrogen ICI 164,384 [N-n-butyl-11-(3,17 beta-dihydroxy-oestra-1,3,5(10)-trien-7 alpha-yl)N-methyl-undecamide] to the oestrogen receptor. Scatchard analyses of the binding of [3H]oestradiol and [3H]ICI 164,384 to the receptor show that the equilibrium dissociation constants for the interactions of these ligands with the receptor at 0 degrees C are 0.44 and 0.69 nM respectively. The concentration of receptor binding sites for the agonist was 1986 fmol/mg protein whilst that for the antagonist was 1400 fmol/mg protein. The affinity of the antioestrogen-receptor complex for DNA-cellulose does not increase following exposure to conditions that transform the oestrogen-receptor complex.     

Viral gene inhibition of class I major histocompatibility antigen expression: not a general mechanism governing the tumorigenicity of adenovirus type 2-, adenovirus type 12-, and simian virus 40-transformed Syrian hamster cells

The association between the level of class I major histocompatibility (MHC) antigen expression and the tumorigenic phenotype was determined for cells from a series of 15 lines of adenovirus type 2 (Ad2)-, Ad12-, and simian virus 40 (SV40)-transformed hamster cells and 16 lines of cells established from hamster tumors induced by SV40 mutants. These cells range from nontumorigenic to highly tumorigenic in both syngeneic and allogeneic adult hamsters. The Ad2-transformed cells--cells that were nontumorigenic in syngeneic adult hamsters--expressed either high levels or low levels of class I MHC antigens. The SV40-transformed cells--cells transformed in vitro that produced tumors with equal efficiency in both syngeneic and allogeneic adult hamsters--or cells derived from SV40-induced tumors expressed very high levels of class I MHC antigens. The Ad12-transformed cells uniformly expressed low levels of class I MHC antigens; these cells produced tumors 200- to 1,000-fold less efficiently in allogeneic adult hamsters than in syngeneic adult hamsters and produced tumors with about the same efficiency in immunoimmature newborns and immunocompetent syngeneic adult hamsters. We conclude that the expression of either high levels or low levels of class I MHC antigens is, at most, a minor factor in the differences observed among these adenovirus- and SV40-transformed cells in their tumor-inducing capacity in naive, immunocompetent hamsters.     

The microbial environment and intestinal nematode infections of Heligmosomoides polygyrus in laboratory mice

The difficulty of establishing primary infections of Heligmosomoides polygyrus (= Nematospiroides dubius) in ASH/CSI mice in the Laboratory Animal House at Royal Holloway and Bedford New College during a recent autumn and spring period was associated with a syndrome of worm distortion, together with zero or low worm establishment and reduced fecundity (eggs/female worm). The eggs produced were non-viable and the egg capsule comprised a rumpled lipid and ruptured chitin layer. The egg size and peaks of egg production were also reduced and the total egg output ceased entirely by day 28 post-infection in male mice. The syndrome was repeated when control LACA mice harbouring 'normal' infections of H. polygyrus were housed on the same source of peat bedding material as the ASH/CSI mice. An increase in H. polygyrus egg production in ASH/CSI mice, removed from the peat or treated with 0.04% oxytetracycline hydrochloride suggested that the cause of the syndrome was microbial in origin. A microbiological assay of the peat, which was the common denominator of all syndrome infections, revealed an abundance of chitinase secreting species of bacteria (Bacillaceae). Bacterial chitinase was therefore likely to rupture the chitin layer of the egg capsule producing nonviable eggs and either abnormal or no larvae. Preliminary in vitro studies using chitinase from Streptomyces griseus indicated that the hatching success of eggs of H. polygyrus was reduced as the concentration of chitinase increased.     

Cytochrome c: ion binding and redox properties. Studies on ferri and ferro forms of horse, bovine, and tuna cytochrome c

The ion binding properties of horse, bovine, and tuna cytochrome c (both oxidized and reduced) have been measured using a combination of ultrafiltration, neutron activation, and ion chromatography. The ions investigated were chloride, phosphate, and Tris-cacodylate. Ion chromatography and neutron activation analysis techniques were employed to determine the concentration of free anions. Binding constants are obtained from modified Scatchard plots (in the range of 10-2000 M-1). The redox potentials for cytochrome c at different ionic strengths, pH 7.0, have been determined. In this paper we report the ionic strength and ion binding effects on the redox properties of horse, bovine, and tuna cytochrome c. Potential versus ionic strength dependence for horse, bovine, and tuna cytochrome c from the experimental data were compared with a theoretical model.     

Integration of membrane proteins into the endoplasmic reticulum requires GTP

We have examined the requirement for ribonucleotides and ribonucleotide triphosphate hydrolysis during early events in the membrane integration of two membrane proteins: the G protein of vesicular stomatitis virus and the hemagglutinin-neuraminidase (HN) glycoprotein of Newcastle disease virus. Both proteins contain a single transmembrane-spanning segment but are integrated in the membrane with opposite orientations. The G protein has an amino-terminal signal sequence and a stop-transfer sequence located near the carboxy terminus. The HN glycoprotein has a single sequence near the amino terminus that functions as both a signal-sequence and a transmembrane-spanning segment. Membrane insertion was explored using a cell-free system directed by transcribed mRNAs encoding amino-terminal segments of the two proteins. Ribosome-bound nascent polypeptides were assembled, ribonucleotides were removed by gel filtration chromatography, and the ribosomes were incubated with microsomal membranes under conditions of defined ribonucleotide content. Nascent chain insertion into the membrane required the presence of both the signal recognition particle and a functional signal recognition particle receptor. In the absence of ribonucleotides, insertion of nascent membrane proteins was not detected. GTP or nonhydrolyzable GTP analogues promoted efficient insertion, while ATP was comparatively ineffective. Surprisingly, the majority of the HN nascent chain remained ribosome associated after puromycin treatment. Ribosome-associated HN nascent chains remained competent for membrane insertion, while free HN chains were not competent. We conclude that a GTP binding protein performs an essential function during ribosome-dependent insertion of membrane proteins into the endoplasmic reticulum that is unrelated to protein synthesis.     

MPTP in mice: treatment, distribution and possible source of contamination

Mice were treated daily with [3H]MPTP (30 mg/kg, 1 uCi, s.c.) for 1, 3, and 10 days to determine the fate and localization of tritiated compounds. An untreated mouse was housed either in the same cage ("cage-mate control") or in an adjacent cage separated by mesh-wire ("near-neighbor control"). The radioactivity measured in blood, brain, liver, and remaining body of [3H]MPTP-treated mice was dependent on the total dose of the drug the animals received and did not vary with the type of tissue analyzed. Significant amounts of radioactivity were found in the tissues of the "cage-mate control" mice, but not of the "near-neighbor control" mice. The route of transmission appears to be through the urine, as the urine of [3H]MPTP-treated mice was highly radioactive after the drug injection. Only traces of radioactivity were found in their feces and there was no increase in the background radiation in the environment of the cages, indicating that the tritiated compounds were not exhaled. Proper disposal of urinary products of MPTP-treated animals is therefore necessary to reduce the risk of possible drug contamination in humans.     

Reconstruction of the burned palm: full-thickness versus split-thickness skin grafts--long-term follow-up

The long-term results of full-thickness (N = 11) and split-thickness (N = 14) skin grafts for reconstitution of the palmar surface following release of palmar burn scar contractures in pediatric patients are compared. Patients treated with full-thickness skin grafts required 1.2 +/- 0.4 operations (mean +/- SD). Patients treated with split-thickness skin grafts required 1.3 +/- 0.6 operations (mean +/- SD). No significant difference in the number of operative procedures was noted. No functional difference existed between the two groups. The use of split-thickness skin grafts provided comparable function without increased operative procedures and was less deforming. Increased use of split-thickness skin grafts following release of palmar burn scar contractures in pediatric patients should be considered.