Model of calcium movements during activation in the sarcomere of frog skeletal muscle

A model of calcium movement during activation of frog skeletal muscle is described. The model was based on the half sarcomere of a myofibril and included compartments representing the terminal cisternae, the longitudinal sarcoplasmic reticulum, the extramyofibrillar space, and the myofibrillar space. The calcium-binding proteins troponin, parvalbumin, and calsequestrin were present in appropriate locations and with realistic binding kinetics. During activation a time-dependent permeability in the terminal cisternal wall led to calcium release into the myoplasm and its diffusion through the myoplasm longitudinally and radially was computed. After adjustment of three parameters, the model produced a myoplasmic free-calcium concentration that was very similar to those recorded experimentally with calcium indicators. The model has been used to demonstrate the importance of parvalbumin in the relaxation of skeletal muscle, to describe the time course and magnitude of calcium gradients associated with diffusion across the sarcomere, and to estimate the errors associated with the use of aequorin as an intracellular calcium indicator in muscle.     

Aspects of the mineral nutrition of some native British plants — inter-site variation

Fifteen common native British plants were each sampled at a range of sites in Great Britain and green tissues analysed for several inorganic nutrients. Sampling criteria are discussed. The inter-site variation of each element within a species is assessed as a frequency distribution of raw data. Sample values of parameters including arithmetic mean, variance (coefficient of variation), skewness and kurtosis are presented. Their stability is assessed from nitrogen in sub-samples of Pteridium. This suggested sample sizes were adequate but some distributions had sufficient kurtosis to affect the variance. These parameters showed distinctions between macro- and micro-elements and between species. Some mean values sharply distinguished between species and may help to assess current theories of strategy and adaptation but a wider range of species is needed to clarify trends. Coefficients of variation are discussed and were relatively low for a nation-wide survey after allowing for sampling constraints. Coefficients of skewness and kurtosis showed two-thirds of the sample distributions were non-normal. Ecological aspects of the distributions are discussed and are relevant to studies along environmental gradients. Published hypotheses linking positive skewness to stress in the field are considered and two other postulates discussed. Distribution bounds such as those confining 95% of the values are discussed in relation to possible critical levels of nutrients.Nomenclature follows Clapham et al. (1981), Excursion flora of the British Isles. 3rd ed. University Press, Cambridge, except Chamaenerion.     

Positive effort dependence of maximal expiratory flow

The maximal expiratory-flow volume (MEFV) curve in normal subjects is thought to be relatively effort independent over most of the vital capacity (VC). We studied seven normal males and found positive effort dependence of maximal expiratory flow between 50 and 80% VC in five of them, as demonstrated by standard isovolume pressure-flow (IVPF) curves. We then attempted to distinguish the effects of chest wall conformational changes from possible mechanisms intrinsic to the lungs as an explanation for positive effort dependence. IVPF curves were repeated in four of the subjects who had demonstrated positive effort dependence. Transpulmonary pressure was varied by introducing varied resistances at the mouth but effort, as defined by pleural pressure, was maintained constant. By this method, chest wall conformation at a given volume would be expected to remain the same despite changing transpulmonary pressures. When these four subjects were retested in this way, no increases in flow with increasing transpulmonary pressure were found. In further studies, voluntarily altering the chest wall pattern of emptying (as defined by respiratory inductive plethysmography) did however alter maximal expiratory flows, with transpulmonary pressure maintained constant. We conclude that maximal expiratory flow can increase with effort over a larger portion of the vital capacity than is commonly recognized, and this effort dependence may be the result of changes in central airway mechanical properties that occur in relation to changes in chest wall shape during forced expiration.     

Involvement of organic molybdenum compounds in the interaction between copper, molybdenum, and sulfur

The effect on Cu metabolism of two organic Mo compounds, cysteine-Mo (CM) and cysteine-Mo-S (CMS), and of an inorganic compound, tetrathiomolybdate (TTM), was investigated in sheep. Intravenous administration of CMS or TTM increased total plasma Cu concentrations and promoted the appearance of trichloroacetic acid (TCA)-insoluble Cu in plasma. Plasma Mo was increased by both compounds. Column chromatography of plasma showed that CMS caused the accumulation of TCA-insoluble Cu in high-MW fractions, whereas TTM increased the Cu content of low-MW fractions, mainly albumin. CMS and TTM increased the concentration of Cu and Mo in kidney. In liver, Mo concentrations were elevated by both CMS and TTM, and Cu concentrations were reduced by TTM when it was given at a low dose rate. The subcellular distribution of Cu and Mo in liver and kidney was investigated. The findings are discussed in relation to the proposal that Mo-containing, organic compounds are intermediaries in the interaction between Cu, Mo, and S in ruminants.     

Production of Methyl Ketones from Secondary Alcohols by Cell Suspensions of C2 to C4n-Alkane-Grown Bacteria

Nineteen new C₂ to C₄n-alkane-grown cultures were isolated from lake water from Warinanco Park, Linden, N.J., and from lake and soil samples from Bayway Refinery, Linden, N.J. Fifteen known liquid alkane-utilizing cultures were also found to be able to grow on C₂ to C₄n-alkanes. Cell suspensions of these C₂ to C₄n-alkane-grown bacteria oxidized 2-alcohols (2-propanol, 2-butanol, 2-pentanol, and 2-hexanol) to their corresponding methyl ketones. The product methyl ketones accumulated extracellularly. Cells grown on 1-propanol or 2-propanol oxidized both primary and secondary alcohols. In addition, the activity for production of methyl ketones from secondary alcohols was found in cells grown on either alkanes, alcohols, or alkylamines, indicating that the enzyme(s) responsible for this reaction is constitutive. The optimum conditions for in vivo methyl ketone formation from secondary alcohols were compared among selected strains: Brevibacterium sp. strain CRL56, Nocardia paraffinica ATCC 21198, and Pseudomonas fluorescens NRRL B-1244. The rates for the oxidation of secondary alcohols were linear for the first 3 h of incubation. Among secondary alcohols, 2-propanol and 2-butanol were oxidized at the highest rate. A pH around 8.0 to 9.0 was found to be the optimum for acetone or 2-butanone formation from 2-alcohols. The temperature optimum for the production of acetone or 2-butanone from 2-propanol or 2-butanol was rather high at 60°C, indicating that the enzyme involved in the reaction is relatively thermally stable. Metal-chelating agents inhibit the production of methyl ketones, suggesting the involvement of a metal(s) in the oxidation of secondary alcohols. Secondary alcohol dehydrogenase activity was found in the cell-free soluble fraction; this activity requires a cofactor, specifically NAD. Propane monooxygenase activity was also found in the cell-free soluble fraction. It is a nonspecific enzyme catalyzing both terminal and subterminal oxidation of n-alkanes.     

Anaerobic Degradation of Cyanuric Acid, Cysteine, and Atrazine by a Facultative Anaerobic Bacterium

A facultative anaerobic bacterium that rapidly degrades cyanuric acid (CA) was isolated from the sediment of a stream that received industrial wastewater effluent. CA decomposition was measured throughout the growth cycle by using a high-performance liquid chromatography assay, and the concomitant production of ammonia was also measured. The bacterium used CA or cysteine as a major, if not the sole, carbon and energy source under anaerobic, but not aerobic, conditions in a defined medium. The cell yield was greatly enhanced by the simultaneous presence of cysteine and CA in the medium. Cysteine was preferentially used rather than CA early in the growth cycle, but all of the CA was used without an apparent lag after the cysteine was metabolized. Atrazine was also degraded by this bacterium under anaerobic conditions in a defined medium.     

X-Ray Diffraction Pattern from a Bilayer with Protein Outside

The X-ray diffraction pattern from a lipid bilayer has been reported previously; a series of fairly regularly spaced bands was both predicted and observed. In this note it is predicted that adding protein molecules at one or both surfaces of the bilayer will give rise to a cross-interference effect. For smaller amounts of protein, a more or less obvious ripple will be introduced into the bilayer pattern. The amount of protein, its thickness, and the distance from the bilayer to the protein layer all can be readily estimated from an observed ripple. Deciding whether the protein is all on one side or else distributed on both sides of the bilayer may be more difficult; by carefully recording and measuring the intensity near the center of the pattern one may be able to distinguish between the two possibilities. For larger amounts of protein, there will be more profound changes in the diffraction pattern. The theory developed here is applied in the following paper to a lipid dispersion incubated with cytochrome c and will be applied in a subsequent paper to a bacterial envelope. In an appendix it is shown that the patterns reported previously for several natural membranes do not confirm prediction for a normal, continuous lipid bilayer with all the protein outside. Thus it is doubtful that a structure of this kind is valid for these membranes.