Transport properties of single-file pores with two conformational states.

Complex facilitative membrane transporters of specific ligands may operate via inner channels subject to conformational transitions. To describe some properties of these systems, we introduce here a kinetic model of coupled transport of two species, L and w, through a two-conformational pore. The basic assumptions of the model are: a) single-file of, at most, n molecules inside the channel; b) each pore state is open to one of the compartments only; c) there is at most only one vacancy per pore; d) inside the channel, a molecule of L occupies the same positions as a molecule of w; and e) there is at most only one molecule of L per pore. We develop a general representation of the kinetic diagram of the model that is formally similar to the one used to describe one-vacancy transport through a one-conformational single-file pore. In many cases of biological importance, L could be a hydrophilic (ionic or nonionic) ligand and w could be water. The model also finds application to describe solute (w) transport under saturation conditions. In this latter case, L would be another solute, or a tracer of w. We derive steady-state expressions for the fluxes of L and w, and for the permeability coefficients. The main results obtained from the analysis of the model are the following. 1) Under the condition of equilibrium of w, the expression derived for the flux of L is formally indistinguishable from the one obtainable from a standard four-state model of ligand transport mediated by a two-conformational transporter. 2) When L is a tracer of w, we can derive an expression for the ratio between the main isotope and tracer permeability coefficients (Pw/Pd). We find that the near-equilibrium permeability ratio satisfies (n - 1) < or = (Pw/Pd)eq < or = n, a result previously derived for the one-conformational, single-file pore for the case that n > or = 2. 3) The kinetic model studied here represents a generalization of the carrier concept. In fact, for the case that n = 1 (corresponding to the classical single-occupancy carrier), the near-equilibrium permeability ratio satisfies 0 < or = (Pw/Pd)eq < or = 1, which is characteristic of a carrier performing exchange-diffusion.     

Electrophysiological characteristics of cardiac pacemaker cells of the frog Caudiverbera caudiverbera

1. The cardiac pacemaker cells of the frog Caudiverbera caudiverbera are centrally located in the sinus venosus. These cells are rounded, smaller than contractile fibres and have large nuclei. 2. Intracellular recording confirmed the existence of primary and transitional pacemaker cells. 3. Action potentials from primary cells were resistant to blockade by tetrodotoxin (TTX), but were abolished by verapamil suggesting that their bioelectric activity is dependent on a slow inward current. 4. Transitional cells appeared to have two different inward currents contributing to the upstroke: a fast TTX-sensitive and a slow verapamil-sensitive current.     

Effect of feeding pattern on the sensitivity of hepatic carnitine palmitoyl-transferase to inhibition by malonyl-CoA in the rat

1. The feeding pattern influences the inhibitory effects of malonyl-CoA on carnitine palmitoyltransferase-I. 2. The sensitivity of liver carnitine palmitoyltransferase-I to malonyl-CoA is increased in rats meal-fed when compared to rats fed ad libitum. 3. Moreover, liver carnitine palmitoyltransferase-I of meal-fed rats remains more sensitive to inhibition by malonyl-CoA during a 24 hour fast than liver carnitine palmitoyltransferase-I of rats previously fed ad libitum.     

Plasma somatostatin-like immunoreactivity during growth-hormone-releasing hormone therapy in non-growth-hormone-deficient children

To date, the effects of long-term growth hormone (GH)-releasing hormone [GHRH(1-29)-NH2] treatment on the plasma concentrations of somatostatin-like immunoreactivity (SLI) remain undefined. In the present study, the effect of GHRH(1-29)-NH2 therapy on plasma SLI levels has been studied in 11 non-GH-deficient children. The pattern of administration was 5 micrograms/kg body weight, given subcutaneously once every day. There was no significant change in plasma SLI levels after bolus injection of GHRH(1-29)-NH2 before and during GHRH(1-29)-NH2 therapy. However, plasma SLI rose in basal plasma and nocturnal sleep after 3 months of GHRH(1-29)-NH2 therapy and remained the same during 6 months of treatment with GHRH(1-29)-NH2. The reason for this finding is uncertain, but an increase in SLI release from the enteroinsular axis is a possible explanation. The association of our findings with the role of the circulating SLI on nutrient homeostasis and the effects of GNRH on growth velocity is discussed.     

Human enzyme polymorphism in the Canary Islands. III. Tenerife Island population

We analyzed the genetic polymorphism of eight red cell enzymes in samples from different geographical areas of Tenerife and the Iberian peninsula. The gene frequency heterogeneity found within the Tenerife samples was at the same level as that of Tenerife-mainland comparisons. The presence of the Negroid G6PD A+ allele in the Tenerife samples is evidence of an African admixture with a mean estimation of 4.5%.     

Detection and quantification of patulin and griseofulvin by high pressure liquid chromatography in different strains of Penicillium griseofulvum Dierckx

Patulin and griseofulvin production by twelve strains ofPenicillium griseofulvum Dierckx, eleven of which were isolated from pistachio (Pistacia vera) nuts and the other was supplied by the Spanish Collection of Type Culture, was investigated. Six strains of the eleven isolated had ability to produce patulin and griseofulvin in Yes medium. All the strains studied had no ability to produce patulin in Wickerham medium. Griseofulvin production was significant in both media but higher in Wickerham. These metabolites were separated and determined in the chloroform extracts of cultures by high performance liquid chromatography with ultraviolet detection. The best conditions were: acetonitrile — water (45∶55) as mobile phase, a flow rate of 2.0 mL/min and a μ Bondapack C₁₈ column.     

Effect of Zeitgeber Intensity Reduction on a Simulated Dual-Oscillator Human Circadian System: Classical and Dynamic Analysis

The two-oscillator model of human circadian rhythmicity was analyzed when a zeitgeber relative intensity of 1, 0.5, or 0.1 was introduced into the equations. Fourier analysis was compared with dynamic analysis such as attractor reconstruction or Liapunov exponent calculation. After a 50 or 90% reduction in zeitgeber intensity, the dynamics of the system became equivalent and differed significantly from those of a system with maximal zeitgeber intensity. When 10% aleatory noise was added to the data, the analysis was still applicable, and the results obtained were essentially the same as in the absence of noise. Dynamic analysis could thus provide a distinct classification for periodic data, based on the type of analysis.     

Expression of two cytochromes P450 involved in carcinogen activation in a human colon cell line

Cytochrome P450 is known to cause carcinogen activation and correspondingly increased cancer risk in animal models. In order to determine whether P450 in the colon may be involved in cancer development in the human, the human colon cell line LS174T was examined for the presence of various cytochromes P450. Two isozymes of P450 were identified in the human cell line. Expression of P450IAl or IA2 was increased by treatment of the cell line with benzanthracene; the induction was demonstrated by an increase in RNA hybridizing to a probe for P4501Al and by ethoxyresorufin deethylation activity. Western analysis of microsomes isolated from human colon tissue also demonstrated the presence of P4501A1, as well as a form which cross-reacted to an antibody to human P450IIC9. Another isozyme, P450IIE1, was identified by polymerase chain reaction amplification of RNA from LS174T cells. These results underscore the presence of cytochromes P450 in colonic tissue and provide a basis for the involvement of isozyme-specific P450 mediated reactions in carcinogenesis of the colon.Some of the data presented here were taken from a thesis submitted by D.K.H. in partial fulfillment of the requirements for the Ph.D. degree in the University of Texas Graduate School of Biomedical Sciences.     

Establishment of transformed root cultures of Perezia cuernavacana producing the sesquiterpene quinone perezone

Summary The sesquiterpene quinone currently known as perezone is abundantly produced by the roots of Perezia cuernavacana. This compound is of biotechnological interest since it may be used as a pigment and has several pharmacological properties. In this work we demonstrate that perezone is also produced in transformed root cultures of P. cuernavacana. Hairy roots were induced by inoculation of internodal segments of sterile plants of P. cuernavacana with Agrobacterium rhizogenes AR12 strain. The axenic liquid MS medium cultures of the hairy roots isolated from the internodes showed active growth in the absence of growth regulators. The transformed nature of the tissue was confirmed by genomic integration (PCR and slot blot hybridization) and expression (enzyme activity) of the marker gus-gene. The production of perezone by a transformed root culture was evidenced by IR spectroscopy. Our results offer an alternative for enhanced production of perezone and represent an advantage over its extraction from natural plant populations which present problems in their agronomic culture.     

Simultaneous high-biomass protein production and nutrient removal using Spirulina maxima in sea water supplemented with anaerobic effluents

Maximum protein accumulation (71%, w/w) and nutrient removal by a mutant strain of Spirulina maxima growing on sea water supplemented with anaerobically treated pig slurry was achieved at 30°C with constant illumination (60 to 70 Em^-2s^-1), using a flow rate of 14.5 cm s^-1 (20 rev. min^-1 of a paddle wheel). Total phosphates were decreased by 99% and all ammonia-N was removed under these conditions.The authors are with the Department of Environmental Biotechnology, Institute of Ecology, Aptd Postal 63, Xalapa, Ver., Mexico