Abstract Not Available.

Abstract Not Available.

Abstract Not Available.

The artificial transmutation of the gene is an old problem. Investigators tried to produce mutations artificially, but failed until 1927 when Muller announced that gene mutations could be produced by means of X-rays. This suggested to his contemporaries the use of other agencies for this purpose. Since his announcement, other agencies that have experimentally been proved to produce a positive effect are, in their chronological order: beta and gamma radiation and ultra-violet light. In the production of mutations by X-rays, Muller, in 1927, showed that a heavy treatment caused a rise of approximately fifteen thousand percent in the mutation rate over that in the untreated cells. The effects of radium in producing mutations was shown by Hanson and Heys in 1928. They found that when adult flies were treated six hours with 140 milligrams of radium the percentage of lethal mutations produced was 8.2. When the beta rays were absorbed by a lead screen the gamma rays produced 2.8 percent of lethal mutations. The alpha-rays were absorbed by the walls of the needles which contained the source of radium. In 1928 Stadler found three mutations in radium-radiated barley seedlings out of 1,039 head progeny that he examined. In 1933 Altenburg succeeded in producing lethal mutations in Drosophila by irradiating eggs with u1tra-violet light. He reported the production of eight lethal mutations in 108 treated males, and showed that these mutations must have occurred during an interval of less than an hour at the time of raying. Since the occurrence of such a large percentage of lethals naturally in this short interval is highly improbable, the effect of ultra-violet light was definitely established. When I began working on this problem in 1932, no results had been published concerning the effects of alpha-radiation on Drosophila. Since then, Hanson published, in December of 1933, a note reporting that he had produced somatic variations and mosaics by means of alpha-radiation. I thought it would be of interest to investigate the genetic effects of alpha-radiation, and particularly whether germinal mutations could be produced. An important property of alpha-radiation, which is not common to any of the other types of radiation tested above, is that the ionization is not uniform but is concentrated along the extremely narrow paths of the alpha-particles; and along these paths the ionization is extremely intense. On this account it seemed that some interesting results might be obtained with alpha-rays which do not occur with the other types of radiation.

The problem of the energy relationship is fundamental in any investigation of animal physiology. Endoparasitic helminths present a rather unique ecological situation since the energy sources and substrates for the parasite are dependent more upon the vagaries of the individual species and even strain of host animal in which they are found than on the individual efforts of the parasite. Fat metabolism is a good criterion for the evaluation of several aspects of the relationships between the host and the parasite. It is sensitive to both anaerobic and aerobic metabolic activities and because of its stability it is also effective in analyzing the response of the parasite to various environmental changes. Some aspects of the metabolism of the fat component of the rat cestode, Hymenolepis diminuta, are presented here. Considering the chemical pathways involved in the deposition of fatty materials it is soon realized that investigations on intermediary lipid metabolism are made quite complex by the fact that in the study of the chemical reactions involving fats, it is necessary to adequately consider those involving carbohydrates. A detailed elucidation of the basic metabolic pathways in the parasite is an essential basis for the clear understanding of the energy relationships between parasite and host. For this reason, an extensive review of the literature with particular attention to the development of the current concept of fat metabolism is presented. This, it is hoped, will clarify not only the mechanisms involved in the immediate area of intermediary metabolism, but also it will illustrate the importance of other metabolic areas as seen through the activity of the basic two-carbon unit.

The static aspects of the diaphragm under Full Residual Capacity (full lung deflation) were studied. The membrane equations were used to describe the diaphragm. Based on the description, a finite element program was written to determine the position of the diaphragm under various loading conditions. Erect and supine specimens were studied. The results of the finite element model were found to be in agreement with physiological data from X-ray photographs.

O$\sb2$ transport was examined by measuring the fractional saturation of concentrated hemoglobin solutions flowing through an artificial capillary (diameter $\approx$ 27 $\mu$m). The measured effects of pH, hemoglobin concentration, O$\sb2$ tension, temperature, and organic phosphate were analyzed by a mathematical model which included the geometry of the capillary, parabolic flow inside the lumen, and cooperative O$\sb2$ binding. Oxygen exchange was limited by diffusion and therefore governed by the magnitude of the O$\sb2$ gradient between the intracapillary fluid phase and the external gas space. In uptake experiments, O$\sb2$ flux was determined primarily by the external O$\sb2$ tension (160 mm Hg) because the internal O$\sb2$ pressure was kept small due to chemical combination with hemoglobin. In release experiments, the external O$\sb2$ tension was maintained at zero, and the transport rate was determined by the intracapillary oxygen partial pressure, which was proportional to the O$\sb2$ half-saturation pressure of the hemoglobin sample. Thus, factors that change the affinity of hemoglobin for oxygen, such as pH, temperature, and organic phosphate concentration, influence strongly the rate of O$\sb2$ release but have little effect on the rate of O$\sb2$ uptake. The rate-limiting step for erythrocyte CO$\sb2$ transport is the transmembrane exchange of Cl$\sp-$ and HCO$\sb3\sp-$ anions. This process was measured by following extracellular pH changes using a pH-sensitive fluorescent dye in a stopped-flow mixing device equipped with front-face optics. Initial pH and chloride gradients induced pH relaxations which were sensitive to the specific inhibitor 4,4$\prime$-diisothiocyano-2,2$\prime$-stilbenedisulfonic acid (DIDS). Special mixing experiments, designed to minimize anion competition for the transporter binding site(s), were simulated mathematically by models written for ping-pong and random ternary complex mechanisms. The experimentally observed rate dependence on initial extracellular bicarbonate concentration was approximated better by the ping-pong model, and the theoretically derived values for Cl$\sp-$ and HCO$\sb3\sp-$ binding (both K$\sb {\rm D}$'s = 5 mM) as well as the translocation rate (1.1 $\times$ 10$\sp4$ s$\sp{-1}$) agreed very well with literature values for inhibition constants and protein turnover number, respectively. Finally the simultaneous measurement of O$\sb2$ uptake and subsequent HCO$\sb3\sp-$/Cl$\sp-$ exchange was demonstrated. The hemoglobin color change upon oxygen binding caused a rapid change in fluorescence, followed by a slower, DIDS-sensitive pH equilibration.

Consumption of the intercellular messenger, nitric oxide (NO), by extracellular hemoglobin causes the hypertensive side effect associated with current blood substitute products. Substitution of large aromatic amino acid side chains into the distal cavity of hemoglobin can decrease the rate of this NO scavenging reaction, and mitigate the hypertensive effect. However, such substitutions can also affect O2 binding and release by hemoglobin. To better define the impact of distal pocket mutation on O2 transport, several myoglobin prototypes were tested in an artificial capillary. In addition, a series of recombinant hemoglobins containing phenylalanine and tryptophan substitutions at key locations were characterized to examine how these mutations affect O2 and CO binding. Experiments measuring O2 release and uptake by mutant myoglobins in an artificial capillary demonstrate that delivery is dependent on the affinity of the protein, but that uptake is similar for all of the mutants. This shows that decreases in association rate constants are better tolerated than decreases in dissociation rate constants, and validates the connection between the equilibrium constant for O2 binding, and the physiological transport function of hemoglobin. Placement of Phe and Trp at positions B10, E11 and G8 within the distal pocket decreases the rate at which ligands can gain entry to the active site, which was expected based on similar behavior in myoglobin mutants. The B10 mutants have direct steric and electrostatic interactions with the ligand, seen in the 2000-fold decrease in rate of O2 association for the beta(Trp(B10)) and 60-fold decrease in the O2 dissociation rate constant for alpha(Phe(B10)) subunits. Substitution at position E11 increases O2 and CO affinity due to removal of the naturally occurring gamma2CH3 group of Val(E 11). The E11 mutants have less dramatic effects in hemoglobin than in myoglobin due to the absence of 'extra' volume in the back of the distal cavity in either hemoglobin subunit. Steric crowding by position G8 mutants decreases the rate and extent of ligand capture, particularly in beta subunits. In general, ideas developed for ligand binding in myoglobin translate well to hemoglobin, but structural details of each subunit can magnify or diminish the effect of the mutation.

Previous results indicate that the functional properties of myelinated axons are considerably more complex than previously believed. The purpose of this study was to further examine the functional properties of potassium conductances in dorsal and ventral root (DRA; VRA) frog myelinated axons by intracellular microelectrode recording. The voltage responses to hyperpolarizing current injection demonstrated: (1) a nonlinear voltage current (V/I) relationship in the region just below resting membrane potential; (2) a linear peak and steady state V/I relationship below $ approx$ $-$95 mV; (3) a large effective capacitance of the internodal membrane; and (4) an attenuation of the voltage response reflecting the activation of a voltage dependent anomalous rectifying conductance (G$ sb{ rm AR}$). G$ sb{ rm AR}$ is dependent on the presence of sodium and potassium ions in the external medium and is blocked by cesium but not barium ions. (5) An afterhyperpolarizing potential (AHP) after a train of action potentials was accounted for by the presence of a sodium dependent potassium conductance (G$ sb{ rm K(Na)}$). The functional role of the voltage dependent potassium conductances and G$ sb{ rm K(Na)}$ was examined. G$ sb{ rm AR}$ appears to regulate the length of a post tetanic AHP. Early accommodation (EAcc) is regulated by G$ sb{ rm Kf1}$ in DRA and VRA. Late accommodation (LAcc) and adaptation (Adp) is regulated by G$ sb{ rm Ks}$ in both DRA and VRA. G$ sb{ rm Kf2}$ may also contribute to EAcc and Adp. Action potential repolarization in DRA and VRA is governed by G$ sb{ rm Kf2}$ and G$ sb{ rm Kf1}$ respectively. G$ sb{ rm K(Na)}$ may also contribute to LAcc and Adp. An evaluation of our experimental results using a computer model based Hodgkin-Huxley type equations suggests that the gating of the sodium conductance plays only a minor role in accommodation and adaptation. These results indicate that potassium conductances play a pivotal role in regulating the excitabilit

The present study was undertaken primarily to determine the prevalence of ABCA1 gene defects in a selected population with a HDL-C < 5 th percentile. The results showed that 30% of the selected patients had a lipid efflux defect and 16% (10/64) of those patients had a mutation in the ABCA1 gene. The cholesterol and phospholipid efflux showed a high correlation with HDL-C levels. In addition, both phospholipid and cholesterol effluxes (r = 0.64 p < 0.001 and r = 0.48 p < 0.001, respectively) were significantly correlated to HDL-C levels in selected hypoalphalipoproteinemia subjects. / Knowing that ABCA1 is regulated by cholesterol, oxysterols, and cAMP in peripheral cells, it was also of interest to investigate the regulation in other cells where cholesterol metabolism is an important function. Therefore the second objective was to determine the regulation of ABCA1 in hepatocytes. The results demonstrated that ABCA1 was not regulated in HepG2 cells but strongly regulated in fibroblasts. / Taken together, these studies support the two-step hypothesis proposed by Fielding et al. These studies also suggest that ABCA1 regulation in the liver is different than in peripheral cells. We believe that understanding the ABCA1 pathway will lead to a better comprehension of the reverse cholesterol transport system.