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Biomedical subjects

J A Fox

Publications and source records attributed to J A Fox.

At least 73 records · Page 4Linked to original sources
PubMed1983

Thallous ion permeation through the cation-selective channel of the sarcoplasmic reticulum. Anomalous mole fraction dependence.

The thallous ion was found to permeate the cation-selective channel of rabbit sarcoplasmic reticulum and to block current through this channel when present in mixtures with other permeant ions. Channel conductance in pure thallium acetate saturates with increasing concentration, with a maximum limiting conductance of 60 pS. The conductance ratio GK/GTl at 1 M is 3.7, while the permeability ratio is near 0.4 over the concentration range 0.01 to 1 M. Thallium blockade in mixtures can be described by the equation of Neher (Neher, E. (1975) Biochim. Biophys. Acta 401, 540-544).

Animals↗
PubMed1983

Paramagnetic centers in the nickel-containing, deazaflavin-reducing hydrogenase from Methanobacterium thermoautotrophicum.

Two hydrogenases from the methanogenic bacterium Methanobacterium thermoautotrophicum strain DeltaH have been purified and contain tightly bound nickel as well as the anticipated iron/sulfur atoms with a fixed ratio of 15-20 iron atoms per nickel. One hydrogenase reduces the 8-hydroxy-5-deazaflavin coenzyme factor 420 (F(420)), whereas the other has been purified as a methyl viologen-reducing hydrogenase. Both enzymes possess an EPR signal attributed to paramagnetic nickel as demonstrated by hyperfine coupling in (61)Ni-containing hydrogenases. Comparison to model compounds suggests a nickel(III) oxidation state in the inactive forms of these aerobically purified enzymes. Loss of the nickel(III) signal accompanies reductive activation but is not kinetically correlated with regain of high specific activity. On replacement of H(2) by argon in the gas phase over reduced, active, F(420)-reducing enzyme, several EPR signals appear, including a signal at g = 2.004 that is probably enzyme-bound FADH semiquinone, two signals at g = 2.140 and 2.196 that reflect a new form of paramagnetic nickel(III), and also a signal at g = 2.036 that may be an iron signal. The F(420)-reducing hydrogenase in the second paramagnetic nickel form is either itself active or in facile equilibrium with active enzyme. The size of the signal at g = 2.036 may correlate with the degree of activation of the enzyme. In contrast to the hydrogenase of Clostridium pasteurianum [Erbes, D. L., Burris, R. H. & Orme-Johnson, W. H. (1975) Proc. Natl. Acad. Sci. USA 72, 4795-4799], which appears to use only iron/sulfur prosthetic groups and which reacts with one-electron-transfer agents, this methanogen hydrogenase seems to utilize iron, nickel, and flavin redox sites and to reduce obligate one-electron (viologen) and two-electron (deazaflavin) oxidants.

Coenzymes↗
PubMed1983

Absorption of Rickettsia rickettsii antibodies by Rickettsia rickettsii antigens in four diagnostic tests.

Immunoabsorption profiles were determined for Rickettsia rickettsii antigens used in four confirmatory tests for detection of antibodies to Rocky Mountain spotted fever. A human serum reactive in the four tests was absorbed with each test antigen and then reexamined by all four tests. The results indicated that the whole organism and complement-fixation antigen absorbed the whole array of antibodies to R. rickettsii, whereas erythrocyte-sensitizing substance coated on latex or erythrocytes did not. With erythrocyte-sensitizing substance coated on latex there was a decrease in titer when tested by the latex, indirect hemagglutination, and complement fixation tests but none when tested by the microimmunofluorescence test. With erythrocyte-sensitizing substance coated on sheep erythrocytes there was a decrease in titer when tested by indirect hemagglutination or complement fixation but none when tested by latex or microimmunofluorescence. These findings confirm that erythrocyte-sensitizing substance contains more than a single antigenic substance and plays a major role in the complement fixation test and a minor role in the microimmunofluorescence test.

Antibodies, Bacterial↗
PubMed1983

Uptake and release of calcium by canine gastric corpus smooth muscle plasma membrane enriched fraction.

Calcium movements across plasma membrane enriched vesicles isolated from canine gastric corpus smooth muscle were investigated. The ATP-dependent Ca2+ uptake increased with time up to 10 min. The uptake for the initial 2-min period was approximately linear with time. The apparent initial velocity of the ATP-dependent Ca2+ uptake increased monotonically with free Ca2+ concentration from 0.1 to 2 microM, and further increases in free Ca2+ concentration did not increase the Ca2+ uptake. The free Ca2+ dependence curve could be described with a Hill coefficient of approximately 1.0 and Km of 0.85 +/- 0.01 microM for free Ca2+ concentration. Passive Ca2+ uptake (reaction time = 1 h) also increased with increasing free Ca2+ concentrations from 0.02 to 4.0 mM. Dilution of loaded vesicles in isotonic media containing EGTA led to initial rapid loss (less than 1 min) followed by a slower release which showed simple exponential decay. The t 1/2 values of the slower Ca2+ loss from these vesicles were 16.1 +/- 0.9 min (actively loaded n = 5) and 18.4 +/- 0.9 min (passively loaded n = 3), respectively. Dilution in isotonic medium containing both EGTA and A23187 released all the sequestered Ca2+ from these loaded vesicles.

Adenosine Triphosphate↗
PubMed1982

Purification and properties of an 8-hydroxy-5-deazaflavin-reducing hydrogenase from Methanobacterium thermoautotrophicum.

A coenzyme F430-reducing hydrogenase from Methanobacterium thermoautotrophicum has been purified 25-fold, to approximately 50% homogeneity. Following anaerobic preincubation in high salt under reducing conditions, the purified enzyme exhibits equal catalytic activity (turnover number = 725 s-1) toward the artificial 1-electron acceptor, methyl viologen, and the physiological 2-electron acceptor, 7,8-didemethyl-8-hydroxy-5-deazaflavin (F420). The enzyme had the following Km values (micromolarity) under the described assay conditions: 420 (methyl viologen, pH 9.0), 19 (F420, pH 7.2), 34 (Fo, 7.8-didemethyl-8-hydroxy-5-deazariboflavin, pH 7.2), 10 (H2, Fo as co-substrate, pH 7.2), 2 (H2, methyl viologen as co-substrate, pH 9.0). The native protein is oligomeric (apparent Mr greater than 500,000) and is composed of three distinct subunits with Mr - 40,000, 31,000, and 26,000 in the ratio of 2:2:1, leading to a minimum Mr = 170,000. In addition to 33 atoms of Fe and 24 atoms of acid-labile sulfur, the F420-hydrogenase contains 2.3 mol of FAD/mol of Mr - 170,000. This activity is chromatographically distinct from a smaller methanogen hydrogenase capable of rapid viologen reduction, but which only very slowly reduces 5-deazariboflavins.

Euryarchaeota↗
PubMed1981

The development, factor analysis, and revision of a client satisfaction form.

Community Mental Health Centers often include the client in evaluation of services through the use of comprehensive and lengthy client satisfaction surveys. However, the results are often uniformly positive across the many issues on the survey, suggesting that many items are redundant. A comprehensive client satisfaction survey form containing 33 items was developed and administered to 170 terminated clients of three mental health agencies. A factor analysis of the data revealed dimensions of Satisfaction with Services, Acceptability of Clinician, Impact of Services, and Dignified Treatment. Demographic variables were not correlated with the factors. The original survey was reduced to 10 items and a Comments block. The 10 items are representative of the four factors and also included selected aspects of the agencies' programs and administration. The revised form can be used in a wide range of mental health settings.

Adolescent↗
PubMed1980

Deamination of 2-aminopropanol by ethanolamine ammonia-lyase, an AdoCbl-requiring enzyme. Kinetics and isotope effects for the R and S enantiomers of the substrate.

Both (R)-2-aminopropanol and (S)-2-aminopropanol are substrates for ethanolamine ammonia-lyase, reacting to yield propionaldehyde and ammonia via a common enzyme-bound intermediate. (S)-Propanolamine shows a lower Km and a higher Vmax than the R enantiomer, indicating that the former is a substantially better substrate than the latter. From the isotope effects and other considerations, it appears that the rate-limiting step for (S)-propanolamine is the same as that for ethanolamine, namely, the transfer of hydrogen from the cofactor to the product. In contrast, isotope effects seen with (R)-propanolamine indicate that there are two rate-limiting steps, both located in the segment of the reaction mechanism which is unique to the R enantiomer. One of these is the transfer of hydrogen from the substrate to the cofactor. The other is a subsequent step whose rate is similar to that of the first hydrogen transfer step but which does not involve the rupture of a carbon-hydrogen bond. It is speculated that this second rate-limiting step may have to do with the migration of the amino group.

Ammonia-Lyases↗
PubMed1980

The MacAndrew Scale as a measure of substance of abuse and delinquency among adolescents.

Used regression equations to determine the predictive power of the abbreviated MacAndrew Scale of the MMPI-168 on self-reported delinquent behavior of 1,672 suburban high school students. The abbreviated MacAndrew Scale score successfully predicted alcohol abuse, but was also shown to be related to crimes against property and persons and to marijuana usage. It was concluded that the MacAndrew Alcoholism Scale may not be uniquely sensitive to alcohol abuse among the population sampled.

Adolescent↗
PubMed1979

A horseradish peroxidase study of primary afferent projections to the medullary cuneate nucleus in the rat.

HRP was used to label first order afferent cells of the dorsal root ganglia which synapse at the cuneate nucleus. The results show that it is a population of predominantly large cells that project monosynaptically to the medullary cuneate nucleus and thus support anatomical and physiological studies showing that directly projecting axons to the dorsal column nuclei are larger, faster and conduct information from a select class of sensitive cutaneous mechanoreceptors. The finding, that approximately 20% of DRG neurons can be labeled from the dorsal column nuclei, is consistent with previous estimates of dorsal root fiber projections in the dorsal column based on Marchi degeneration.

Afferent Pathways↗
PubMed1979

Role of Ca2+ in genesis of lower esophageal sphincter tone and other active contractions.

The effects of absent or low Ca2+ (0.5 mM), verapamil, nifedipine, Na nitroprusside, theophylline, La2+, and ethanol on basal active tension (tone), "off" contractions, and carbachol contractions were studied in opossum lower esophageal sphincter strips. Incubation in Ca2+-free Ringer (0.1 mM EGTA) abolished tone and contractions. Low Ca2+, verapamil, nifedipine, and theophylline depressed tone more rapidly than "off" contractions. Only verapamil and nifedipine depressed carbachol contractions. Na nitroprusside rapidly depressed tone but left contractions unchanged. La3+ at 1 X 10(-3) M behaved like Ca2+-free incubation but produced sustained contractions with muscle stimulation. Ethanol depressed "off" contractions more than tone and did not affect carbachol-induced contractions. These results suggest that tone probably results from inward leak of Ca2+, whereas "off" contractions depend on release of Ca2+ sequestered in the cell by a mechanism not immediately dependent on increased Ca2+ influx. Carbachol may increase Ca2+ influx as well as utilize sequestered Ca2+. Nifedipine and verapamil may act to block both resting and stimulated Ca2+ influx. Na nitroprusside may act by increasing Ca2+ efflux. Ethanol may act by decreasing the availability of sequestered Ca2+ or by inhibiting the function of a mediator responsible for "off" contractions.

Animals↗