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Biomedical subjects

K J Gibson

Publications and source records attributed to K J Gibson.

54 records · Page 3Linked to original sources
PubMed1993

The roles of arginine vasopressin in fetal sodium balance and as a mediator of the effects of fetal "stress".

To see if arginine vasopressin (AVP) influenced fetal sodium balance, we infused AVP i.v. (45 mU h-1 kg-1) into two groups of chronically catheterized fetal sheep. One group had urinary osmolalities of 147 +/- 23 mosm kg-1 (SEM, n = 6) and the other group had higher urinary osmolalities (339 +/- 3 mosm kg-1, n = 4, P < 0.001). The group with high urinary osmolalities had higher systolic pressures (P < 0.05), higher glomerular filtration rates (GFR; P < 0.05), and higher urinary electrolyte excretion rates (P < 0.05), but lower membrane blood flows (P < 0.05) and lower fractional reabsorption of sodium by the proximal tubule (P < 0.01). In the group with low urinary osmolalities, AVP caused a rise in arterial blood pressure (P < 0.001), a fall in heart rate (P < 0.001), a fall in membrane blood flow (P < 0.02), but no change in placental or renal blood flow. Renal sodium excretion increased (P < 0.001) because GFR rose (P < 0.001) and proximal fractional sodium reabsorption fell (P < 0.001). Distal fractional sodium reabsorption increased (P < 0.001), but not enough to compensate for the fall in proximal fractional reabsorption. Lung liquid flow decreased (P = 0.006), as did lung liquid sodium excretion (P = 0.002). There were no changes in fetal plasma sodium, blood volume or haematocrit. The effects of AVP infusion were similar in the group with high urinary osmolalities. This study shows that high levels of AVP, such as occur in fetal "stress", have widespread effects on fetal cardiovascular, renal and lung functions. The characteristic profile of the fetuses with high urinary osmolalities prior to AVP infusion could be entirely explained by high endogenous AVP levels and AVP could possibly be a sole mediator of these widespread effects of fetal "stress". Furthermore, although during infusion of AVP sodium excretion increased, blood volumes did not change. Therefore, the fetuses must have accessed additional sodium from either their extracellular fluids, the amniotic and/or allantoic cavities or across the placenta.

Animals↗
PubMed1992

Mechanisms by which the pregnant ewe can sustain increased salt and water supply to the fetus.

1. Nine chronically catheterized pregnant ewes were monitored before, during and after 1 week in which fetal urine was drained continuously, to determine whether they could compensate for the resulting loss of salt and water and increase net supply across the placenta to the fetus. 2. Fetal growth and urine and lung liquid production were not affected by loss of all fetal fluids. 3. When fetal urine was drained, the increase (P less than 0.05) in maternal drinking was greater than the extra amount of fluid lost. Thus, maternal plasma osmolality fell (P less than 0.01). When fetal urine again flowed into the amniotic and allantoic cavities, maternal drinking did not fall significantly and plasma osmolality remained low. Maternal urine flow rate increased (P less than 0.05) and its osmolality fell (P less than 0.02). 4. Maternal food intake increased (P less than 0.005) during fetal urine drainage. 5. Maternal plasma renin activity increased (P less than 0.05), her urinary sodium excretion fell (P less than 0.005) and the Na(+)-K+ ratio in both her urine and faeces decreased (P less than 0.01 and P less than 0.05 respectively) when fetal urine was drained. Maternal urinary and faecal sodium conservation continued after drainage ceased because of continued loss of sodium in lung liquid. 6. It is concluded that the ewe can compensate for inappropriate loss of salt and water from the conceptus.

Animals↗
PubMed1992

Potential early intermediates in anaerobic benzoate degradation by Rhodopseudomonas palustris.

Alkali-treated extracts of Rhodopseudomonas palustris growing photosynthetically on benzoate were examined by gas chromatography/mass spectrometry for partially reduced benzoate derivatives. Two cyclic dienes, cyclohexa-2,5-diene-1-carboxylate and cyclohexa-1,4-diene-1-carboxylate, were detected. Either compound supported cell growth as effectively as benzoate. These results suggest that these cyclohexadienecarboxylates, probably as their coenzyme A esters, are the initial reduction products formed during anaerobic benzoate metabolism by R. palustris.

Anaerobiosis↗
PubMed1991

Ferredoxins from two sulfonylurea herbicide monooxygenase systems in Streptomyces griseolus.

We have purified and characterized two ferredoxins, designated Fd-1 and Fd-2, from the soluble protein fraction of sulfonylurea herbicide induced Streptomyces griseolus. These cells have previously been shown to contain two inducible cytochromes P-450, P-450SU1 (CYP105A1) and P-450SU2 (CYP105B1), responsible for herbicide metabolism [O'Keefe, D. P., Romesser, J. A., & Leto, K. J. (1988) Arch. Microbiol. 149, 406-412]. Although Fd-2 is more effective, either ferredoxin can restore sulfonylurea monooxygenase activity to an aerobic mixture of NADPH, spinach ferredoxin:NADP oxidoreductase, purified cytochrome P-450SU1, and herbicide substrate. The gene for Fd-1 is located in the genome just downstream of the gene for cytochrome P-450SU1; the gene for Fd-2 follows the gene for P-450SU2. The deduced amino acid sequences of the two ferredoxins show that, if monomeric, each has a molecular mass of approximately 7 kDa, and alignment of the two sequences demonstrates that they are approximately 52% positionally identical. The spectroscopic properties and iron and acid-labile sulfide contents of both ferredoxins suggest that, as isolated, each contains a single [3Fe-4S] cluster. The presence of only three cysteines in Fd-1 and comparisons with three [4Fe-4S] ferredoxins with high sequence similarity suggest that both Fd-1 and Fd-2 have an alanine in the position where these [4Fe-4S] proteins have a fourth cysteine ligand to the cluster. Transformation of Streptomyces lividans, a strain unable to metabolize sulfonylureas, with DNA encoding both P-450SU1 and Fd-1 results in cells capable of herbicide metabolism. S. lividans transformants encoding only cytochrome P-450SU1 do not metabolize herbicide.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Changes in fetal and maternal plasma protein concentration and colloid osmotic pressure with gestation.

In pregnant ewes, plasma protein levels over the gestation age range of 58-141 days fell progressively (r = -0.332, P less than 0.05, n = 36) but colloid osmotic pressure (COP, mmHg) did not change significantly. In fetal sheep carried by these ewes, plasma protein levels increased with age (r = 0.85, P less than 0.00001, n = 32). COP also rose (r = 0.8, P less than 0.00001, n = 23). Since maternal COP did not change and fetal COP increased, the net transplacental COP gradient between mother and fetus decreased with increasing age (r = -0.589, P less than 0.004, n = 22). Fetal plasma protein levels can be used to calculate fetal COP while maternal plasma protein levels cannot be used to calculate maternal COP.

Animals↗
PubMed1989

DNA substrate structural requirements for the exonuclease and polymerase activities of procaryotic and phage DNA polymerases.

A DNA duplex covalently cross-linked between specific bases has been prepared. This and similar duplexes are substrates for the polymerase and exonuclease activities of the Klenow fragment of Escherichia coli DNA polymerase I and T4 and T7 DNA polymerases. The action of Klenow fragment on these duplexes indicates that the polymerase site does not require that the DNA duplex undergo strand separation for activity, whereas the exonuclease site requires that at least four base pairs of the primer strand must melt out for the exonucleolytic removal of nucleotides from the primer terminus. The exonucleolytic action of T4 and T7 DNA polymerases requires that only two and three bases respectively melt out for excision of nucleotides from the primer terminus. Klenow fragment and T4 DNA polymerase are able to polymerize onto duplexes incapable of strand separation, whereas T7 DNA polymerase seems to require that the primer terminus be at least three bases from the cross-linked base pair. A DNA duplex with a biotin covalently linked to a specific base has been prepared. In the presence of the biotin binding protein avidin, the exonucleolytic activity of Klenow fragment requires that the primer terminus be at least 15 base pairs downstream from the base with the biotin-avidin complex. On the other hand, the polymerase activity of Klenow fragment required that the primer terminus be at least six base pairs downstream from the base with the biotin-avidin complex. These results suggest that the polymerase and exonuclease sites of Klenow are physically separate in solution and exhibit different substrate structural requirements for activity.

Avidin↗
PubMed1989

Sensation seeking and marital adjustment.

Seventy-two married couples completed Zuckerman's Sensation Seeking Scale, Form V, and the Kimmel and VanderVeen modification of the Locke Marital Adjustment Questionnaire. Marital adjustment was not related to the difference between husbands' and wives' sensation-seeking scores, but a negative relationship was found between sensation seeking and marital adjustment for women but not for men. This suggests that high sensation seeking in women has a negative impact on their marital satisfaction independent of their husband's sensation-seeking score. Assortative mating for sensation seeking was also observed.

Adaptation, Psychological↗
PubMed1987

Synthesis and application of derivatizable oligonucleotides.

To investigate protein-DNA interactions, we have synthesized a versatile phthalimide-protected 5-(3-aminopropyl)-2'-deoxyuridine nucleoside probe. The modified residue was incorporated into deoxyoligonucleotides by automated synthesis. The standard oligonucleotide workup also exposed the pendent amino group, which was found to react with either fluorescent labelling agents or, as detailed below, a photoactivatable cross-linking agent. In the dark, a strand with a photolabile group adjacent to the 3' end served as a primer for synthetic template-directed DNA synthesis by the Klenow fragment of E. coli DNA polymerase I, by bacteriophage T4 DNA polymerase, and by avian myeloblastosis virus (AMV) reverse transcriptase. Brief illumination with 302 nm light afforded covalent complexes between DNA and the polymerases; labelling of AMV reverse transcriptase was predominantly in the beta subunit.

Bacterial Proteins↗
PubMed1984

Synthesis and biochemical evaluation of 2'-deoxy-lin-benzoadenosine phosphates.

2'-Deoxy-lin-benzoadenosine has been synthesized via reductive deoxygenation of 2-(beta-D-ribofuranosyl)-8-(methylthio)imidazo[4,5-g]quinazoline. The 5'-mono-, 5'-di-, and 5'-triphosphates have been prepared by chemical and/or enzymatic methods. The 5'-diphosphate was found to be a substrate for phosphorylation by pyruvate kinase and was compared with various natural and extended substrates in kinetic assays. When 2'-deoxy-lin-benzoadenosine 5'-triphosphate was tested in a nick-translation experiment with Escherichia coli DNA polymerase I, a very low level of 32P incorporation from [alpha-32P]TTP into poly[d(AT)] was observed. Nearest-neighbor analysis indicated that the analogue was not significantly incorporated into internal positions in the polymer. In DNA-sequencing reactions, the analogue caused chain termination at adensine residues, although termination was less uniform and less efficient than that with 2',3'-dideoxy-ATP. These experiments show that lin-benzoadenine can form a widened Watson-Crick base pair with thymine. They strongly suggest, though they do not prove, that the enzyme is able to attach the analogue to DNA.

Adenine Nucleotides↗
PubMed1984

Nucleoside 5'-(beta, gamma-peroxytriphosphates).

Procedures for the synthesis, purification, and characterization of beta, gamma-peroxy analogues of the eight common ribo- and deoxyribonucleoside triphosphates have been developed. Although adenosine 5'-(beta, gamma-peroxytriphosphate) was stable to conditions in most biochemical systems, incubation of a solution of the analogue at 100 degrees C led to formation of AMP and ATP, as well as ADP. NAD+ pyrophosphorylase was the only enzyme among 13 tested for which adenosine 5'-(beta, gamma-peroxytriphosphate) was a good substrate, but the analogue was an effective inhibitor for a number of kinases. The peroxy compounds tested inactive with Escherichia coli RNA polymerase and DNA polymerase I, as well as with wheat germ RNA polymerase II.

Adenosine Triphosphate↗
PubMed1982

Binding of the substrates and the allosteric inhibitor adenosine 5'-diphosphate to phosphoribosylpyrophosphate synthetase from Salmonella typhimurium.

The binding of the substrates, ATP and ribose-5-P, and the most effective inhibitor, ADP, to phosphoribosylpyrophosphate synthetase from Salmonella typhimurium was characterized using equilibrium dialysis of these compounds labeled with 32P. In the absence of ribose-5-P, ATP, ADP, and the ATP analogue alpha,beta-methylene ATP each bind cooperatively with half-saturation at 50 to 90 microM and Hill coefficients of 1.5 to 2. We propose that all three compounds bind at the same set of sites, which are presumably the active sites. When ribose-5-P was added, methylene ATP and ADP binding at these sites became tighter (Kd approximately 3 to 6 microM at 10 mM ribose-5-P) and lost its cooperativity. In the presence of ribose-5-P, ADP, but not methylene ATP, bound to a second site with half-saturation at approximately 150 microM and a Hill coefficient greater than 3. This result confirms the existence of an allosteric ADP site, which was previously postulated from kinetic studies (Switzer, R. L., and Sogin, D. C. (1973) J. Biol. Chem. 248, 1063-1073). Binding of ribose-5-P could not be detected in the absence of nucleotides, but it was readily measured in their presence. The apparent Kd of ribose-5-P varied from greater than 1 mM to approximately 5 microM as the concentration of either ADP or methylene ATP was increased from 0 to 2 mM. Inhibition of the enzyme by action of ADP at both active and allosteric sites could be observed kinetically.

Adenosine Diphosphate↗
PubMed1980

Structure of the divalent cation.nucleotide complex at the active site of phosphoribosylpyrophosphate synthetase.

When Mg2+ was used as the activating cation, the phosphoribosylpyrophosphate synthetase (EC 2.7.6.1) of Salmonella typhimurium showed absolute specificity for the A(S) enantiomer of adenosine 5'-O-(1-thiotriphosphate), which gave a Km of 72 +/- 10 microM and a Vmax of 111 +/- 5 mumol/min/mg. The corresponding values for ATP were 46 +/- 3 microM and approximately 107 mumol/min/mg. Under the same conditions the B(R) isomer was a linearly competitive inhibitor (Ki = 54 +/- 11 microM) with respect to ATP. When Cd2+ replaced Mg2+, the two isomers reacted at comparable rates (Vmax (A)/Vmax (B) approximately equal to 0.8). This change in specificity suggests that the alpha-phosphate of ATP is liganded to a divalent cation during catalysis. Adenosine 5'-O-thiomonophosphate was 34-fold more effective as a product inhibitor when Cd2+ replaced Mg2+, while the effectiveness of AMP was not altered. This result suggests a divalent cation bridge between the enzyme and the alpha-phosphate of nucleotides. The results of these and previously published experiments enable us to propose a structure and stereochemical configuration for the divalent cation.ATP complex at the active site of phosphoribosylpyrophosphate synthetase.

Adenosine Triphosphate↗
PubMed1977

Chemotaxis toward amino acids by Bacillus subtilis.

Conditions for assaying chemotaxis in Bacillus subtilis are described. The chemotaxis medium we used afforded excellent motility for hours. In it, chemotaxis measured by capillary assays was insensitive to pH between 5.5 and 9, and to temperature between 28 degrees C and 42 degrees C. Chemotaxis was observed toward all 20 common amino acids, with thresholds varying from 3nM for alanine to 0.1 mM for glutamate, in the capillary assay, and from 0.1 muM for alanine to 0.32 mM for glutamate in the microscope assay.

Amino Acids↗
PubMed1977

Amino acid chemoreceptors of Bacillus subtilis.

Specificities of chemoreceptors for the 20 common amino acids, toward which Bacillus subtilis shows chemotaxis, were assessed by competition ("jamming") experiments using a modification of the traditional capillary assay, called the "sensitivity capillary assay." Many amino acids were sensed by at least two chemoreceptors. All the highest affinity chemoreceptors for the amino acids were distinct, except glutamate and aspartate, which may share one chemoreceptor, and tyrosine, for which the data could not be collected due to low solubility. The data suggest the hypothesis that each amino acid-chemoreceptor complex binds to a different signaler (from each amino acid-chemoreceptor complex binds to a different signaler (from which signals travel to the flagella to modify behavior appropriately), and that many of the signalers can also bind other attractant-chemoreceptor complexes as antagonists (no signals to flagella).

Amino Acids↗
PubMedDate not supplied

Renal acid-base and sodium handling in hypoxia and subsequent mild metabolic acidosis in foetal sheep.

1. To measure the renal contribution to acid-base homeostasis during hypoxia (not associated with hypercapnia) and in response to the subsequent mild metabolic acidosis and to determine the effects of this hypoxia on the renal handling of sodium, studies were performed in six chronically catheterized foetal sheep (129-138 days gestation) before, during and for 1 h after a 2 h period of hypoxia. 2. Hypoxia was induced in the conscious ewe by infusing nitrogen into the trachea. Foetal arterial oxygen tension fell to 12.0 +/- 0.6 mmHg (P < 0.001). Carbon dioxide tension fell during hypoxia (P < 0.001) and was still somewhat reduced in the recovery period (P < 0.005). Arterial pH fell progressively to 7.19 +/- 0.08 in the recovery period (P < 0.05). Plasma bicarbonate concentrations fell (P < 0.001) and lactate rose (P < 0.001). 3. Urinary pH and the excretion rates of bicarbonate, titratable acid, ammonium and net acid did not change during hypoxia. Ammonium excretion and, hence, generation of new bicarbonate increased in the recovery period (P < 0.05). 4. Renal sodium excretion progressively increased and was greatest after normoxia was restored (P < 0.05). This natriuresis was due to a fall in the reabsorption of sodium by the proximal tubule (P < 0.05). Proximal reabsorption of sodium was directly related to foetal pH (P < 0.0001) and bicarbonate reabsorption (P < 0.001). 5. It was concluded that: (i) the foetal kidneys began to contribute to the maintenance of acid-base balance within the first hour of recovery from a 2 h episode of hypocapnic hypoxia, even though the acidosis was relatively mild; and (ii) a reduction in bicarbonate reabsorption was probably the most important factor that limited sodium reabsorption by the renal tubule during this experiment.

Acid-Base Equilibrium↗
PubMedDate not supplied

Effects on hypoxaemia on foetal heart rate, variability and cardiac rhythm.

1. Experiments were carried out in 30 chronically catheterized foetal sheep (128-144 days; term 150 days) and in seven of these foetuses before, during and after acute hypoxaemia. The extent to which changes in sympathoadrenal activity and cardiac vagal activity affected the foetal cardiac response to hypoxaemia was measured. Three measurements were used: foetal heart rate (FHR), heart rate variability (HRV; measured as the coefficient of variation in pulse interval) and power spectral density (PSD; measured over the frequency ranges of 0.04-1.3 Hz). Cardiac vagal activity was blocked by atropine, beta-adrenoceptor activity was blocked by propranolol. 2. Under normoxaemic conditions, cardiac vagal blockade caused a rise in mean arterial pressure (MAP; P < 0.001), an increase in FHR (P < 0.001), a decrease in HRV (P < 0.001) and a decrease in PSD (P < 0.001). beta-adrenoceptor blockade caused a rise in MAP (P < 0.001), a fall in FHR (P < 0.01), a decrease in HRV (P < 0.001) but no change in PSD. 3. During mild hypoxaemia (PO2 = 12-14.5 mmHg) and moderate hypoxaemia (PO2 = 10-11.9 mmHg), foetal MAP (P < 0.001, P< 0.001), HRV (P < 0.01, P < 0.001) and PSD in the frequency range 0.04-0.45 Hz increased (P < 0.05-P < 0.001). Foetal heart rate decreased when foetuses became moderately hypoxaemic (P < 0.001). 4. After cardiac vagal blockade, hypoxaemia was associated with an increase in FHR compared with non-blocked hypoxaemic foetuses (P < 0.01, P < 0.001). The increase in HRV was abolished (P < 0.001, P < 0.001) as was the increase in PSD (P < 0.01-P < 0.001). 5. After beta-adrenoceptor blockade, the bradycardia that occurred during hypoxaemia was enhanced (P < 0.01, P < 0.05), the increase in HRV was not affected and neither was the increase in PSD. 6. As FHR and HRV of normoxaemic foetal sheep were affected both by atropine and propranolol, it would seem that both cardiac vagal and sympathoadrenal activity modulate the foetal heart under resting conditions. The lack of any effect of beta-adrenoceptor blockade on PSD under these conditions suggests that power spectral analysis (PSA) is not as sensitive as the other two methods in detecting sympathetically mediated modulation of the heart. 7. Because the hypoxaemia induced bradycardia and increase in HRV and in PSD were abolished by atropine (P < 0.01-P < 0.001), it is concluded that during hypoxaemia foetal HRV is mainly modulated by changes in cardiac vagal tone. Propranolol had no effect on foetal HRV, although it reduced it under normoxaemic conditions; therefore, it is concluded that cardiac sympathetic neural activity was not increased in acute hypoxaemia uncomplicated by acidosis. However, there was strong evidence of increased sympathoadrenal tone on the foetal heart in hypoxaemia, that is, there was a rise in FHR in hypoxaemic atropinized foetuses and a greater fall in FHR in beta-adrenoceptor blocked hypoxaemic foetuses. Therefore, this increased sympathetic influence on the foetal heart during hypoxaemia must be predominantly the result of increased adrenomedullary secretion of catecholamines. 8. Maintenance of foetal cardiac output depends on the chronotropic and ionotropic effects of catecholamines. Therefore, this adrenomedullary influence on the foetal heart during hypoxaemia is important to offset the opposing effects of increased cardiac vagal tone.

Adrenergic beta-Antagonists↗