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Biomedical subjects

J Field

Publications and source records attributed to J Field.

At least 145 records · Page 8Linked to original sources
PubMed1987

Low-power NMR volume selection by slicing z magnetization.

A novel method for reducing the rf power requirements of selective pulses employed for z magnetization slice inversion in localized NMR spectroscopy is presented. Following slice preparation by the use of frequency-incremented sinc pulses, the slice gradient is reduced, which narrows the frequency width of the slice. This allows the use of relatively low-power selective inversion pulses, an important consideration for in vivo applications.

Bone Marrow↗
PubMed1987

Transaxillary angiography: an acceptable approach when perfemoral angiography is not acceptable.

Transaxillary angiography has been performed in a consecutive series wherever patients were unsuitable for perfemoral angiography. Between 1984 and 1986, transaxillary angiography was performed for 103 patients (81 males and 22 females with a mean age of 64 years). Major complications occurred in 2 patients (1.9%) who required surgical embolectomy with no long term sequelae. Three (2.9%) had a transient neurological deficit which lasted less than 1 week. In our hands transaxillary angiography is the best alternative when perfemoral angiography is not possible.

Adult↗
PubMed1987

Guanine nucleotide activation of, and competition between, RAS proteins from Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, yeast RAS proteins are potent activators of adenylate cyclase. In the present work we measured the activity of adenylate cyclase in membranes from Saccharomyces cerevisiae which overexpress this enzyme. The response of the enzyme to added RAS2 proteins bound with various guanine nucleotides and their analogs suggests that RAS2 proteins are active in their GTP-bound form and are virtually inactive in their GDP-bound form. Also, active RAS2 protein is not inhibited by inactive RAS2, suggesting that the inactive form does not compete with the active form in binding to its effector.

Adenylyl Cyclases↗
PubMed1986

RAM, a gene of yeast required for a functional modification of RAS proteins and for production of mating pheromone a-factor.

We have identified a gene (SUPH) of S. cerevisiae that is required for both RAS function and mating by cells of a mating type. supH is allelic to ste16, a gene required for the production of the mating pheromone a-factor. Both RAS and a-factor coding sequences terminate with the potential acyltransferase recognition sequence Cys-A-A-X, where A is an aliphatic amino acid. Mutations in SUPH-STE16 prevent the membrane localization and maturation of RAS protein, as well as the fatty acid acylation of it and other membrane proteins. We propose the designation RAM (RAS protein and a-factor maturation function) for SUPH and STE16. RAM may encode an enzyme responsible for the modification and membrane localization of proteins with this C-terminal sequence.

Acylation↗
PubMed1986

Magnetic resonance imaging--first human images in Australia.

The use of magnetic resonance imaging, in the demonstration of internal human anatomy and in the diagnosis of disease, has the major advantages that the technique is noninvasive, does not require the use of ionizing radiation and that it can demonstrate neurological and cardiovascular lesions that cannot be diagnosed easily by other imaging methods. Magnetic resonance imaging is derived from the principle that certain atomic nuclei in a strong magnetic field will absorb pulses of radiofrequency energy; when the pulse is finished the nuclei will emit radiowaves at the same frequency. These radiowaves are received by specially designed aerials or coils and the information is collected by a computer which reconstructs an image of internal anatomy in a similar way to that of x-ray computed tomography (CT). By changing the strength of the magnetic fields and the frequency of the radiowave pulses, it is possible to examine different sections within the body. The first magnetic resonance images of humans were obtained in Australia in October 1985 on the research instrument of the Queensland Medical Magnetic Resonance Research Centre, which is based at the Mater Hospital in Brisbane, and is part of the University of Queensland's Department of Radiology.

Abdomen↗
PubMed1986

The adenovirus DNA binding protein and adenovirus DNA polymerase interact to catalyze elongation of primed DNA templates.

The adenovirus-encoded 140-kDa DNA polymerase (Ad Pol) and the 59-kDa DNA binding protein (Ad DBP) are both required for the replication of viral DNA in vivo and in vitro. Previous studies demonstrated that, when poly(dT).oligo(dA) was used as a template-primer, both proteins were required for poly(dA) synthesis. In this report, the interaction between the Ad Pol and Ad DBP was further investigated using poly(dT).oligo(dA) as well as a linear duplex molecule containing 3' poly(dT) tails. DNA synthesis with the tailed template required Ad Pol, Ad DBP, and an oligo(dA) primer hydrogen bonded to the poly(dT) tails. Incorporation was stimulated 8-10-fold by ATP; however, no evidence of ATP hydrolysis to ADP was observed. Synthesis was initiated at either end of the tailed molecule and proceeded through the duplex region to the end of the molecule. This ability to translocate through duplex DNA and to synthesize long poly(dA) chains suggests that the Ad Pol.Ad DBP complex can act efficiently in the elongation reactions involved in the replication of Ad DNA (both type I and type II). During the replication reaction, substantial hydrolysis of deoxynucleoside triphosphates to the corresponding deoxynucleoside monophosphates occurred. This reaction required DNA synthesis and most likely reflects an idling reaction similar to that observed with other DNA polymerases containing 3'----5' exonuclease activity in which the polymerase first incorporates and then hydrolyzes a dNMP.

Adenosine Triphosphate↗
PubMed1986

Preliminary studies on the potential of in vivo deuterium NMR spectroscopy.

Natural abundance deuterium NMR spectroscopy can be used to characterise in vivo 2H signals arising from water and fat in mice, with acquisition times of less than two minutes. Administration of D(2)0 (10% V/V) in the drinking water enhances these signals so that excellent spectra can be obtained with one scan. Using these procedures the in vivo turnover of 2H in water and fat in mice has been determined. This procedure may be of particular importance in studies of fat turnover in obesity.

Adipose Tissue↗
PubMed1986

In vivo determination of 31P spin relaxation times (T1, T2, T1 rho) in rat leg muscle. Use of an off-axis solenoid coil.

A probe using a solenoid coil tilted 45 degrees off-axis has been used to study the 31P NMR relaxation characteristics of the resonances arising from phosphorus metabolites in rats in vivo. T1, T1 rho and T2 values have been determined for phosphocreatine and ATP in leg muscle. The ratio of 31P T1(1700ms) to T2(12ms) for ATP was in excess of 200:1 compared with a ratio of 5:1 for 1H T1:T2. Of major significance was the observation that T2 values for phosphocreatine (230ms) were markedly longer than T2 values for ATP (12ms). Thus by use of appropriate delay times in spin echo sequences ATP signals can be nulled, and discrete 31P imaging of phosphocreatine in muscle may be possible provided the overall signal-to-noise is satisfactory.

Animals↗
PubMed1986

Cloning and characterization of the high-affinity cAMP phosphodiesterase of Saccharomyces cerevisiae.

A gene, PDE2, has been cloned from the yeast Saccharomyces cerevisiae that, when present in high copy, reverses the phenotypic effects of RAS2Val19, a mutant form of the RAS2 gene that renders yeast cells sensitive to heat shock and starvation. It has previously been shown that the RAS proteins are potent activators of yeast adenylate cyclase. We report here that PDE2 encodes a high-affinity cAMP phosphodiesterase that shares sequence homology with animal cell phosphodiesterases. These results therefore imply that the effects of RAS2Val19 are mediated through its changes in cAMP concentration.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1986

Comparison of two methods of islet preparation and transplantation in dogs.

Seventy-nine mongrel dogs underwent total pancreatectomy. Fifteen dogs served as apancreatic controls and died 7.0 +/- 4.2 days later (mean +/- SD). The pancreases of 44 dogs (group 1) were intraductally distended by manual injection of Hanks' balanced salt solution (HBSS). Thereafter each organ was mechanically disrupted and subjected to collagenase digestion as described by Mirkovitch et al. The pancreases of 20 dogs (group 2) were intraductally distended and subsequently perfused with collagenase by a roller pump. The organs were then mechanically disrupted and filtered through screens as described by Horaguchi et al. The resulting tissue suspensions were injected into the spleens of the dogs as autotransplants in both groups, by direct punction of the splenic capsule in group 1 and by retrograde infusion via a splenic vein tributary in group 2. The functional outcome was better in group 2 than in group 1, as assessed by the number of animals that became normoglycemic after transplantation [15/20 (75%) vs. 13/44 (30%); P = .0025]. The degree of islet purification, as measured by an increase in the tissue insulin/amylase ratio, was higher in group 2, and in both groups it was higher in normoglycemic than in hyperglycemic animals. The percent engraftment [i.e., amount of insulin recovered from spleen as percent of tissue transplanted (mean, 15.4% in group 1 and 14.5% in group 2) or as percent of original pancreas (mean, 4.9% in group 1 and 4.4% in group 2)] was low in both groups but again was higher in normoglycemic than in hyperglycemic animals within each group. In conclusion, both the degree of engraftment and purification and the route of implantation influenced the functional outcome after dispersed pancreatic islet autotransplantation to the spleen of totally pancreatectomized dogs, with purified tissue injected retrogradely functioning better than unpurified tissue injected directly.

Amylases↗
PubMed1986

Exploring the function of RAS oncogenes by studying the yeast Saccharomyces cerevisiae.

The RAS oncogenes comprise a family of genes found to be activated in perhaps 10-20% of human cancers and which have been highly conserved in evolution. Homologs of the mammalian RAS exist in the yeast Saccharomyces cerevisiae (RAS1 and RAS2). We have shown that human ras proteins can complement the loss of RAS1 and RAS2 proteins in yeast, and hence are functionally homologous. Both human and yeast RAS proteins can stimulate the magnesium and guanine nucleotide-dependent adenylate cyclase activity present in yeast membranes. However, RAS proteins do not appear to stimulate adenylate cyclase in vertebrate cells. Our studies indicate that although RAS proteins are essential controlling elements of adenylate cyclase in yeast, they have other essential functions in that organisms. RAS proteins are themselves probably controlled by growth regulatory proteins.

Fungal Proteins↗
PubMed1985

In vitro metabolism of [2-13C]-ethanol by 1H NMR spectroscopy using 13C decoupling with the reverse dept polarization-transfer pulse sequence.

The metabolism of [2-13C]-ethanol by alcohol dehydrogenase purified from Drosophila melanogaster has been observed by proton nuclear magnetic resonance spectroscopy (NMR). The reverse-DEPT pulse sequence, with composite pulse 13C decoupling to simplify and increase the signal-to-noise of spectra, has been used to eliminate the strong water signal while still observing the proton signals of metabolites of interest. Using these techniques the rates of synthesis of acetaldehyde, its diol and acetate from [2-13C] ethanol by alcohol dehydrogenase were measured simultaneously.

Acetaldehyde↗
PubMed1985

Use of high-resolution 31P-labeled topical magnetic resonance spectroscopy to monitor in vivo tumor metabolism in rats.

A probe using a single-tuned solenoid coil has been constructed to study in vivo metabolism of rats in a wide-bore Bruker nuclear magnetic resonance spectrometer. Transplantable rat mammary adenocarcinomas (estrogen receptor negative) were implanted into the hind leg muscle of 8-week-old rats. The other leg without tumor was used as a control. Tumor metabolism could be distinguished from that of surrounding muscle by the appearance of inorganic phosphate and sugar phosphate resonances, reflecting tissue necrosis, and increased glycolysis. Tumor growth was accompanied by an increase in the size of these peaks, and the chemical shifts of the inorganic phosphate peak indicated that the intracellular pH became more acidic. Administration of methotrexate (i.v.) reversed these patterns and decreased tumor volume. Changes in the phosphocreatine peaks indicated changes in tumor volume rather than in tumor metabolism. These studies show that topical magnetic resonance not only can monitor the growth of tumors in vivo but can be also used to evaluate the efficacy of chemotherapeutic drugs.

Animals↗
PubMed1984

In vivo 13C nuclear magnetic resonance spectroscopy using a solenoid transmit/receiver coil.

Topical nuclear magnetic resonance spectroscopy (NMR) using a solenoid transmit/receiver coil has been used to monitor the kinetics of intragastric utilization of [1-13C] glucose in mice in vivo. Using a double-tuned solenoid coil, signal to noise response was excellent and the natural abundance in vivo 13C spectra obtained with acquisition times of 10-15 minutes compares more than favourably with comparable studies using surface or saddle coils. This study clearly shows the potential of solenoid coils to monitor the kinetics of 13C-labelled metabolites in vivo.

Animals↗
PubMed1984

Properties of the adenovirus DNA polymerase.

The 140,000-Da adenovirus-encoded DNA polymerase (Ad Pol) is required for viral DNA replication both in vitro and in vivo. The polymerase co-purifies in a complex with the 80,000-Da precursor (pTP) of the terminal protein (TP) found covalently attached to the 5' ends of adenovirus DNA. To better understand their function in DNA replication, we have examined the properties of the Ad Pol and the pTP X Ad Pol complex on natural and synthetic DNA templates. The pTP X Ad Pol complex utilizes a variety of homopolymer template-primer combinations including poly(dC) X oligo(dG), poly(dA) X oligo(dT), poly(dT) X oligo(dA), and poly(dT) X oligo(rA). With poly(dT) as template and oligo(rA) or oligo(dA) as primer, DNA synthesis by the pTP X Ad Pol complex is stimulated as much as 100-fold by the 59,000-Da adenovirus DNA-binding protein (Ad DBP). ATP (4 mM) can further increase the rate of DNA synthesis 3- to 10-fold. The Ad DBP does not stimulate the activity of host (HeLa cell) DNA polymerase alpha with poly(dT) X oligo(dA) (or oligo(rA)) as the template-primer, and Escherichia coli single-stranded DNA binding protein cannot substitute for the Ad DBP in the stimulation of the Ad Pol activity. Under optimal conditions, poly(dA) chains 30,000 nucleotides in length are formed indicating that the Ad Pol can be a highly processive enzyme. An exonuclease activity co-sediments with the pTP X Ad Pol complex during glycerol gradient centrifugation, and co-purifies with the 140,000-Da Ad Pol after dissociation of the pTP X Ad Pol complex with urea. The Ad Pol-associated nuclease hydrolyzes single-stranded DNA in a 3'----5' direction and is at least 10-fold more active on single-stranded DNA than on duplex DNA. The Ad Pol has no detectable endonuclease activity on single-stranded DNA or duplex circular DNA. Analysis of the products of the nuclease activity showed that 5'-deoxynucleoside monophosphates were released during the hydrolysis of single-stranded DNA. The Ad DBP inhibits the hydrolysis of DNA by the polymerase-associated nuclease activity.

Adenosine Triphosphate↗
PubMed1984

Purification of a primase activity associated with DNA polymerase alpha from HeLa cells.

Highly purified preparations of eukaryotic DNA polymerase alpha have been shown to contain primase activity (Kaguni, L.S., Rossignol, J-M., Conaway, R.C. Banks, G.R., and Lehman, I.R. (1983) J. Biol. Chem. 258, 9037-9039; Yagura, T., Kozu, T., and Seno, T. (1982) J. Biol. Chem. 257, 11121-11127; Shioda, M., Nelson, E.M., Bayne, M.L., and Benbow, R.M. (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 7209-7213). We have investigated the de novo synthesis of DNA by a primase-DNA polymerase alpha preparation isolated from human HeLa cells using the synthetic homopolymers poly(dT) and poly(dC) as templates. In the presence of poly(dT), synthesis of poly(dA) required ATP in addition to dATP while synthesis of poly(dG) in the presence of poly(dC) required GTP in addition to dGTP. The primase activity required a much lower GTP concentration (Km = 0.1 mM) than ATP (Km = 0.8 mM) for the synthesis of DNA. Guanosine 5'-O-(3-thiotriphosphate), 5'-guanylyl-beta, gamma-imidodiphosphate, and 5'-guanylyl methylenediphosphonate substituted for GTP but the corresponding ATP analogues did not substitute for ATP. Furthermore, ATP and ATP analogues inhibited the GTP-dependent reaction while GTP and GTP analogues inhibited the ATP-dependent reaction. DNase treatment of products labeled with [alpha-32P] GTP revealed that an RNA oligomer was covalently linked to newly synthesized DNA. Alkaline hydrolysis of these products yielded GMP and pppGp, indicating that the primer was initiated with GTP. Alkaline hydrolysis of [alpha-32P]dGTP-labeled products yielded 2'- and 3'-GMP showing that DNA chains are covalently linked to the 3' ends of RNA chains. The primase activity could not be separated from DNA polymerase alpha through a 200-fold enrichment involving phosphocellulose, DNA-cellulose, hydroxylapatite, DEAE-cellulose and glycerol gradient purification steps. However, primase activity was found to be less stable than DNA polymerase alpha activity under a variety of conditions.

Adenine Nucleotides↗