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Biomedical subjects

J Donlon

Publications and source records attributed to J Donlon.

14 recordsLinked to original sources
PubMed1991

Green light attenuates melatonin output and sleepiness during sleep deprivation.

Melatonin output covaries with sleepiness, with both peaking early morning. Bright white light suppresses this output, but it is not known if such treatment ameliorates nighttime sleepiness during sleep deprivation. However, sleep-deprived subjects find such light irritating. Humans are particularly sensitive to green light, and melatonin output is more readily suppressed by this hue. A pilot study using different green light regimens showed that sleep-deprived subjects well tolerated 2,000 lux green light given 10 min hourly, and that this dose reduced nighttime melatonin output. The main study gave this light treatment vs. a low intensity red/green light control, from 1900 hr for 11 hr, to two groups of subjects (n = 6 each) sleep deprived for 36 hr. Urine was collected at 6-hr intervals during sleep loss and on a baseline day. Vigilance performance, subjective sleepiness, and oral temperature were monitored during sleep loss. The experimental condition suppressed urine 6-hydroxymelatonin sulfate (aMT6s) output between 0000 hr and 0600 hr, and increased it 0600-1200 hr; but there was no change in total 24-hr values. The control condition had no such effects. The oral temperature rhythm remained unchanged. Vigilance and subjective sleepiness were improved significantly relative to control values during 0000-0600 hr; these improvements were maintained somewhat over the 0600-1200-hr period, contrary to what one might expect if the delayed melatonin surge at this time was increasing sleepiness. Although the bright green light helped counteract sleepiness, any causal link with changes in melatonin output seem tenuous.

Adult↗
PubMed1988

Effects of experimental diabetes on rat hepatic phenylalanine hydroxylase in vivo.

1. The stimulated levels of phenylanine hydroxylase activity in liver extracts from streptozotocin-induced diabetic rats (Donlon and Beirne, 1982) have been correlated with an increased rate of phenylalanine catabolism in vivo. 2. The levels of hepatic phenylalanine hydroxylase protein in diabetic rats become elevated. This effect is not seen in diabetic animals concurrently treated with insulin. 3. The rate of synthesis of liver phenylalanine hydroxylase in 5-day diabetics is 260% that of control animals. 4. These observations are discussed with reference to the regulation of hepatic phenylalanine hydroxylase and phenylanine metabolism in rats.

Animals↗
PubMed1988

AIDS response.

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Acquired Immunodeficiency Syndrome↗
PubMed1985

Purification and characterization of two aminopeptidases from guinea-pig small-intestinal mucosa. Cavian intestinal tripeptide hydrolases.

Two electrophoretically distinct cytosolic peptide hydrolases from guinea-pig small-intestinal mucosa have been highly purified by a six-step procedure comprising extraction from mucosal homogenate, ammonium sulphate fractionation, DEAE-cellulose chromatography, chromatofocusing, calcium phosphate chromatography and Sephadex G-100 gel filtration. They have similar apparent molecular masses as determined by gel filtration (Mr = 68 000) or by sodium dodecyl sulphate gel electrophoresis (Mr = 72 000). Both are aminopeptidases with optimum activity at pH 7.6. They are strongly inhibited by p-hydroxymercuribenzoate, o-phenanthroline and bestatin. Although both hydrolyse some dipeptides they have a distinctive kinetic preference for tripeptides composed of aromatic or non-polar residues. Their affinities for some tripeptides are particularly high and also the hydrolysis of some substrates exhibits biphasic kinetics. These two aminotripeptidases are similar but they can be differentiated from each other and from a number of other aminopeptidases.

Aminopeptidases↗
PubMed1985

Effect of glucagon on hepatic phenylalanine hydroxylase in vivo.

Moderate doses of glucagon (20 micrograms/kg I.V.) are sufficient to stimulate rat hepatic phenylalanine hydroxylase in vivo. In addition, the stimulation of the tetrahydrobiopterin-dependent phenylalanine hydroxylase activity in livers of animals fed on a high-protein diet has been correlated with an elevated phosphate content. The tetrahydrobiopterin-dependent hydroxylase activity in these animals can be further elevated by glucagon-stimulated phosphorylation. These results indicate that physiological changes in glucagon concentration modulate rat liver phenylalanine hydroxylase activity in vivo. The current understanding of the role of phosphorylation in regulating human phenylalanine hydroxylase is also considered.

Animals↗
PubMed1979

Characterization of an RNA-directed DNA-polymerase from a cell line derived from a radiation-induced lymphoma in mice.

An RNA-directed DNA polymerase was purified from a cell line derived from a radiation-induced lymphoma in NIH Swiss mice which produced non-infectious type C virus particles. The enzyme was isolated from a high speed particulate fraction which bands at a density of 1.16--1.19 g/ml in a sucrose gradient, and purified by successive chromatography on DEAE-cellulose, phosphocellulose and hydroxyapatite. The purified DNA polymerase has a molecular weight of 68 000, a pH optimum of 7.5, a KCl optimum of 50 mM, and a Mn2+ optimum of 0.25 mM. It prefers (dT)15 . (A)n to (dT)15 . (dA)n as the primer template and transcribes the poly(C) strand of (dG)15 .(C)n and (dG)15 . (OMeC)n. It transcribes heteropolymeric regions of avian myeloblastosis virus 70 S RNA, and is inhibited by antiserum to Rauscher murine leukemia virus DNA polymerase. Comparison of the properties of DNA polymerase purified from radiation-induced lymphoma cells with the DNA polymerase purified from non-defective murine type C RNA tumor viruses shows that the mouse lymphoma enzyme is both biochemically and immunologically related to murine leukemia virus DNA polymerases.

Animals↗
PubMed1978

Glucagon stimulation of rat hepatic phenylalanine hydroxylase through phosphorylation in vivo.

Phenylalanine hydroxylase activities in extracts of livers from rats pretreated with glucagon are higher than in controls. This time-dependent activation is seen when the hydroxylase is assayed in the presence of tetrahydrobiopterin, but not in the presence of 2-amino-4-hydroxy-6,7-dimethyltetrahydropterin. A maximum 4-fold stimulation of hydroxylase activity was correlated with a conversion of the multiple forms of the enzyme to a single form. This form is characterized by an increased extent of phosphorylation compared to the unactivated enzyme. Incorporation of radioactive inorganic phosphate into phenylalanine hydroxylase following administration of glucagon was determined after specific immunoprecipitation of the enzyme from partially purified preparations. Sodium dodecyl sulfate disc gel electrophoresis showed that stimulation of enzyme activity is accompanied by incorporation of 32Pi into the protein to the extent of 0.7 mol/mol of hydroxylase subunit. These results demonstrate the phosphorylation of hepatic phenylalanine hydroxylase in vivo and strongly support the idea that the activity of this enzyme can be hormonally regulated through a phosphorylation mechanism.

Animals↗