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V Cameron

Publications and source records attributed to V Cameron.

At least 19 recordsLinked to original sources
PubMed2006

The astrobiology primer: an outline of general knowledge--version 1, 2006.

The Astrobiology Primer has been created as a reference tool for those who are interested in the interdisciplinary field of astrobiology. The field incorporates many diverse research endeavors, but it is our hope that this slim volume will present the reader with all he or she needs to know to become involved and to understand, at least at a fundamental level, the state of the art. Each section includes a brief overview of a topic and a short list of readable and important literature for those interested in deeper knowledge. Because of the great diversity of material, each section was written by a different author with a different expertise. Contributors, authors, and editors are listed at the beginning, along with a list of those chapters and sections for which they were responsible. We are deeply indebted to the NASA Astrobiology Institute (NAI), in particular to Estelle Dodson, David Morrison, Ed Goolish, Krisstina Wilmoth, and Rose Grymes for their continued enthusiasm and support. The Primer came about in large part because of NAI support for graduate student research, collaboration, and inclusion as well as direct funding. We have entitled the Primer version 1 in hope that it will be only the first in a series, whose future volumes will be produced every 3-5 years. This way we can insure that the Primer keeps up with the current state of research. We hope that it will be a great resource for anyone trying to stay abreast of an ever-changing field.

Astronomical Phenomena↗
PubMed2001

Second-site, intragenic alterations in the gene encoding subunit II of cytochrome c oxidase from yeast can suppress two different missense mutations.

Cytochrome c oxidase, a multi-subunit enzyme complex, accepts electrons from cytochrome c and transfers them to molecular oxygen to form water. Subunit II (Cox2p) of the enzyme complex provides the initial entry site for the electrons from cytochrome c. We report here the characterization of a yeast strain bearing a mutation in the gene encoding Cox2p which abolishes the activity of the enzyme complex. The alteration, at residue 163 in the yeast polypeptide, substitutes isoleucine for threonine and leads to loss of Cox2p and loss of the ability to carry out cellular respiration. We have also characterized 55 independent revertants of the mutant which have recovered the ability to respire. Of these revertants, 37 recover the ability to respire due to a compensatory alteration at residue 163, which produces either a wild-type threonine codon or one for valine or serine. The other 18 revertants recover function due to secondary changes at four different codons within the gene encoding Cox2p. Some of these second-site, intragenic revertants occur at sites significantly distant from the position of the original mutation. In addition, alterations at two of these sites have previously been shown to suppress a completely different missense mutation in the gene.

Amino Acid Sequence↗
PubMed1999

Analysis of strains of Saccharomyces cerevisiae with amino acid substitutions in the Cu(A)-binding region of subunit II of cytochrome c oxidase.

Cytochrome c oxidase accepts electrons from cytochrome c and transfers them to oxygen to form water. Electrons enter the complex through the Cu(A) site, formed by two copper atoms bound to mitochondrially encoded subunit II. The effect of amino-acid alterations in one of the Cu(A) ligands and in an amino acid adjacent to another of the ligands in the yeast enzyme is examined. Substitution of tyrosine for the Cu(A) ligand, cysteine 221, completely abolishes enzyme activity. In addition, 19 independent revertants of this mutant yeast strain recover function by restoring the cysteine codon. Replacement of a non-conserved glycine at position 228 by valine, adjacent to the Cu(A)-ligand histidine 229, virtually blocks enzyme activity. Activity is restored by inserting alanine or phenylalanine at position 228 or by amino-acid substitutions at nearby codons. Our results demonstrate that the Cu(A) ligand appears to be essential for enzyme function while other residues in the copper-binding region are less functionally constrained.

Amino Acid Sequence↗
PubMed1996

The effect of amino acid substitutions in the conserved aromatic region of subunit II of cytochrome c oxidase in Saccharomyces cerevisiae.

Mitochondrial encoded subunit II of cytochrome c oxidase carries the metal center, which acts as the initial acceptor of electrons from cytochrome c. Among the conserved features of this protein is a region in which five aromatic and three non-aromatic amino acids are conserved in a wide variety of organisms. This aromatic region has been postulated to be involved in transfer of electrons from the copper center in subunit II to the remaining metal centers of cytochrome oxidase in subunit I. To test the functional importance of two conserved, aromatic tryptophan residues and one conserved, non-aromatic glycine residue, yeast strains with alterations at these positions were characterized. The strains with altered codons were tested for their ability to carry out cellular respiration, for their growth rates on non-fermentable carbon sources, and for their cytochrome c oxidase activity. The results demonstrate that the aromatic character of the tryptophan residues appears necessary for subunit II function, while the conserved glycine can be replaced with other, small, uncharged residues.

Amino Acid Sequence↗
PubMed1994

Replacement of a conserved glycine residue in subunit II of cytochrome c oxidase interferes with protein function.

In this paper we describe the isolation and characterization of a respiration-deficient yeast strain which is defective in the function of subunit II of cytochrome c oxidase. This strain, VC32, carries a mutation in the mitochondrial COX2 gene which converts a conserved glycine residue to arginine. The conserved glycine is in a region implicated as important for ligating the CuA redox center and for interaction with cytochrome c. We have also characterized five revertants of VC32 which have recovered respiratory function; all five were mapped to the mitochondrial genome. In three of the five revertants the wild-type glycine codon is restored, while in two of the five the mutant arginine codon is still present. These two strains are likely to possess alterations either in components of the mitochondrial translation machinery or in mitochondrially-encoded gene products that interact directly with subunit II to assemble an active oxidase complex.

Amino Acid Sequence↗
PubMed1994

Food for thought.

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Ethics, Medical↗
PubMed1992

Whither medicine?

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Delivery of Health Care↗
PubMed1987

Effect of central naloxone on hormone and blood pressure responses to hemorrhage in conscious sheep.

The role of the brain opioid system in the control of hypothalamic-pituitary-adrenal activity was studied in 10 conscious sheep with an indwelling cannula in a cerebral lateral ventricle. On separate days, sheep received infusions of artificial CSF (control) and the opiate antagonist, naloxone (100 micrograms/hr) before and during acute moderate hemorrhage (15 ml/kg over 10 min). Infusion of naloxone before hemorrhage raised plasma ACTH and resulted in a significant increase in cortisol compared to the control infusion. In contrast, ACTH and cortisol responses to hemorrhage tended to be blunted by central naloxone infusion. The responses of vasopressin, aldosterone and the catecholamines remained unaffected by naloxone. The fall in blood pressure and the rise in heart rate accompanying hemorrhage were likewise unaltered. These results suggest that brain opioid peptides have an inhibitory effect on basal ACTH secretion but do not play a major role in modulating the hemodynamic or pituitary-adrenal responses to acute moderate hemorrhage in conscious sheep.

Adrenocorticotropic Hormone↗
PubMed1987

Effect of metoclopramide on adrenal secretion in sheep: influence of dexamethasone and sodium intake.

Metoclopramide, a competitive dopamine antagonist, stimulates aldosterone in man and monkey without affecting cortisol secretion. In sheep, metoclopramide also stimulates aldosterone but ist action on adrenocortical secretion is more controversial. To clarify the action of metoclopramide in conscious sheep, the response of plasma aldosterone, cortisol, angiotensin II and potassium were studied after 0.16 and 0.64 mg/kg metoclopramide, with and without pretreatment with dexamethasone. The effect of sodium status on the response was also studied by repeating the experiments after 7 days of dietary sodium restriction. In the absence of dexamethasone, plasma aldosterone was significantly increased by metoclopramide in both sodium-replete and restricted sheep. In sodium-replete sheep, plasma cortisol was also increased by 0.64 mg/kg, and by both doses when salt-restricted. However all cortisol responses were completely suppressed by dexamethasone pretreatment. Dexamethasone also suppressed the aldosterone response to metoclopramide in sodium-replete but not in sodium-restricted sheep where significant responses of aldosterone to both doses of metoclopramide still occurred without changes in plasma angiotensin II or potassium. While a nonspecific stress effect of metoclopramide can contribute to the aldosterone response, these results show that the sheep's adrenal glomerulosa is capable of responding to metoclopramide without change in ACTH, angiotensin or potassium.

Adrenal Glands↗
PubMed1987

Acute hemorrhage reduces angiotensin converting enzyme activity in conscious sheep.

When levels of plasma angiotensin converting activity (ACE) were measured in 11 sheep undergoing a 15 ml/kg hemorrhage, levels before hemorrhage (5.7 +/- 0.5 nmol/min/ml) fell significantly at 120 min (3.7 +/- 0.6 nmol/min/ml) and 150 min (3.4 +/- 0.5 nmol/min/ml) after hemorrhage (P less than 0.01). Plasma ACE activity remained constant in ten control sheep studied under the same conditions but not hemorrhaged. The time course of the fall in plasma ACE activity was then studied in an additional four sheep undergoing 15 ml/kg hemorrhage, which reduced mean arterial pressure by 25% at 10 min after hemorrhage. Plasma ACE activity was variable for 60 min post-hemorrhage, but then fell to levels significantly lower than baseline values at 150 min (P less than 0.05). The decrease in plasma ACE activity associated with hemorrhage was small when compared to the effect of an IV infusion of the ACE inhibitor, Captopril (SQ14225, 28 micrograms/min for 3 hr), which reduced plasma ACE activity in the same sheep to almost undetectable levels. These results show that hemorrhage significantly reduces plasma ACE activity in sheep. However, this effect is small and is unlikely to affect the production of plasma AII following acute hemorrhage.

Acute Disease↗