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R Parsons

Publications and source records attributed to R Parsons.

At least 109 records · Page 6Linked to original sources
PubMed1987

The T-antigen-binding domain of the simian virus 40 core origin of replication.

The simian virus 40 origin of replication contains a 27-base-pair palindrome with the sequence 5'-CA-GAGGC-C-GAGGC-G-GCCTC-G-GCCTC-TG-3'. The four 5'-GAGGC-3'/5'-GCCTC-3' pentanucleotides are known contact sites for simian virus 40 T-antigen binding in vitro. We used oligonucleotide-directed cassette mutagenesis to identify features of this palindrome that are important for the initiation of DNA replication in vivo. Each base pair of a pentanucleotide is crucial for DNA replication. In contrast, sequences adjacent to pentanucleotides have little or no effect on replication. Thus, the pentanucleotide is the basic functional unit, not only for T-antigen binding but also for DNA replication. All four pentanucleotides are indispensable in the initiation process. The spacing of pentanucleotides is crucial because duplication of the single base pair between binding sites has a far greater effect on replication than does substitution of the same base pair. Inversion of any pentanucleotide blocks DNA synthesis. Thus, the pentanucleotide is not a functionally symmetrical unit. We propose that each pentanucleotide positions a monomer of T antigen at the proper distance, rotation, and orientation relative to other T-antigen monomers and to other origin domains and that such positioning leads to subsequent events in replication.

Antigens, Polyomavirus Transforming↗
PubMed1986

The side-chain cleavage of cholesterol sulfate--III. The effect of adrenodoxin, membrane phospholipids and Tween 80 on the kinetics of oxidation of the sterol sulfate by a reconstituted cholesterol desmolase system.

This paper reports the Km values of a reconstituted cholesterol side-chain cleavage system for cholesterol sulfate, cholesterol, and adrenodoxin, determined under several experimental conditions. The Km values for adrenodoxin change depending on whether cholesterol or its sulfate is used as the substrate. Moreover, the Km values for both of the substrates and for adrenodoxin are greatly modulated by both membrane phospholipids, isolated from adrenal mitochondria, and Tween 80, 0.002%. In the absence of detergents or phospholipids, the enzyme system shows a high affinity for cholesterol sulfate, but is inhibited when high concentrations of the sterol sulfate are added to the incubation mixture. Raising the concentration of adrenodoxin in the assay mixture prevents the substrate inhibition. When cholesterol sulfate is incorporated into micelles containing the phospholipids, the enzyme system does not display substrate inhibition, and the kinetics of cleavage of the sterol sulfate are relatively independent of the concentration of adrenodoxin in the assay mixture. In the absence of phospholipids, the apparent kinetics of cleavage of cholesterol and its sulfate are quite different from each other, but when incorporated into micelles containing phospholipids, the kinetics of cleavage of the two substrates are similar to each other.

Adrenal Cortex↗
PubMed1985

The side-chain cleavage of cholesterol sulfate--II. The effect of phospholipids on the oxidation of the sterol sulfate by inner mitochondrial membranes and by a reconstituted cholesterol desmolase system.

This study compares the side-chain cleavage of aqueous suspensions of cholesterol sulfate with the side-chain cleavage of cholesterol sulfate which is incorporated into phospholipid vesicles. Three different cholesterol desmolase systems are examined: the membrane-bound cholesterol side-chain cleavage system present in inner mitochondrial membranes isolated from bovine adrenal mitochondria; a soluble, lipid-depleted, reconstituted side-chain cleavage system prepared from cytochrome P-450scc, adrenodoxin and adrenodoxin reductase; a membrane associated side-chain cleavage system prepared by adding phospholipid vesicles, prepared from adrenal mitochondrial, to the reconstituted system. Soluble cholesterol sulfate, in low concentration, is a good substrate for the lipid-depleted reconstituted side chain cleavage system. However, at concentrations above 2 microM, in the absence of phospholipids, the sterol sulfate appears to bind at a non-productive site on cytochrome P-450scc which leads to substrate inhibition. Phospholipids, while inhibiting the binding of cholesterol sulfate to the cytochrome, also appear to prevent non-productive binding of the sterol sulfate to the cytochrome. Thus the addition of phospholipids to the lipid-depleted enzyme system leads to an activation of side-chain cleavage of high concentrations of the sterol sulfate. Soluble cholesterol sulfate is a good substrate for both the native and reconstituted membrane-bound systems and no substrate inhibition is observed when the membrane bound enzyme systems are employed in the assay of side-chain activity. However, the cleavage of cholesterol sulfate, which is incorporated into phospholipid vesicles, by both membrane bound enzyme systems appears to be competitively inhibited by the phospholipids of the vesicles. The results of this study suggest that the regulation of the side-chain cleavage of cholesterol sulfate may be entirely different than the regulation of the side-chain cleavage of cholesterol, if cholesterol sulfate exists intracellularly as a soluble non-complexed substrate. If, on the other hand, cholesterol sulfate is present in the cell in lipid droplets as a complex with phospholipids, its metabolism may be under the same constraints as the side-chain cleavage of cholesterol.

Adrenal Glands↗
PubMed1984

The pathogenic properties of Fusobacterium and Bacteroides species from wallabies and other sources.

Intracerebral inoculation was more effective than intraperitoneal, intravenous or subcutaneous inoculation as a means of producing lethal infections with Fusobacterium necrophorum in mice. Strains varied in virulence but, of five examined, two had LD50 values as low as ca. 8000 and 14000 viable organisms. Profuse bacterial multiplication in the brain was demonstrated. Intravenous vaccination with a single large dose of heat-killed whole culture or washed bacterial cells failed to protect against intracerebral challenge. Intracerebral injection of other fusobacteria (F. nucleatum, F. varium and F. necrogenes) and of 22 strains belonging to 10 Bacteroides spp. was without apparent effect on mice, except for a slight transient illness in some animals given B. fragilis. This organism (five strains) differed from the other Bacteroides spp. tested, which included eight strains belonging to the fragilis group, in being eliminated more slowly from the mouse brain--a point that may be relevant to the special pathogenicity of B. fragilis in endogenous infections in man. There was no evidence that B. fragilis multiplied in the brain or that intravenous vaccination with a large dose of heat-killed homologous culture affected the rate at which it was eliminated.

Animals↗
PubMed1984

Aetiological agents of necrobacillosis in captive wallabies.

In a series of 27 wallabies (Macropus rufogriseus) with necrobacillosis, 14 animals were affected in the face, nine in the leg and six in the internal organs, two being affected in more than one site. Fusobacterium necrophorum was the predominating organism, occurring in 69 per cent of lesions, usually in heavy and occasionally in pure culture. Bacteroides species (six in all), often in considerable numbers, were found in 48 per cent of lesions, and F nucleatum in 14 per cent. Aerobes or facultative anaerobes, usually in small numbers, were present in 59 per cent of lesions. The organisms isolated often varied considerably from one part of the lesion to another.

Animals↗
PubMed1983

Mixed bacterial infection of the pericardium.

Polymicrobic bacterial infection of the pericardium was detected in a 59-year-old patient ultimately proven to have esophageal carcinoma. Such infections are becoming more frequent, often combine gram-negative bacilli and anerobes, and may be deceptively mild clinically. Origin from an occult head and neck or gastrointestinal focus rather than from pulmonary (pneumococcal) or distant (staphylococcal) sources distinguishes these infections. Newer diagnostic techniques (computerized tomography and echocardiography) coupled with surgical drainage and appropriate antibiotic therapy may improve the current 67% mortality.

Anti-Bacterial Agents↗
PubMed1979

A simple method for incorporating single pass dialysate delivery and controlled ultrafiltration with the RP-6 high flux dialyzer.

A simple hemodialysis protocol has been developed to permit significant "middle molecule" clearance, yet retain normal low molecular weight clearance. The high flux RP-6 dialyzer has been combined with a single pass dialysate delivery system to provide accurate control of ultrafiltration without resorting to specialized or expensive equipment. By operating the RP-6 in the co-current mode, a simple valve on the dialysate output can be used to regulate ultrafiltration. At QB = 200 ml/min and QD = 500 ml/min, CU = 127 ml/min and CB12 = 56 ml/min at zero ultrafiltration rate; these values increase considerably with ultrafiltration. This protocol offers dialysis centers with standard equipment the opportunity to use high flux membranes in a routine manner.

Animals↗
PubMed1978

Ultrastructural evidence of "abortive" regeneration in murine muscular dystrophy.

Triceps and gastrocnemius muscles from dystrophic (129 ReJ dy/dy) and normal mice were examined by electron microscopy at different stages in development (birth to 6 months). A qualitative assessment was made of the incidence and success of regeneration. Mitotic figures were seen in satellite cells in two-week-old dystrophic muscle. Well-differentiated myotubes were seen in dystrophic muscles at all ages but the incidence of regeneration was greatly reduced in the older dystrophic muscles. Myotubes in areas of regeneration up to two months of age frequently showed atypical or degenerative features. It is concluded that regeneration of dystrophic mouse muscle proceeds normally to the myotube stage after which differentiation becomes aberrant and degeneration may occur. This "abortive" regeneration probably contributes to the progression of the myopathy.

Animals↗
PubMed1978

A quantitative assessment of the effect of medium composition on mouse myogenesis in vitro.

The effect of variations in medium horse serum (HS) and chick embryo extract on the extent of myogenesis in primary mouse muscle cultures was investigated. Seeding efficiency at 24 h in culture did not vary with medium composition, but total cell number at 8 days was diminished at low embryo extract concentrations. Five media from the range of 16 tested, supported significantly greater myogenesis. Within this group of 5, there was no difference in ability to support myogenesis. The effect of medium composition on myogenesis is discussed.

Cell Count↗
PubMed1978

Hyper/hypo-osmotic peritoneal dialysis.

This report concerns the augmentation of peritoneal dialysis using alternating hyper/hypoosmotic peritoneal dialysates, and covers a detailed examination of the longest lived, anephric goat to be maintained using this delivery system. Experimental results show that with this technique: 1) urea clearance can be increased some 200% over control values, 2) the convective transport of urea is unimportant and the increased urea clearance is due primarily to increased peritoneal permeability, 3) net ultrafiltration and electrolyte balance can be easily controlled by variation of total electrolyte and glucose about an appropriate mean. A detailed autopsy failed to demonstrate any gross or microscopic pathology.

Abdomen↗