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Biomedical subjects

M Cross

Publications and source records attributed to M Cross.

At least 217 records · Page 12Linked to original sources
PubMed1988

Expression of the E.coli hemolysin secretion gene hlyB involves transcript anti-termination within the hly operon.

The genes hly A and hly B dictating synthesis and secretion of hemolytic toxin by Escherichia coli are transcribed as part of an operon hly C, hly A, hly B but are separated by an inverted repeat and poly-T sequence characteristic of a rho-independent terminator. The hly A-hly B intergenic sequence caused a reduction of in vivo transcriptional read-through from the gal promotor into gal K when inserted in the pKG1900 terminator-probe vector and also in vitro 3' to the bacteriophage T7 luminal diameter 10 promotor. Hybridisation of mRNA generated by the hly determinant of recombinant DNA pBR202-312 to an antisense RNA probe spanning the hly intergenic sequence revealed specific termination of 80% of in vivo hly transcripts within the poly-T sequence, immediately preceding the hly B translation start. Extension of the hly determinant with 3.5kbp of hly promotor-proximal DNA sequence raised intracellular and cell-free hemolytic activity 3-fold and 20-fold respectively and increased markedly the secretion of the 107Kd hemolysin protein (HlyA). Parallel hybridisation of in vivo mRNA to hly A and hly B antisense probes revealed that levels of hly A and hly B mRNA were increased by approximately 3-fold and 90-fold. The dramatically enhanced level of hly B mRNA resulted primarily from specific suppression of transcription termination at the intergenic rho-independent terminator from 80% to 1%, thus allowing virtually all hly A transcripts to elongate into hly B.

Bacterial Proteins↗
PubMed1988

Mouse lysozyme M gene: isolation, characterization, and expression studies.

We have isolated and characterized both cDNA and genomic DNA of the mouse lysozyme M gene. Derivation of the amino acid sequence from the nucleotide sequences revealed six positions in the carboxyl terminus that differ from partial sequences previously published. The differential detection of specific mRNAs from the closely related lysozyme M and P genes has revealed different but overlapping tissue specificities of expression. The M gene is expressed weakly in myeloblasts, moderately in immature macrophages, and strongly in both mature macrophages and macrophage-rich tissues, while high levels of P transcripts are present only in small intestine. Sites of protein accumulation, rather than gene expression, have been identified by comparative quantitation of mRNA and enzyme levels.

Amino Acid Sequence↗
PubMed1987

Plasma oxipurinol concentrations during allopurinol therapy.

The plasma concentrations of oxipurinol, the chief metabolite of allopurinol, were studied in 66 patients with gout in whom the dose of allopurinol varied between 100 and 400 mg per day. Renal function ranged from normal to moderately impaired. Plasma oxipurinol concentrations correlated directly with both allopurinol dosage and with renal glomerular function as reflected by the plasma creatinine concentration. Plasma oxipurinol concentrations between 30 and 100 mumol/l were generally effective in controlling hyperuricaemia. However, oxipurinol concentrations usually rose above this range if the daily dose of allopurinol exceeded 300 mg in patients with plasma creatinine concentrations of 0.2 mmol/l or more. In patients with normal renal function, a rise of the plasma xanthine concentration to between 6 and 9 mumol/l suggested a satisfactory degree of xanthine oxidase inhibition. These measurements are particularly useful in patients who are still hyperuricaemic despite the usual doses of allopurinol.

Allopurinol↗
PubMed1987

The secreted hemolysins of Proteus mirabilis, Proteus vulgaris, and Morganella morganii are genetically related to each other and to the alpha-hemolysin of Escherichia coli.

Secreted hemolysins were extremely common among clinical isolates of Proteus mirabilis, Proteus vulgaris, and Morganella morganii, and hemolytic activity was either cell associated or cell free. Southern hybridization of total DNA from hemolytic isolates to cloned regions of the Escherichia coli alpha-hemolysin (hly) determinant showed clear but incomplete homology between genes encoding production of hemolysins in the four species. One of the two E. coli secretion genes, hlyD, hybridized only with DNA from P. vulgaris and M. morganii, which produced cell-free hemolysis, but not with that from P. mirabilis, which showed only cell-associated activity. Molecular cloning of the genetic determinants of cell-free hemolytic activity from P. vulgaris and M. morganii chromosomal DNA allowed their functional analysis via inactivation with the transposons Tn1000 and Tn5. Both hemolysin determinants were about 7.5 kilobase pairs and comprised contiguous regions directing regulation, synthesis, and specific secretion out of the cell. Transposon mutations which eliminated secretion of the Proteus and Morganella hemolysins could be complemented specifically by the E. coli hemolysin secretion genes hlyB or hlyD. Alignment of the physically and functionally defined hly determinants from P. vulgaris and M. morganii with that of the E. coli alpha-hemolysin confirmed a close genetic relationship but also indicated extensive evolutionary divergence.

Bacterial Proteins↗
PubMed1986

A preliminary report on the effects of parasitism by the leeches Theromyzon cooperi and Placobdella garoui on the physiology of the redbilled teal Anas erythrorhyncha.

The effects of parasitism by leeches Theromyzon cooperi and Placobdella garoui on the redbilled teal Anas erythrorhyncha were investigated. Leeches with initial body mass ranging from 5.2 to 28.4 mg were allowed to parasitize redbilled teal clamped in Perspex containers. Theromyzon cooperi increased its body mass after parasitism with a mean of 10.5-fold compared to 6.9-fold for P. garoui. Changes were also observed in values of various haematological and biochemical variables of the redbilled teal monitored during this investigation.

Animals↗
PubMed1984

Physiological concentrations of L-leucine control the release of prolactin from cultured rat pituitary cells.

In an attempt to further define the optimum experimental conditions for the in vitro study of PRL endocrinology, the effect of extracellular leucine concentration on PRL secretion was assessed. Rat pituitary cells, maintained in short term monolayer culture, were washed free of serum and placed in Minimum Essential Medium (MEM; 0.39 mM leucine) supplemented with nonessential amino acids and 0.1% gelatin. After the establishment of a constant rate of basal PRL release, the MEM was replaced with leucine-free MEM (supplemented as above), and the rate of PRL release was followed. PRL release from the cells in the leucine-free medium fell within 15 min to a rate 30% of that seen in the controls. Return to the control rate was achieved by the addition of L-leucine only. The D-isomer, isoleucine, valine, proline, leucyl-leucine, and leucine-agarose were ineffective. In the short term, the rate of PRL synthesis was found to be independent of extracellular leucine and the inhibition of release seen upon removal of leucine, and the subsequent recovery upon replacement of leucine was also observed when this experiment was conducted in the presence of 50 micrograms/ml cycloheximide. The L-leucine recovery was found to be dose dependent, with an increase in leucine concentration from 20 to 40 mg/liter causing a tripling of the PRL release rate. The addition of 10(-7) M TRH showed that leucine can be limiting in the response to this stimulant and allowed a response to as little as 10 mg/liter leucine to be discerned. From these experiments, it is concluded that physiological concentrations of leucine specifically and profoundly affect the release of PRL by a mechanism independent of protein synthesis. This leucine requirement for release has not been previously reported.

Animals↗
PubMed1984

The painful knee.

The painful knee is discussed in the context of being the presenting symptom and a structured approach to diagnosis is offered. Mechanism of the pain is defined and related to the common clinical conditions. Diagnosis is essential to management and is possible in most instances with the aid of arthrography and arthroscopy.

Adolescent↗
PubMed1983

Inner-city residents, ethnic minorities and primary health care.

Ethnic minorities form a substantial proportion of the urban population. A household survey in the West Midlands assessed usage of primary and preventative health care services. Asian households made some-what higher use of general practitioner (GP) facilities which can be related to demographic and socio-economic status. Fewer differences were found than expected, and uptake of preventative services was good. Afro-Caribbean patterns were similar to those of whites.

Adolescent↗
PubMed1978

Activity and subcellular distribution of mouse uterine alkaline phosphatase during pregnancy and pseudopregnancy.

The biochemical assay of alkaline phosphatase in the uterus of mice revealed a 13-fold increase in the activity of the enzyme during the peri-implantation period with a relatively short-lived maximum being reached on Day 7 of pregnancy. A similar increase in the activity of the enzyme occurred between Days 5 and 7 of pseudopregnancy in uterine horns of mice receiving a deciduoma-inducing stimulus on Day 4. The presence of factors in uterine homogenates which could possibly modify the activity of the enzyme could not be detected. Low and unaltered levels of alkaline phosphatase activity were found in the blood serum of mice between Days 1 and 10 of pregnancy, suggesting that no appreciable entry of the uterine enzyme into the circulation occurs in this species. Alkaline phosphatase activity in the uterine homogenates was associated with particulate fractions sedimented during centrifucation at at 500, 10,000 and 105,000 g, and only about 29% of the activity was associated with the cytosol fraction. The subcellular distribution of the enzyme activity was the same in decidualized and non-decidualized horns. The association of the enzyme with the particulate material in uterine cells was considered to involve lipoprotein membranes because treatment of homogenates with 0.2% (v/v) Triton X-100 solubilized the enzyme without affecting its catalytic activity.

Alkaline Phosphatase↗