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P Bennett

Publications and source records attributed to P Bennett.

18 recordsLinked to original sources
PubMed1992

Caldesmon binds to smooth muscle myosin and myosin rod and crosslinks thick filaments to actin filaments.

It is well established that caldesmon binds to actin (Kb = 10(7) - 10(-8) M-1) and to tropomyosin (Kb = 10(6) M-1) and that it is a potent inhibitor of actomyosin ATPase. Caldesmon can also bind tightly to myosin. We investigated the binding of smooth muscle and nonmuscle caldesmon isoforms (CDh and CDl respectively) to myosin using proteins from sheep aorta. Both caldesmon isoforms bind to myosin with indistinguishable affinity. The affinity is about 10(6) M-1 in low salt buffer, but is weakened by increasing [KCl] reaching 10(5) M-1 in 100 mM KCl. The stoichiometry of binding is about three caldesmon per myosin molecule. Stoichiometry and affinity are not dependent on whether myosin is phosphorylated nor on the presence of Mg2+ and ATP, provided the ionic strength is maintained constant. The caldesmon binding site of smooth muscle myosin is located in the S-2 region, consequently both HMM and myosin rod bind to caldesmon. Over a range of conditions myosin and myosin rod binding to caldesmon were indistinguishable. Skeletal muscle myosin has no caldesmon binding site. Smooth muscle myosin rods form side-polar filaments in low salt buffer in which the backbone packing of LMM into the filament shaft is clearly visible in negatively-stained electron microscopic images. Sometimes the S-2 portions can be seen 'frayed' from the filament shaft. When caldesmon is bound the filament shaft appears to be about 20% thicker and the frayed effect is dramatically increased; long filamentous 'whiskers' are often seen curving out from the filament shaft. Similar structures are observed with smooth muscle and with non-muscle caldesmon. Myosin also binds to caldesmon when it is incorporated into the thin filament; however, this interaction is qualitatively different. Measurements of smooth muscle HMM binding to native thin filaments in the presence of 3 mM MgATP shows there is a high affinity binding (Kb = 10(6) M-1) which is independent of [Ca2+] and of the level of myosin phosphorylation. The stoichiometry is one HMM molecule per actin monomer which is equivalent to up to 14 HMM bound at high affinity per caldesmon. Negatively stained electron microscopic images of the HMM.ADP.Pi-thin filament complex have failed to show any attachment of HMM to the thin filaments. When rod filaments are added to actin plus caldesmon or to native thin filaments the rod filaments are strongly associated with the actin filament bundles. The majority of rod filaments are lined up parallel and in close proximity to actin filaments.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin Cytoskeleton↗
PubMed1992

Characterization of the chromosomal aac(6')-Ic gene from Serratia marcescens.

The DNA sequence of the chromosomal aac(6')-Ic gene from Serratia marcescens, which had been previously cloned (H. M. Champion, P. M. Bennett, D. A. Lewis, and D. S. Reeves, J. Antimicrob. Chemother. 22:587-596, 1988) was determined. High-pressure liquid chromatographic analysis of extracts prepared from Escherichia coli carrying the chromosomal aac(6')-Ic gene on a plasmid confirmed the presence of 6'-N-acetyltransferase activity in this strain, which was suggested by the aminoglycoside resistance profile. DNA sequence analysis of the cloned 2,057-bp PstI fragment revealed several regions of homology to previously characterized sequences from GenBank, including the rpoD and tRNA-2 genes of E. coli. Subcloning experiments confirmed the coding sequence of the aac(6')-Ic gene to be at positions 1554 to 1992. The predicted amino acid sequence of the AAC(6')-Ic protein suggested that it was the third member of a family of AAC(6') proteins which included a coding region identified between the aadB and aadA genes of Tn4000 and an AAC(6') protein encoded by pUO490, which was isolated from Enterobacter cloacae. Primer extension analysis suggested that the -35 region of the aac(6')-Ic promoter overlapped a large palindromic sequence which may be involved in the regulation of the aac(6')-Ic gene. Hybridization experiments utilizing a restriction fragment from the aac(6')-Ic gene showed that all S. marcescens organisms carried this gene whether or not the AAC(6')-I resistance profile was expressed. Organisms other than Serratia spp. did not hybridize to this probe.

Base Sequence↗
PubMed1992

The contribution of body composition, substrates, and hormones to the variability in energy expenditure and substrate utilization in premenopausal women.

Twenty-four-hour energy expenditure and substrate use were measured by indirect calorimetry in respiration chambers on a fixed physical program and related to body composition and plasma concentrations of various substrates and thermogenic hormones. Fifty premenopausal women with a wide range of body weight were examined in the follicular menstrual phase under weight stable conditions. Most of the variance in the sleeping energy expenditure (82%) was accounted for by two covariates, lean body mass (75%, P less than 0.0001), and fat mass (7%, P less than 0.0001). An additional 6% of the variance in sleeping energy expenditure was accounted for by plasma androstenedione concentration (4%, P = 0.0005) and by free T3 index (2%, P = 0.03). Thus physiological variation among individuals in plasma androstenedione concentration may result in a difference in energy expenditure of 908 kJ/day and the corresponding variation in free T3 index may result in a difference between individuals of 594 kJ/day. Fifty four percent of the variation in carbohydrate oxidation rates was accounted for by 24-h energy balance, and by plasma concentrations of insulin, nonesterified fatty acids, and estradiol. Waist circumference, plasma nonesterified fatty acids, and estradiol concentrations explained 49% of the variance in 24-h lipid oxidation. An obese subgroup of women (n = 27) had significantly higher 24-h energy expenditure, lipid, and carbohydrate oxidation rates than an age-matched normal weight group (n = 16), but the entire group difference in energy expenditure was explained by differences in body composition. We conclude that physiological variations in plasma androstenedione and T3 concentrations contribute to the interindividual variance in energy expenditure of women, and their role is not different in obese women. A positive energy balance and increased insulin action may be mediators of the higher carbohydrate oxidation in obesity, whereas an increased substrate availability seems to bring about the increased lipid oxidation.

Adolescent↗
PubMed1992

The pituitary-gonadal axis in women with benign or malignant ovarian tumors.

The serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), human chorionic gonadotropin (hCG), estradiol, progesterone, androstenedione, testosterone (total and free) and dehydroepiandrosterone sulphate (DHEAS) were investigated prior to surgery in 24 postmenopausal women with benign and 28 postmenopausal women with malignant epithelial ovarian tumors. The serum concentrations of hormones were compared with those of 28 healthy, postmenopausal, age-matched controls. Significantly lower serum FSH levels were demonstrated in women with malignant tumors. No significant differences were found between the groups regarding the serum LH levels. The hCG levels were low in all groups. Regarding progesterone and estradiol levels, low postmenopausal steroid levels were found in all groups examined and no significant differences were demonstrated within the groups. No significant correlations between the levels of estradiol and FSH or progesterone and LH were demonstrated. To exclude a central depression of gonadotropin release mediated by the dopaminergic system we examined the thyroid stimulating hormone (TSH) and prolactin. No differences were found between the groups regarding TSH and prolactin levels. A possible relationship between other hormones/factors produced by the tumor and exerting a negative feedback, either centrally or directly, on the gonadotropin release remains to be investigated. A change in biological activity in the gonadotropins might explain the present findings.

Aged↗
PubMed1992

Serum sex hormones and endurance performance after a lacto-ovo vegetarian and a mixed diet.

Serum sex hormones and endurance performance after a lacto-ovo vegetarian and a mixed diet. Med. Sci. Sports Exerc., Vol. 24, No. 11, pp. 1290-1297, 1992. The effect of a lacto-ovo vegetarian (V) and a mixed, meat-rich (M) diet on the level of serum sex hormones, gonadotropins, and endurance performance of eight male endurance athletes was investigated in a 2 x 6 wk cross-over study. The energy contribution from carbohydrate, fat, and protein was 58%, 27%, and 15% on the V diet and 58%, 28%, and 14 E% on the M diet. For total fasting serum testosterone (T) there was a significant interaction between diet and time (P < 0.01). Thus, the V diet resulted in a lower total T level (13.7, 9.8-32.4 nmol.l-1) (median and range) compared with the M diet (17.4, 11.8-33.5 nmol.l-1). During exercise after 6 wk on the diets total T was also significantly lower on the V than on the M diet (P < 0.05). Serum free testosterone, however, did not differ significantly during the 6 wk dietary intervention periods and neither did serum concentrations of sex hormone binding globulin, dihydrotestosterone, dehydroepiandrosterone sulphate, 4-androstenedione, estrone, estradiol, estrone sulphate, or gonadotropins. Endurance performance time was higher for six and lower for two after the mixed diet compared with the vegetarian diet. This was not significant, however. In conclusion, 6 wk on a lacto-ovo vegetarian diet caused a minor decrease in total testosterone and no significant changes in physical performance in male endurance athletes compared with 6 wk on a mixed, meatrich diet.

Diet↗
PubMed1991

Menopausal age and sex hormones in postmenopausal women with alcoholic and non-alcoholic liver disease.

In order to evaluate age at menopause and serum sex hormone profiles in postmenopausal women with stable chronic liver disease, six non-cirrhotic alcoholics, 13 with alcoholic cirrhosis, eight with non-alcoholic cirrhosis, and 46 healthy controls were studied. In all three groups, patients were significantly (p less than 0.05) younger at the time of natural menopause than controls. Compared to controls, non-cirrhotic alcoholic women had significantly (p less than 0.05) reduced levels of DHAS, significantly (p less than 0.05) more alcoholic cirrhotic women had detectable oestradiol concentrations, elevated concentrations of oestrone and sex hormone binding globulin (SHBG) and reduced levels of 5 alpha-dihydrotestosterone (DHT), while women with non-alcoholic cirrhosis had significantly elevated concentrations of SHBG and reduced levels of oestrone sulphate, DHT, androstenedione and dehydroepiandrosterone sulphate (DHAS) (p less than 0.05). The observed changes may be a consequence of liver disease since similar changes were observed in patients with alcoholic and non-alcoholic liver disease, but an additional effect of alcohol cannot be excluded.

Aged↗
PubMed1991

Sex hormones in postmenopausal women with primary biliary cirrhosis.

To evaluate serum sex hormone profiles in nonalcoholic postmenopausal women with liver disease, 25 women with primary biliary cirrhosis (11 in cirrhotic stage) and 46 healthy controls were studied. The patients had significantly (p less than 0.05) elevated serum concentrations of estrone and androstenedione and significantly (p less than 0.05) lower concentrations of estrone sulfate, dehydroepiandrosterone sulfate and 5 alpha-dihydrotestosterone compared with the 46 controls. Serum concentrations of sex hormone binding globulin, testosterone, non-sex hormone binding globulin-bound testosterone and non-protein-bound testosterone did not differ significantly (p greater than 0.05) between primary biliary cirrhosis patients and controls. Patients in the cirrhotic stage had significantly (p less than 0.05) higher concentrations of sex hormone binding globulin than did controls. Patients in the cirrhotic stage had significantly (p less than 0.05) higher sex hormone binding globulin and estrone sulfate levels compared with noncirrhotic patients with primary biliary cirrhosis. Otherwise, no significant differences were observed between cirrhotic and noncirrhotic patients. The observed changes in steroid concentrations may be a consequence of hepatic dysfunction.

Aged↗
PubMed1979

The effect of repeated intramuscular gonadotrophin-releasing hormone injections on luteinizing hormone, follicle-stimulating hormone, testosterone, oestrogens, dehydroepiandrosterone and dehydroepiandrosterone sulfate in normal men.

The endocrine response to three daily intramuscular injections of 500 microgram LH-RH was measured in 9 normal men during a period of 3 days. A marked but declining response in LH was seen in addition to a significant increase in the serum concentration of FSH, testosterone, oestradiol and the urinary excretion of oestrogenic substances. No change could be demonstrated in the DHA, DHAS or cortisol secretion which confirms our previous results of a direct effect of clomiphene on adrenal steroidogenesis.

Adrenal Cortex↗
PubMed1979

Infant nutrition.

Explore the source record for details and available documents.

Child Advocacy↗
PubMed1977

Correlation between rises of gonadotrophins and rises of sex steroids during clomiphene test in men.

Serum FSH, LH and testosterone and urinary excretion of androsterone, aetiocholanolone, dehydroepiandrosterone and total oestrogens were measured in normal and oligospermic men before and after clomiphene stimulation. Responses in all parameters were highly variably from one individual to another and this great variation formed the basis for investigating the correlations between responses. There was no correlation between increase of FSH and LH or increase of LH and steroids. Also there was no correlation between rises of FSH and rises of androgens. But a significant correlation existed between rises of FSH and rises of oestrogens. This confirms that one action of FSH is to stimulate production of testicular oestrogens which presumably takes place in the Sertoli cells.

Adolescent↗