PubMed Health⌕ Search

Biomedical subjects

W de Boer

Publications and source records attributed to W de Boer.

49 records · Page 3Linked to original sources
PubMed1981

Cell wall metabolism in Bacillus subtilis subsp. niger: accumulation of wall polymers in the supernatant of chemostat cultures.

Cell wall polymers were measured both in the cells and in the cell-free medium of samples from steady-state chemostat cultures of Bacillus subtilis, growing at various rates under magnesium or phosphate limitation. The presence of both peptidoglycan and anionic wall polymers in the culture supernatant showed the occurrence of wall turnover in these cultures. Variable proportions of the total peptidoglycan present in the culture samples were found outside the cells in duplicate cultures, indicating that the rate of peptidoglycan turnover is variable in B. subtilis. Besides peptidoglycan, anionic wall polymers were detected in the culture supernatant: teichoic acid in magnesium-limited cultures and teichuronic acid in phosphate-limited cultures. In several samples, the ratio between the peptidoglycan and the anionic polymer concentrations was significantly lower in the extracellular fluid than in the walls. This divergency was attributed to the occurrence of direct secretion of anionic polymers after their synthesis.

Bacillus subtilis↗
PubMed1979

The role of ligand-binding as a determinant of the structure and activation of the estrogen receptor.

The dissociation of estradiol from the estrogen receptor occurs in two kinetic phases: a fast component having a half-time of approximately 3 min and a slower, or second, dissociating component having a half-time of approximately 95 min at 28 degrees. The fast component is produced by the dissociation of estradiol from the nonactivated 4 S receptor, a monomer. Thus, the magnitude of the fast component of the [3H] estradiol biphasic dissociation curve is proportional to the fraction of the receptor in the nonactivated state. The slow component is the estradiol dissociating from the activated 5 S receptor, a dimer. The salt-extracted estrogen receptor isolated from uterine nuclei shows a single, slow dissociating component equal to the slower component of the cytoplasmic biphasic dissociation curve. Estradiol binding shifts the receptor equilibrium from the low affinity nonactivated 4 S receptor toward the high affinity activated 5 S receptor. The kinetics of estriol dissociation from the receptor shows a larger fractional magnitude for the fast component and a faster second dissociating component than estradiol. This suggests that estriol transforms a smaller fraction of the receptor to the activated state and that the activated estriol receptor has a shorter half-time than estradiol. The biphasic dissociation kinetics of an estrogen from the receptor provides a new and sensitive criterion for measuring receptor activation.

Animals↗
PubMed1978

Oestradiol-receptor complexes in subnuclear fractions of rat uterine tissue.

The subnuclear distribution of 3H-oestradiol-receptor complexes was studied in uterine tissue of ovariectomized adult rats. Nuclei were sonically disrupted and 8 different subnuclear fractions were isolated by discontinuous sucrose density gradient centrifugation. 3H-Oestradiol-receptor complexes, measured by hydroxylapatite column chromatography, were localized in a light chromatin fraction as well as in a heavy chromatin fraction. Using the hydroxylapatite chromatography technique it was possible to demonstrate three classes of oestradiol-receptor complexes which differ in affinity for the chromatin. Oestradiol-receptor complexes with a high affinity for the chromatin were predominantly localized in the heavy chromatin fraction, whereas complexes with a lower affinity for their acceptor sites were present in the lighter chromatin fraction.

Animals↗
PubMed1977

Comparative study of nuclear binding sites for oestradiol in rat testicular and uterine tissue. Determination of low amounts of specific binding site by an [3H] oestradiol-exchange method.

1. An [3H]oestradiol-exchange method was developed for the determination of oestradiol-receptor complexes in the nuclear fraction of immature rat testicular tissue. This method permits the determination of nuclear oestradiol-receptor sites in the presence of a relatively large amount of non-specific oestradiol binding present in testicular nuclei. After incubation of nuclei for 60min at 20 degrees C in the presence of [3H]oestradiol with or without a 1000-fold excess of non-radioactive diethylstilboestrol, specific binding can be determined quantitatively in the KCl-extractabe fraction, which contains 40% of the total receptor population. 2. The amount of receptor-bound steroid present in the 0.4m-KCl extract of testicular neclei remained constant during incubation at 20 degrees C. For uterine nuclei incubated with [3H]oestradiol at 37 degrees C a shift of specifically bound [3H]oestradiol occurred from the KCl-soluble fraction to the KCl-insoluble fraction. 3. In intact rat testis, about 20% of the total receptor concentration was present in its nuclear form. Hypophysectomy 5 days before measurement resulted in a twofold decrease in the amount of receptor, which was present mainly in the cytosol. After injection of choriogonadotropin to intact animals, the total receptor concentration increased threefold. 4. This nuclear exchange method might be useful for determination of occupied specific receptor sites in tissues with relatively low contents of specific receptors.

Animals↗
PubMed1976

Effects of oestradiol-18beta, hypophysectomy and age on cytoplasmic oestradiol-17beta receptor sites in rat testis interstitial tissue.

After administration of oestradiol-17beta to intact mature and immature rats, a decrease in the testicular concentration of specific oestradiol-binding sites was observed within 1 h. The binding capacity was replenished starting about 3 h after oestradiol administration and after 5 h the oestrogen receptor level had returned to control values. Exposure of intact animals to oestradiol-17beta for longer periods (up to 24 h) did not result in an increase of receptor levels in testicular cytosol. Mature animals which were hypophysectomized for periods of up to 10 days did not show a significant change in the number of specific oestradiol-binding sites in either total testicular tissue or dissected interstitial tissue. At 15 days or longer periods after hypophysectomy, an apparent increase in receptor concentrations in total testicular cytosol was observed due to a relative increase in the amount of interstitial tissue. A specific oestradiol-binding protein is present in plasma of immature male rats aged less than 30 days. This plasma protein could also be demonstrated in the cytosol of testes of immature rats. In contrast to the cytosol receptor, which shows a moderate affinity for diethylstilbestrol (DES), the plasma protein did not bind DES. The sedimentation values of the plasma protein and the oestradiol receptor were 4 S and 8 S respectively. These differences in characteristics made it possible to demonstrate the presence of the oestradiol receptor in addition to the binding protein in testicular cytosol of rats from 14 days of age onwards. The nuclear receptor for oestradiol-17beta could be demonstrated after incubation of testicular tissue of rats from 4 days of age onwards.

Age Factors↗
PubMedDate not supplied

The relationship between posture and curvature of the cervical spine.

OBJECTIVE: To study the relationship between posture and curvature of the cervical spine in healthy subjects. SUBJECTS: The study was composed of 54 healthy students (25 men and 29 women) aged 20-31 yr with a mean age of 24.7 yr. METHODS: Lateral radiographs were taken of the head and cervical spine of the subjects while standing in a neutral position. Cervical spine posture was quantified by the angle of a reference line, composed of reference points of the upper six cervical vertebrae, with the horizontal axis. The curvature of the cervical spine was classified visually as lordotic, straight or reversed. RESULTS: A relationship was found between posture and curvature of the cervical spine (p = .006); a more forward posture of the cervical spine was related to a partly reversed curvature; and a more upright posture was related to a lordotic curvature. Moreover, men more often exhibited a straight curvature, and women more often exhibited a partly reversed curvature. CONCLUSION: The curvature of the cervical spine is related to the subject's posture and gender.

Adult↗