Biomedical subjects

Q Dong

Publications and source records attributed to Q Dong.

At least 145 records · Page 8Linked to original sources

PubMed1993

Hypothalamo-pituitary gonadal axis in chronic renal failure.

Chronic renal failure causes extensive neuroendocrine disturbance, including marked hypothalamo-pituitary dysfunction which is reversed by renal transplantation but not dialysis. Gonadal dysfunction in uremia is manifest as delayed puberty in adolescents; as testicular atrophy, hypospermatogenesis, infertility, impotence in men; and as anovulation, infertility, and menstrual disturbance in women. Gonadal steroidogenesis and gametogenesis are impaired and gonadotropin levels are increased. In addition to evidence of defects in pituitary and gonadal function, increasing evidence indicates the importance of alterations in hypothalamic regulation of pituitary-gonadal function in the pathogenesis of uremic hypogonadism. Experimental uremia induced by subtotal nephrectomy in mature rats causes gonadal dysfunction, which is principally due to aberrant neuroendocrine regulation of GnRH secretion involving inhibition of GnRH secretion, hypersensitivity to negative testicular feedback, and resistance to naloxone, a triad of features termed ontogenic regression.

Female↗

PubMed1992

Corrected nucleotide sequence of M13mp18 gene III.

There are seven differences between the actual nucleotide (nt) sequence of bacteriophage M13mp18 gene III and the previously reported nt sequence (which had been compiled based on the nt sequence of wild-type bacteriophage M13 gene III).

Amino Acid Sequence↗

PubMed1992

Site-directed mutagenesis of the phosphate-binding consensus sequence in Escherichia coli adenylosuccinate synthetase.

Adenylosuccinate synthetases from different sources contain an N-terminal glycine-rich sequence GDEGKGK, which is homologous to the conserved sequence GXXXXGK found in many other guanine nucleotide-binding proteins or enzymes. To determine the role of this sequence in the structure and function of Escherichia coli adenylosuccinate synthetase, site-directed mutagenesis was performed to generate five mutant enzymes: G12V (Gly12----Val), G15V (Gly15----Val), G17V (Gly17----Val), K18R (Lys18----Arg), and I19T (Ile19----Thr). Comparison of the kinetic properties of the wild-type enzyme and those of the mutant enzymes revealed that the sequence is critical for enzyme activity. Replacement of Gly12, Gly15, or Gly17 with Val, or replacement of Lys18 with Arg, resulted in significant decreases in the kcat/Km values of the enzyme. Because the consensus sequence GXXXXGK(T/S) has been found in many GTP-binding proteins, isoleucine at position 19 in the E. coli adenylosuccinate synthetase was changed to threonine to produce the sequence GDEGKGKT. This mutation, which more closely resembles the consensus sequence, resulted in a 160-fold increase in the Km value for substrate GTP; however, there were no great changes for the other two substrates, IMP and aspartate. Based on these data, we suggest that the N-terminal glycinerich sequence in E. coli adenylosuccinate synthetase plays a more important role in enzyme catalysis than in substrate binding. In addition, a hydrophobic amino acid residue such as isoleucine, leucine, or valine, rather than threonine, may play a critical role in GTP binding in adenosuccinate synthetase. These findings suggest that the glycine-rich sequence in adenylosuccinate synthetase functions differently relative to those in other GTP binding proteins or enzymes.

Adenylosuccinate Synthase↗

PubMed1992

Circulating immunoreactive inhibin and testosterone levels in men with critical illness.

OBJECTIVE: We aimed to concurrently characterize serial changes in circulating immunoreactive inhibin (irINH) and testosterone (T) as reflections of Sertoli and Leydig cell responses to acute critical illness in man. DESIGN: Blood samples were drawn within 24 hours of admission to an Intensive Care Unit and at weekly intervals thereafter for up to 4 weeks while the patient remained in Intensive Care Unit or after discharge to a general ward. PATIENTS: We studied 13 male subjects with critical illness requiring intensive therapy. MEASUREMENTS: Plasma levels of irINH, T, LH, FSH and sex hormone binding globulin (SHBG) were analysed in relation to (i) the severity of illness as indicated by a sepsis score, acute physiology and chronic health evaluation score, and reverse triiodothyronine (rT3) levels and (ii) the outcome of illness as determined by discharge from Intensive Care Unit and the two-month mortality. RESULTS: Overall irINH levels remained normal and correlated negatively with rT3 (r = -0.63, P = 0.001) but not with sepsis, acute physiology and chronic health evaluation score, or gonadotrophin levels. Neither admission nor serial irINH levels significantly distinguished between the different clinical outcomes. In contrast, T levels were depressed and inversely correlated with both sepsis and acute physiology and chronic health evaluation scores (P less than 0.02), and positively with gonadotrophins (P less than 0.01), but not rT3 levels. Men eventually discharged from the Intensive Care Unit showed a rise, while those remaining showed a fall, in T levels (P = 0.02, time-course interaction). Similarly, T levels were lower in patients who died than in survivors, despite the comparable T levels on admission (P = 0.02, time-course interaction). Despite the fall in T levels, gonadotrophin levels remained inappropriately in the eugonadal range but higher in men who were discharged from Intensive Care Unit (P = 0.02, time-course interaction). FSH but not LH levels were correlated with sepsis score (P = 0.02) but not acute physiology and chronic health evaluation score or rT3. CONCLUSIONS: Sertoli cell function as judged by circulating irINH levels is much less affected by acute critical illness than is Leydig cell function as judged by circulating T levels. The suppressive effect of acute critical illness on Leydig cell function is consistent with a hypothalamic-pituitary lesion.

Acute Disease↗

PubMed1992

DNA binding specificity and sequence of Xanthomonas campestris catabolite gene activator protein-like protein.

The Xanthomonas campestris catabolite gene activator protein-like protein (CLP) can substitute for the Escherichia coli catabolite gene activator protein (CAP) in transcription activation at the lac promoter (V. de Crecy-Lagard, P. Glaser, P. Lejeune, O. Sismeiro, C. Barber, M. Daniels, and A. Danchin, J. Bacteriol. 172:5877-5883, 1990). We show that CLP has the same DNA binding specificity as CAP at positions 5, 6, and 7 of the DNA half site. In addition, we show that the amino acids at positions 1 and 2 of the recognition helix of CLP are identical to the amino acids at positions 1 and 2 of the recognition helix of CAP:i.e., Arg at position 1 and Glu at position 2.

Amino Acid Sequence↗

PubMed1992

Cloning and sequencing of IS1086, an Alcaligenes eutrophus insertion element related to IS30 and IS4351.

A new insertion sequence (IS), designated IS1086, was isolated from Alcaligenes eutrophus CH34 by being trapped in plasmid pJV240, which contains the Bacillus subtilis sacB and sacR genes. The 1,106-bp IS1086 element contains partially matched (22 of 28 bp) terminal-inverted repeats and a long open reading frame. Hybridization data suggest the presence of one copy of IS1086 in the strain CH34 heavy-metal resistance plasmid pMOL28 and at least two copies in its chromosome. Analysis of the IS1086 nucleotide sequence revealed striking homology with two other IS elements, IS30 and IS4351, suggesting that they are three close members in a family of phylogenetically related insertion sequences. One open reading frame of the Spiroplasma citri phage SpV1-R8A2 B was also found to be related to this IS family but to a lesser extent. Comparison of the G+C contents of IS30 and IS1086 revealed that they conform to their respective hosts (46 versus 50% for IS30 and Escherichia coli and 64.5% for IS1086 and A. eutrophus). The pressure on the AT/GC ratio led to a very different codon usage in these two closely related IS elements. Results suggesting that IS1086 transposition might be activated by some forms of stress are discussed.

Alcaligenes↗

PubMed1992

Antibodies in the serum of patients with autoimmune thyroid disorders react with a recombinant 98 amino acid fragment of a full length 64 kDa eye muscle membrane protein which is also expressed in the thyroid.

We have tested sera from patients with autoimmune thyroid disorders with or without ophthalmopathy for immunoreactivity, in a dot blot assay, against a recombinant 98 amino acid fragment of a cloned 64 kDa protein, D1, which is expressed in human eye muscle and thyroid, in the form of a Lac Z fusion protein. Tests were positive in 19 out of 40 patients with established thyroid-associated ophthalmopathy (TAO), in 12 out of 21 patients with Graves' hyperthyroidism (GH) without clinically evident ophthalmopathy, in 5 out of 10 patients with thyroid autoimmunity and lid retraction but no other signs of ophthalmopathy, in 4 out of 23 patients with Hashimoto's thyroiditis (HT) without evident ophthalmopathy and in 2 out of 18 patients with benign adenoma or multinodular goitre, but in only 2 out of 37 normal subjects tested. SDS-polyacrylamide gel electrophoresis and Western blotting for an antibody reactive with a 64 kDa antigen in pig eye muscle membranes was also carried out on sera from patients with TAO and GH. While immunoblotting for antibodies reactive with a 64 kDa protein was more often positive in patients with TAO, in whom 58% had serum antibodies which reacted with a 64 kDa protein, this was not the case in patients with GH without eye signs in whom the prevalence of positive immunoblot tests was 35%. Overall there was a fairly close correlation between the two tests although there were many exceptions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

[Effects of aluminum, fluorine and their mixtures on the enzyme activities of jejunal mucus membrane in the perfusion of small intestine of rats in vivo].

Buffer (control), F as NaF (100 mmol/L), Al as AlCl3 (32 and 170 mmol/L) and the two mixtures of Al and F (Al:F = 0.3:0.7 and 0.7:0.3) in Tris-buffered media of pH 7.0 were respectively perfused through the small intestine of rats over a period of 40 min. The jejunum was taken out from each animal immediately. Some of its parts were for HE staining; and the others for enzyme histochemical staining. Fifteen enzymes were observed. The results showed that (1) Fluorine chiefly inhibited the metal-enzymes and metal-activated enzymes; aluminum mainly depressed the activities of enzymes in relation to the cell energy metabolism, such as hydrogenases and oxidase. (2) The decreased activities of enzymes induced by Al or F increased significantly after mixing with each other, indicating that the simultaneous existence of Al and F decreased their ionic concentrations, so that strong antagonistic effects on the inhibition of enzymes were noticed since F or Al inhibited enzyme activities by their ions. (3) A high dose of Al intensively inhibited the enzymes related to the cell energy metabolism, which explained why less quantity of Al was absorbed in animals with high dose of Al than that of low dose Al seen in the absorption experiment. (4) The enzyme activities in the animals given high dose of Al mixed with F apparently were elevated in comparison with that in the animals given a pure high dose of Al which was the result of antagonistic effects of F on the inhibition of enzyme activities by Al, therefore the quantity of the absorbed Al was high.

Aluminum↗

PubMed1992

[The relation between acupuncture manipulations and responsive discharges of cutaneous receptors].

Nine types of mechanoreceptors of hair skin in 46 rabbits were identified by recording discharges of single afferent fiber in posterior femoral cutaneous nerve from fine filaments by dissection. When seven manipulations, i.e. lift and thrust, twist and twirl, rotate, serape, flike the needle and finger-pressure were used to stimulate each receptor, their responsive discharges were observed. Data at 165 units were collected totally, 89 units in which were for the relation between manipulations and discharge patterns, and the other 76 units for discharges responding to manipulations at different distances from the receptive field. Nine types of receptors having been observed are able to respond to any acupuncture manipulations, it is thus clear that there is not any special "acupuncture receptor." Same kind of discharge pattern existed in different types of receptor when stimulated by the same acupuncture manipulation, whereas different discharge patterns can be found at the same unit when the manipulation changes. We believe that it is due to the movement form; force amount and time duration of the manipulations. Receptors responding to acupuncture were not limited to one point only, but involving a certain field surrounding the needle point. The size of this field varied with the types of receptors and kinds of manipulations. Our previous articles had reported that the acupuncture photograph leading from nerve and building on impulses induced by acupuncture and the groups of afferent fibers conducting acupuncture signals changed with different manipulations, in this paper the reasons for that have been expounded by presenting the relationship between the responsive discharges of receptors and the manipulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Acupuncture Therapy↗

PubMed1992

[Aluminum and fluorine in blood and bone of rats fed on diet mixed with various contents of aluminum, fluoride or their mixture].

Wistar rats were divided into 8 groups:control, 300 ppm F, 130 ppm F, 300 ppm Al, 1200 ppm Al, 130 ppm Al + 130 ppm F. 300 ppm Al + 300 ppm F and 1200 ppm Al + 300 ppm F. The chemicals were mixed into the standard diet. The animals were fed on the diets for 12 weeks. Contents of F, Al, Ca and P in the blood (or serum) and humerus were determined at the end of 12 weeks. The results showed that the level of F in the blood and bone in the unadulterated F group was increased, especially F in the bone reached a level more than 10 times that of the control. In the 3 mixture groups, blood F and bone F were lowered, while blood F was restored to normal level, but bone F was not nevertheless, the results showed that Al was in antagonism to the absorption of F. In the unadulterated Al groups, blood and bone Al did not parallel with the amount of Al administered. The level of Al in the median Al group was higher than that of the high Al group. Taking the level of blood and bone Al as a measure, when different doses of Al were administered with F, in the low and median dosage of Al, F was in antagonism to Al absorption, but in case of high dosage of Al, F was in potentiation to Al absorption. In all the experimental groups serum P was elevated, but serum Ca was not disturbed. Bone Ca and P were decreased only in the 3 groups with unadulterated F as well as unadulterated and adulterated high dosage of Al. Mechanism of the nonlinearity of Al absorption vs Al dosage, as well as the dual effect of F on the absorption of Al was proposed.

Aluminum↗

PubMed1991

Evidence for an arginine residue at the substrate binding site of Escherichia coli adenylosuccinate synthetase as studied by chemical modification and site-directed mutagenesis.

Chemical modification of adenylosuccinate synthetase from Escherichia coli with phenylglyoxal resulted in an inhibition of enzyme activity with a second-order rate constant of 13.6 M-1 min-1. The substrates, GTP or IMP, partially protected the enzyme against inactivation by the chemical modification. The other substrate, aspartate, had no such effect even at a high concentration. In the presence of both IMP and GTP during the modification, nearly complete protection of the enzyme against inactivation was observed. Stoichiometry studies with [7-14C]phenylglyoxal showed that only 1 reactive arginine residue was modified by the chemical reagent and that this arginine residue could be shielded by GTP and IMP. Sequence analysis of tryptic peptides indicated that Arg147 is the site of phenylglyoxal chemical modification. This arginine has been changed to leucine by site-directed mutagenesis. The mutant enzyme (R147L) showed increased Michaelis constants for IMP and GTP relative to the wild-type system, whereas the Km for aspartate exhibited a modest decrease as compared with the native enzyme. In addition, kcat of the R147L mutant decreased by a factor of 1.3 x 10(4). On the bases of these observations, it is suggested that Arg147 is critical for enzyme catalysis.

Adenylosuccinate Synthase↗

PubMed1991

Expression of human brain hexokinase in Escherichia coli: purification and characterization of the expressed enzyme.

Human brain hexokinase (hexokinase I) was produced in Escherichia coli from a synthetic gene under control of the bacteriophage T7 promoter. The expressed coding region derives from a human cDNA clone thought to specify hexokinase I based on amino acid sequence identity between the predicted translation product and hexokinase I from rat brain. The open reading frame from this cDNA was fused to the promoter and 5' flanking region of T7 gene 10, and expressed in E. coli by induction of T7 RNA polymerase. Induced cells contained a hexokinase activity and an abundant protein of apparent molecular weight 100,000, neither of which was present in cells lacking T7 RNA polymerase. Enzyme purified to near homogeneity consisted of a 100,000 Da protein, the size predicted from the nucleotide sequence of the expressed cDNA. The purified enzyme had Michaelis constants of 32 microM and 0.3 mM for glucose and ATP, respectively, and bound to rat liver mitochondria in the presence of MgCl2. Enzymatic activity was inhibited by glucose-6-P and this inhibition was relieved by inorganic phosphate. Deinhibition by phosphate is a property specific to brain hexokinase.

Base Sequence↗

PubMed1991

Effects of streptozotocin/bis-chloroethylnitrosourea combination therapy on O6-methylguanine DNA methyltransferase activity and mRNA levels in HT-29 cells in vitro.

Treatment of chloroethylnitrosourea-resistant cells with streptozotocin (STZ) prior to bis-chloroethylnitrosourea (BCNU) exposure has been shown to result in a depletion of O6-methylguanine DNA methyltransferase (MGMT) activity, increased BCNU-induced interstrand cross-linking, and a 2-3 log enhancement of BCNU cytotoxicity in vitro. The current study was undertaken to define the kinetics of repletion of MGMT activity following the STZ/BCNU combination and to assess at the molecular level the effects of the combination on MGMT mRNA expression. Results demonstrate that MGMT activity can be depleted by greater than 90% relative to untreated controls using an optimized STZ/BCNU combination regimen and that greater than 50% depletion can be maintained for at least 24 h. This depletion appears to be independent of effects at the mRNA level because neither STZ alone nor the STZ/BCNU combination significantly altered steady state levels of MGMT mRNA. Cytotoxicity studies are consistent with MGMT repletion data and demonstrate that, as the interval between STZ and BCNU exposures increases, the degree of enhanced cytotoxicity induced by the combination relative to BCNU alone decreases. These results suggest that the enhanced cytotoxicity induced by the STZ/BCNU combination over BCNU treatment alone is favored by both the lack of induction of expression of MGMT mRNA and by slow reappearance of MGMT activity.

Carmustine↗

PubMed1991

Cloning and sequencing of a novel 64-kDa autoantigen recognized by patients with autoimmune thyroid disease.

Screening 10(6) plaque-forming units from a lambda gt11 human thyroid cDNA library with a pool of 10 sera from patients with Hashimoto's thyroiditis resulted in the isolation of a clone, D1, of 292 basepairs with an open reading frame of 97 amino acids which did not share significant similarity with any known protein. Rescreening the library using D1 as a probe led to the full-length cDNA being cloned and sequenced which has the potential to encode a 572-amino acid polypeptide. This would correspond to a 63-kDa nonglycosylated protein which is probably membrane bound. The recombinant fusion protein from the original D1 clone was recognized in dot blot or Western blot assays by 4 of 19 patients with Hashimoto's thyroiditis, 3 of 9 patients with Graves' disease, and 1 of 6 patients with idiopathic myxedema; all other sera (12), including that from normal subjects, were negative. Clone affinity-purified autoantibodies bound to a protein of 64 kDa in a Western blot of human thyroid tissue. Using D1 as a probe in a Northern blot revealed 3.9-kilobase (kb) transcripts in poly(A)+ RNA from normal human thyroid and extraocular muscle, but not skeletal muscle. The dog equivalent of D1 cDNA was isolated by screening 10(6) plaque-forming units from a dog thyroid cDNA library using clone D1. A fragment of dog cDNA was, in turn, used as a probe in a Northern blot of dog poly(A)+ RNAs from thyroid, brain, lung, heart, liver, kidney, spleen, and stomach; a faint signal at 3.9 kb was observed in all tissues except the thyroid, which displayed a strong transcript of 2.6 kb. It is concluded that the D1 cDNA clone encodes an autoantigen shared by the thyroid and eye muscle. Its possible relevance to autoimmune ophthalmopathy is discussed.

Animals↗

PubMed1991

Pulsatile LH secretion in streptozotocin-induced diabetes in the rat.

This study aimed to determine the effect of streptozotocin (STZ)-induced diabetes on pulsatile LH secretion in the mature male rat. LH pulse frequency was reduced by 56% and pulse amplitude by 54%, with a consequential decrease of 72% in mean LH levels 8 days after i.v. administration of STZ (55 mg/kg) to castrated Wistar rats compared with castrated non-diabetic controls. Twice daily insulin treatment completely reversed all parameters of pulsatile LH secretion to control values. Food-restricted non-diabetic controls, studied to distinguish the metabolic effect of diabetes from that of concurrent weight loss, demonstrated a 34% reduction in LH pulse frequency but no significant changes in LH pulse amplitude or mean LH levels compared with non-diabetic controls given free access to food. To distinguish whether the decreased LH pulse amplitude in diabetes was due to a reduction in either the quantity of hypothalamic gonadotrophin-releasing hormone (GnRH) released per secretory episode or to decreased pituitary responsiveness to GnRH, the responsiveness of the pituitary to exogenous GnRH (1-1000 ng/kg body weight) was tested in diabetic rats after castration, using a full Latin square experimental design. The net LH response (total area under response curve over 40 min following GnRH) was decreased by 33% (P = 0.001) in diabetic compared with control rats. The decreased LH pulse frequency in STZ-induced diabetes therefore suggests that the metabolic effect of diabetes is to decelerate directly the firing rate of the hypothalamic GnRH pulse generator independent of testicular feedback. These effects were fully reversed by insulin treatment and were only partly due to the associated weight loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

[Aluminum and fluorine absorption in a perfusion system of rat small intestine in vivo].

Mixtures of aluminum an fluorine in two different ratios in tris-hydroxy-methyl-aminomethane buffered media of pH 7.0 were perfused respectively through the small intestine of the in vivo rat over a period of 40 min. The contents of aluminum and fluorine in the portal vein blood obtained from different perfusion periods were detected and determined simultaneously. The results showed that fluorine absorption was not significant in the mixtures. An obviously large amount of aluminum was absorbed in the mixture with a higher proportion of aluminum (4660 micrograms/ml Al + 200 micrograms/ml F/L), while in the mixture with a lower dose of aluminum (860 micrograms/ml Al + 200 micrograms F/L), a small quantity of aluminum was absorbed. It is evident that the mechanism by which aluminum inhibits fluorine toxicity is that aluminum decreases the intestinal fluorine absorption by the formation of aluminum fluoride complex.

Aluminum↗

PubMed1991

Importance of viability and attachment to an ascites tumor in the release of plasminogen activator.

Tumor plasminogen activator (PA) has been alleged to play a role in the growth and metastasis of tumors. Before such a role can be realized, PA first must be released from tumor cells. Having determined intra- and extracellular PA and PA-inhibitor activities in an experimental pancreatic ascites tumor grown in hamsters, the release of PA from these cells was investigated. No PA activity was detected in the suspension medium of freshly isolated tumor cells; inclusion of plasminogen, fibrinogen, or collagen in the medium yielded similar negative results. On the other hand, PA activity was demonstrated to be released in a time-dependent manner from these tumor cells embedded in fibrin clots. Plasminogen activator activity also was not found in the suspension medium of frozen-thawed tumor cells, despite the fact that most of them had breaks on their cell membrane. Unlike freshly isolated tumor cells, PA was not released from frozen-thawed cells embedded in fibrin clots. Full PA activity was demonstrated in frozen-thawed cells treated with Triton X-100, however. Frozen-thawed cells exhibited signs of severe damage, and more than 80% of them failed to exclude trypan blue. Obviously PA is released from viable tumor cells embedded in fibrin clots but not suspended in artificial medium. The PA-release mechanism, not PA itself, is destroyed in cells rendered nonviable by freeze thawing.

Animals↗

PubMed1990

Chemical modification of adenylosuccinate synthetase from Escherichia coli by pyridoxal 5'-phosphate. Identification of an active site lysyl residue.

Incubation of adenylosuccinate synthetase from Escherichia coli with low concentrations of pyridoxal 5'-phosphate (PLP) resulted in a rapid loss of activity (92%), concomitant with the formation of a Schiff base. The inactivation of the enzyme by PLP is apparently first order with respect to PLP. The pseudo-first order rate constant, Kapp, showed a hyperbolic dependence on the concentration of PLP, indicating that a kinetically significant PLP.enzyme intermediate is formed during the inactivation process. Stoichiometry and peptide isolation studies showed that 2 lysine residues were modified during reaction of the enzyme with PLP. The three substrates of adenylosuccinate synthetase (GTP, IMP, and aspartate) showed different effects in their ability to protect the enzyme against PLP inactivation. Complete protection of the enzyme against inactivation can be observed only in the presence of high concentrations of GTP. One lysine residue was protected under these conditions. In contrast to GTP, addition of the other two substrates either alone or together to reaction mixtures did not render protection. Peptide mapping by digesting the enzyme with trypsin revealed that the lysine shielded by GTP is Lys140. Replacing the Lys140 with Ile140 by site-directed mutagenesis resulted in total loss of the activity. These results suggest that Lys140 may play an important role in enzymatic activity.

Adenylosuccinate Synthase↗