Characterization of the swine adipocyte A1 adenosine receptor using an optimized assay system

The radioligand binding assay of A1 adenosine receptors in adipocyte crude plasma membrane from Yucatan miniature swine was optimized by evaluating 17 factors involved in the assay. Significant effects of CHAPS, adenosine deaminase, EDTA, pre-rinsing glass fiber filters and pH were found for the binding measurements. Using the optimized procedure, [3H]8-cyclopentyl-1,3-dipropylxanthine, ([3H]-DPCPX) binding to A1 adenosine receptors in swine subcutaneous adipocyte crude plasma membrane was measured; Bmax and Kd values were 479 +/- 77 fmol/mg protein and 0.87 +/- 0.10 nM, respectively. Values for mesenteric adipose tissue from sedentary swine and subcutaneous adipose tissue from exercise-trained swine were also measured.

Fears in Chinese children and adolescents and their relations to anxiety and depression

In the present study, we examined the pattern and intensity of fear in 825 Chinese children and adolescents. Although many of the fears paralleled those reported in Western samples (Australia, England and the United States), some differences were noted. In particular, Chinese children and adolescents reported heightened levels of social-evaluative fears. This pattern was especially evident for children between 11 and 13 years of age. A developmental-cultural hypothesis was put forth to account for these findings. In addition, modest relations were found between our measure of fear and measures of anxiety and depression. Results were explored in terms of the uniqueness of the constructs of fear, anxiety and depression and their contributions to a more global construct of negative distress, labeled 'negative affectivity'.

Identification of amino acid-base contacts in the Myc-DNA complex by site-specific bromouracil mediated photocrosslinking

Myc binds to a 6 bp 2-fold symmetric DNA site: 5'-C-3A-2C-1G+1T+2G+3-3'. Using site-specific 5-bromouracil mediated photocrosslinking, we show that His336 of Myc contacts, or is close to, the thymine 5-methyl group at 2-fold symmetry-related positions -2 and +2 of the DNA site in the Myc-DNA complex. Our results strongly suggest that homologous amino acids of Myc and Max make equivalent contacts in the respective protein-DNA complexes.

Design of antineoplastic agents on the basis of the "2-phenylnaphthalene-type" structural pattern. 2. Synthesis and biological activity studies of benzo]b]naphtho[2,3-d]furan-6,11-dione derivatives

Based on the "2-phenylnaphthalene-type" structural pattern hypothesis developed in our laboratory, a number of benzo[b]naphtho[2,3-d]furan-6,11-diones were designed, synthesized, and evaluated in vitro for their inhibitory action against the growth of human promyelocytic leukemia cells (HL-60), small-cell lung cancer (SCLC), SCLC cells resistant to cisplatin (SCLC/CDDP), National Cancer Institute's disease-oriented primary antitumor 60 cell-line panel, and drug-stimulated topoisomerase II-mediated DNA cleavages. Many compounds designed were found to possess potent activity in one or more of the biological tests. In general, activity found in one of the cell lines tested is often echoed in other cell lines and many also expressed substantial inhibitory activity against topoisomerase II-mediated cleavage activities. One of these compounds, 3-[2-(dimethylamino)ethoxy]-1-hydroxybenzo[b]naphthol[2,3-d]furan- 6,11-dione (8j), exhibited strong inhibitory activity throughout the entire series of test panel. Thus, it appears that the proposed structural pattern hypothesis has received substantial support through experimental verification.

[Combined operation for the foreign body in the eye complicated with traumatic cataract: an analysis of 88 cases]

The foreign body in the eye complicated with traumatic cataract is one of the common causes of blindness. The rate of blindness ranges from 20% to 48.9%. This paper analyses combined operation for 88 cases of foreign body in the eye with traumatic cataract. The visual acuity below 0.05 accounted for 85.2% of the cases before operation and reduced to 27.3% after operation. Postoperatively, the corrected visual acuities were from 0.06 to 1.5 in 73.3% of the cases and 0.6 to 1.5 in 22.7% respectively. The patients should be treated with combined operation earlier. The way of operation depends on the property and the location of foreign body and the situation of lens. Chinese-Western medicine treatment should be used postoperatively to control the tissue response. Combined operation can improve the effect, reduce the complication, the number of operation and decrease medical expenses.

Mutational studies of human DNA polymerase alpha. Serine 867 in the second most conserved region among alpha-like DNA polymerases is involved in primer binding and mispair primer extension

The second most conserved region of alpha-like DNA polymerases, region II, spans a block of 40 amino acid residues centered at the core sequence -DFNSLYPSII-. In the previous paper, we described mutational studies of 3 amino acid residues in region II which includes 2 amino acid residues in the core sequence. We showed that residues Asp860 and Tyr865 in the core sequence are involved in substrate deoxynucleotide triphosphate (dNTP) binding. We further showed that the phenyl moiety of the Tyr865 side chain interacts with the incoming dNTP and is responsible for the misinsertion fidelity of the enzyme. In this report, we investigated the function of 2 serine residues, Ser863 and Ser867, in this core sequence. Mutation of these 2 Ser residues to either Ala or Thr yielded mutant enzymes with similar Km for dNTPs, kcat, processivity, and misinsertion fidelity of DNA synthesis as the wild type enzyme. However, mutation of Ser867 to Ala demonstrated a 30-fold increase in Km for primer-template and a 5-fold higher KD for binding primer-template. DNA footprinting experiments of primer with the dideoxynucleotide terminus indicated that the structural feature of the primer recognized by Ser867 is the 3'-OH terminus. Single-stranded DNA inhibition data suggest that removal of the hydroxyl side chain of Ser867 affects the polymerase's interaction with primer and not with template. Mutation of Ser867 to Ala also decreases the mutant enzyme's Km for dNTP to extend a mispaired primer and thus enhances its capacity to extend a mispaired primer terminus. These data support the conclusion that the hydroxyl side chain of Ser867 of human DNA polymerase alpha is involved in primer interaction during DNA synthesis and plays an essential role in mispair extension fidelity of DNA synthesis.

Mutational studies of human DNA polymerase alpha. Identification of residues critical for deoxynucleotide binding and misinsertion fidelity of DNA synthesis

Conserved site-directed mutations were introduced into the second most conserved amino acid region, region II, of the human DNA polymerase alpha catalytic subunit. These mutants were expressed in the baculovirus system and purified to near homogeneity. The mutants had polymerase activity ranging from 4 to 60% compared with the wild type polymerase alpha. Steady-state kinetic analysis of mutants G841A, D860A, D860S, D860N, Y865S, and Y865F demonstrated no significant difference in their Km values for primer-template compared with that of the wild type enzyme. In contrast, mutants D860A, Y865S, and Y865F showed a 5-10-fold increase in the Km for deoxynucleotide triphosphate (dNTP) compared with the wild type enzyme. DNA synthetic fidelity studies of these mutants showed that mutant Y865S but not Y865F had a greater than 10-fold higher misinsertion efficiency than the wild type enzyme in Mg(2+)-catalyzed reactions. However, with Mn2+ as the metal activator, Y865S and Y865F demonstrated a 2- and 9-fold higher misinsertion efficiency, respectively. These results indicate that Asp860 and Tyr865 in region II of human DNA polymerase alpha are involved in incoming dNTP substrate binding. Using three deoxynucleotide structural analogs as probes, we show that the nucleotide base is the structural requirement for dNTP binding with Tyr865. Furthermore, abolishing the hydrophobic phenyl ring side chain of Tyr865 by replacing tyrosine with serine rendered the enzyme resistant to aphidicolin. Results of these studies strongly suggest that the phenyl ring of Tyr865 directly interacts with the nucleotide base moiety of the dNTP and plays a critical role in the misinsertion fidelity of DNA synthesis. Although mutation of Gly841 to Ala did not affect the binding of primer-template, it had a significant decrease in kcat, an increase in Km for dNTP, a striking decrease of processivity, and also resistance to aphidicolin. Thus, mutation of this residue, Gly841, which is highly conserved among the alpha-like DNA polymerases, appears to affect both catalysis and substrate deoxynucleotide binding. This suggests that Gly841 is essential for the maintenance of the overall structure of the polymerase alpha catalytic site.

LH pulsatility, biopotency, and clearance during undernutrition in orchidectomized mature rats

The effect of food restriction on circulating luteinizing hormone (LH) levels in orchidectomized rats is controversial. The present study demonstrates that decreasing food intake by 50% for 3-10 days in orchidectomized rats increases LH pulse amplitude, length, area under pulse curve, and mean levels but decreases LH pulse frequency compared with ad-lib fed, orchidectomized controls. The effects on pulsatile LH secretion of food reduction by 50% with or without dilution by cellulose to maintain food volume in orchidectomized rats were also examined. Food volume influences pulsatile LH secretion independent of macronutrient effect after 3 days of food restriction, but subsequently macronutrient deprivation predominates. The exaggerated increase in LH levels in orchidectomized rats subject to food restriction for 7 days was not due to immunochemical or chromatographic heterogeneity or alteration in biopotency of circulating LH molecules. Intravenously injected 125I-labeled rat LH analyzed by noncompartmental modeling revealed that neither LH clearance nor mean residence time was reduced by food restriction. We conclude that during food restriction in orchidectomized rats, increases in LH pulse amplitude exceed and precede the decreases in LH pulse frequency, although the early changes in pulse amplitude are predominantly due to reduced food volume rather than macronutrient deprivation.

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.

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.

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.

[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.

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).

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.

[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.

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.

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)

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)

Effects of ethane dimethane sulphonate and orchidectomy on luteinizing hormone secretion

Abstract The aim of this study was to determine whether testicular products of non-Leydig cell origin modulate rat luteinizing hormone (LH) secretion in vivo. We therefore compared the effects of ethane dimethane sulphonate (EDS), a toxin regarded as highly selective for Leydig cells, with that of bilateral orchidectomy on LH secretion in mature male Wistar rats. The intention was thereby to compare the effects of selective removal of Leydig cells with that of removing both Leydig cells and seminiferous tubules, respectively. Following a single dose of EDS (75 mg/kg, ip), plasma LH concentrations rose equally with those of castrated rats for the first 3 days. After that time, however, plasma LH concentrations in the EDS-treated rats fell progressively below those of the orchidectomized rats despite the continuing castrate level of circulating testosterone until Day 17. The effects of EDS treatment or orchidectomy on pulsatile LH secretion were then compared after 11 days to castrate levels of testosterone. EDS-treated rats demonstrated reduced LH pulse amplitude, mean plasma LH levels and net LH secretion compared with castrate rats, although LH pulse frequency was unaltered. However, a further group of rats treated with EDS and orchidectomized failed to demonstrate that these changes were fully reversed by the castration and therefore EDS may have direct effects upon pituitary LH secretion. In order to determine the mechanism of the reduced LH pulse amplitude after EDS treatment, a further study was conducted to determine whether EDS treatment resulted in reduced pituitary sensitivity to gonadotropin-releasing hormone (GnRH). Responsiveness of pituitary LH to exogenous GnRH (0.01 to 10 mug/kg body wt) was studied 11 days after removal of testicular testosterone feedback by either EDS or castration. Plasma LH response was linearly related to the log of the GnRH dose. At 10 min after GnRH administration, the plasma LH response in EDS-treated rats was less sensitive than in castrate rats. We conclude that the lesser augmentation of LH secretion between Days 3 and 17 after EDS treatment compared with castrate rats cannot be explained solely by changes in Leydig cell secretion but may involve direct effects of EDS on pituitary LH secretion or non-Leydig cell testicular products. Dampening of LH pulse amplitude without change in LH pulse frequency together with the reduced sensitivity to GnRH in EDS-treated rats suggests that this toxin may have direct effects on pituitary LH secretion independent of its effects on Leydig cell function.

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.

[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.

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.

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.

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.

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.

[An acute experimental study on the combinations of aluminum and fluorine in various ratios]

The joint actions were assessed by four methods after male Wistar rats had been acutely intoxicated with nine proportional mixtures of Al and F. Strong antagonistic effects of Al on F were observed in the mixtures, in which the ratio of Al to F ranged from 0.8:0.2 to 0.1:0.9. The optimum ratio of Al to F for antagonism ranged from 0.3:0.7 to 0.1:0.9 without periorbital bleeding that was a regular finding in Al acute toxicity on the rat to be seen. When the amount of Al in the mixture was below 5% or above 90%, no antagonistic effect was shown. The kinetics on the absorption under the condition of Al and F existing simultaneously is still unknown, and warrants further investigation.

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.

Identification of different classes of nonessential sulfhydryl groups in Escherichia coli adenylosuccinate synthetase

Reaction of Escherichia coli adenylosuccinate synthetase with the thiol reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) or N-ethylmaleimide (NEM) leads to modification of one cysteine residue per enzyme monomer without significant loss of enzyme activity. Modification of a second cysteine residue occurs under mild denaturing conditions (3.5 M urea), and derivatization of this thiol followed by dialysis results in complete loss of enzyme activity. The remaining two cysteine residues react with DTNB only after treatment with 8 M urea. The location of the various cysteine residues in the enzyme was established by using [14C]NEM followed by tryptic digestion and radiopeptide isolation. The reactive cysteine has been identified as Cys291, and the thiol exposed with 3.5 M urea is Cys344. When Cys344 was replaced by either serine or alanine, the mutant enzymes were found to be as active as the wild-type enzyme. These findings point to the nonessential role of Cys344 in adenylosuccinate synthetase.

Comparison of O-6-methylguanine DNA methyltransferase (MGMT) mRNA levels in Mer+ and Mer- human tumor cell lines containing the MGMT gene by the polymerase chain reaction technique

O-6-Alkylguanine is a mutagenic and carcinogenic DNA lesion induced by a variety of alkylating agents, including the chloroethylnitrosoureas. The lesion is repaired by the alkyl-accepting suicide enzyme O-6-methylguanine DNA methyltransferase (MGMT). Approximately 25% of cell lines derived from human tumors are phenotypically deficient in this enzyme and are described as Mer-. Recent cloning of the human MGMT cDNA (Tano, K.; Shiota, S.; Collier, J.; Foote, R.S.; Mitra, S. Proc. Natl. Acad. Sci. USA 87:686-690; 1990) has allowed for a more detailed analysis of the basis of the Mer- phenotype in human Mer- tumor cell lines. Using the polymerase chain reaction (PCR) technique, an MGMT cDNA probe based on the published sequence was generated. The probe and the PCR technique were then used to analyze the presence and expression of the MGMT gene in two Mer+ and four Mer- lines, including one SV40-transformed Mer- line and three Mer- human tumor cell lines. The data demonstrate that while all six cell lines contained a relatively nonamplified, nonrearranged MGMT gene, Mer- lines contained levels of MGMT mRNA detectable only by PCR analysis. Of the three Mer- tumor cell lines examined, two (COLO 320 HSR, A1235) contained MGMT mRNA levels that were four to five orders of magnitude lower than that of the prototype Mer+ tumor line (HT-29), while one (BE) contained no consistently detectable MGMT mRNA. These results suggest that in the human Mer- tumor lines tested, the Mer- phenotype was mediated by a severe reduction in MGMT mRNA levels, despite the presence of the MGMT gene.

Pulsatile luteinizing hormone secretion in the rat: methodological aspects of cannulation route and sampling intensity

Abstract We have investigated some requirements for valid estimates of pulsatile luteinizing hormone (LH) secretion in the castrate male rat. The choice of cannulation route and the minimal sampling intensity required to produce stable, unbiased estimates of parameters of pulsatile LH secretion were examined. Castrate mature male Wistar rats with unilateral ligation of a carotid artery (an inevitable consequence of carotid artery cannulation) had a 47% reduction in mean LH levels (1.8 vs 3.4 ng/ml, P< 0.011) attributable to a 40% reduction in LH pulse frequency (6.2 vs 10.4 peaks/6 h P<0.006) without change in LH pulse amplitude or other parameters of pulsatile LH secretion. In another study, a range of sampling intensities were examined to derive estimates of pulsatile LH secretion. Parameter estimates derived from the most intensive regime (q10 min sampling for 6 h) were compared with estimates of pulsatile LH secretion parameters determined from less intensive derivative sub-series composed of either fixed sampling frequency, but variable total study duration (i.e. the first 1, 2, 3, 4 and 5 h at 10 min intervals), or a fixed total study duration but variable sampling frequency. LH pulse frequency (or its inverse, interpulse interval) was quite sensitive to sampling intensity whereas pulse amplitude, maximum, minimum and overall mean LH were estimated accurately at even relatively low sampling intensity (q20 min for one h duration). Lower frequency sampling (q20 min) gave marked underestimates of LH pulse frequency (4.9 vs 10.4 peaks/6 h, P<0.05) compared with q10min sampling over a 6h study. These results indicated that for stable and unbiased estimates of pulsatile LH secretion in the castrate mature male rat it is necessary (but may not be sufficient) to (1) avoid carotid artery cannulation and (2) undertake blood sampling at intervals of not more than 10 min for at least 3 h.

Towards an antigenic map of human thyroglobulin: identification of ten epitope-bearing sequences within the primary structure of thyroglobulin

The aim of this study was to define, at the molecular level, epitopes of thyroglobulin recognized by heterologous antibodies and autoantisera. One hundred thousand clones from a lambda gt 11 human thyroid cDNA library were screened using a rabbit antibody to human thyroglobulin at a 1:2000 dilution. Twenty clones were plaque-purified to homogeneity, and characterization and sequencing of their cDNA inserts showed that they represented four distinct regions of the thyroglobulin molecule, one of them being the 22 carboxyl-terminal amino acids. Rescreening of the library with the same rabbit antibody to human thyroglobulin absorbed with peptides encoded by the carboxyl-terminal clone, led to the definition of six further epitope-bearing fragments of thyroglobulin. The ten regions that we have identified were recognized by ten further rabbit antibodies to human thyroglobulin, showing that they are representative of the repertoire of heterologous epitopes. In contrast, none of the ten heteroepitope-bearing fragments was recognized by sera from ten patients with autoimmune thyroid disease with various titres of thyroglobulin antibodies. Screening of 2 x 10(6) clones from the library using a pool of ten autoantisera (individual sera diluted to 1:1000), and of 1 x 10(6) clones using a single autoantiserum of very high antithyroglobulin titre (diluted 1:400) resulted in no thyroglobulin clones being isolated. The significance of these results to the immune process is discussed.

Definition, at the molecular level, of a thyroglobulin-acetylcholinesterase shared epitope: study of its pathophysiological significance in patients with Graves' ophthalmopathy

The nature of the putative autoantigen in Graves' ophthalmopathy (Go) remains an enigma but the sequence similarity between thyroglobulin (Tg) and acetylcholinesterase (ACHE) provides a rationale for epitopes which are common to the thyroid gland and the eye orbit. In an attempt to define the shared epitope, we have screened a lambda gt 11 human thyroid cDNA library using a polyclonal antibody to Torpedo ACHE and isolated two clones, which upon sequencing, were shown to contain Tg segments, corresponding to portions of the C terminal part of the molecule which has a high similarity with ACHE. Having demonstrated the existence of an epitope common to Tg and ACHE, the clones have been further tested and found to be positive in lysis plaque assays with 1/10 sera from patients with Hashimoto's thyroiditis (HT), 8/8 from patients with Graves' ophthalmopathy and 0/8 normal sera. We have investigated the physiological significance of this common epitope by in situ immunolocalization studies in which the polyclonal antibody to Torpedo ACHE (which was used for screening the library) and immunoglobulins (Igs) from 6 Go patients tested were shown to bind to end plate regions of human foetal muscle fibres which were concurrently shown to be rich in cholinesterase activity: Igs from 3 normal individuals and 2 patients with Hashimoto's thyroiditis did not bind. The results demonstrate and characterize an epitope which is common to Tg and ACHE and show that Go patients Igs contain antibodies which bind to muscle end plates rich in cholinesterase. The significance of these findings to the pathogenesis of Go is discussed.

Susceptibility of irradiated bovine aortic endothelial cells to injury

Using cultured bovine aortic endothelial cells (BAEC), the authors attempted to determine whether prior irradiation would alter the susceptibility of these cells to three known injurious stimuli and, if so, whether the alteration would be related to radiation dose. BAEC were irradiated with 0, 5, or 10 Gy of gamma rays and, on the third postirradiation day, exposed to fibrin, nicotine, or bacterial endotoxin (lipopolysaccharide, LPS). Release of prelabeled 51Cr, representing cell lysis, cell detachment, or a combination of the two, was determined. Significant differences between irradiated and control cells were determined by using paired Student's t-tests. Irradiation did not appear to have altered the sensitivity of BAEC to fibrin-induced injury. Cells irradiated with 10 Gy of gamma rays, but generally not those irradiated with half this dose, showed a heightened susceptibility to nicotine. Contrary to the nicotine results, irradiated cells showed less cell detachment and lysis after exposure to LPS. These results suggest that the susceptibility of irradiated BAEC to harmful stimuli depends largely on the nature of the stimulus as well as the radiation dose.

Cellular and extracellular plasminogen activator and inhibitor in an experimental tumour

We determined plasminogen activator (PA) and PA inhibitor (PAI) activities in the intra- and extracellular compartments of an experimental pancreatic ascites tumour with indirect and direct functional assays, and partially characterized these activities on SDS-polyacrylamide gels coupled with fibrin and reverse fibrin autography. Intact tumour cells caused lysis of plasminogen-rich but not plasminogen-free fibrin clots, and the extent of lysis of the former was related to tumour cell count. Direct assay of PA with a synthetic substrate yielded an equivalent of 109 urokinase units per 10(9) tumour cells. No PAI activity was demonstrated in tumour cells with functional assays. Contrary to tumour cells, cell-free ascitic fluids caused no lysis of fibrin clots. Instead, it inhibited tumour cell- and urokinase-induced, but not plasmin-induced, clot lysis in a dose-dependent fashion. Although functional assays failed to demonstrate PA in ascitic fluid and PAI in tumour cells, both activities were detected in electrophoresed samples of cell lysates and fluids by fibrin and reverse fibrin autography. In tumour cells, a mixture of tissue-type PA (tPA) and urokinase-type PA (uPA) were present. In the fluid, uPA together with two other PAs with greater molecular weights than tPA were detected.

A nonsense mutation causes hereditary goitre in the Afrikander cattle and unmasks alternative splicing of thyroglobulin transcripts

The hereditary goitre of Afrikander cattle is an autosomal recessive disease characterized in homozygotes by the production of abnormal thyroglobulin (Tg) and the coexistence in the thyroid of normal-sized 8.4-kilobase (kb) Tg mRNA with a misspliced 7.3-kb message having lost exon 9. We have cloned and sequenced the cDNA segment corresponding to the abnormal exon 8-exon 10 junction and the relevant genomic DNA region. The mutation responsible for the disease is a cytosine to thymine transition creating a stop codon at position 697 in exon 9. The original reading frame is maintained in the 7.3-kb mRNA, which, as it lacks the mutated exon, is translatable into a potentially functional protein. This puzzling phenotype in which a mutated exon is apparently removed selectively from transcripts by alternative splicing leads us to suggest that the 7.3-kb transcript could be present in normal animals. Using a sensitive oligonucleotide hybridization assay, we have demonstrated that a 7.3-kb mRNA lacking exon 9 does exist in normal thyroids as a minor mRNA species. As it is fully translatable, the 7.3-kb mRNA is expected to be more stable than the normal-sized 8.4-kb message. This probably accounts for the higher proportion of 7.3-kb transcript found in the goitre.