[Measurement of NOS activity by monitoring the conversion of 3H-arginine]

OBJECTIVE

To establish a method for measuring the constitutive and inducible nitric oxide synthase (NOS) through the conversion of L-3H arginine to L-3H citrulline.

METHODS

NOS extracted from cerebellar of porcine and rat was purificated through DEAE cellulose or/and 2', 5', -ADP agarose. NOS activity was assayed by monitoring the conversion of 3H-arginine to 3H-citrulline.

RESULTS

A 4,460 fold purification of the porcine cerebellar NOS was obtained with an activity of 669 pmol mg-1 min-1 and a 2.7% recovery. For purification of rat cerebellar NOS, affinity chromatography with 2', 5'-ADP agarose column provided a 2646 fold purification of enzyme activity with a 688 pmol.ml-1.min-1 and 27% recovery. The purified rat and porcine cerebellar NOS constituted a single band on SDS/PAGE at about 160,000.

CONCLUSION

A stable and special method for measuring NOS activity was established.

[Extraction of humic acid from drinking water in area with arsenosis in inner Mongolia and Taiwan and comparison of its spectrometry]

In order to study etiology of blackfoot disease in Taiwan and to explore whether it can occur in the area with arsenosis in Inner Mongolia in the future, chemical components of specimens of drinking water from Taiwan and Inner Mongolia were determined and compared with infrared (IR), ultra-violet (UV) spectrometry and fluorescence spectrometry. Humic acid was extracted from the water samples by XAD-7 ion-exchange resin and Sephadex G-25 gel filtration chromatography, respectively, yielding the same results. Studies showed arsenic and humic acid levels in water samples both from Taiwan and Inner Mongolia all were higher, and their fluorescence and UV-spectra were similar, except a small difference in their IR spectra. Their effects on environment are under further studies.

Duplication of a gene-rich cluster between 16p11.1 and Xq28: a novel pericentromeric-directed mechanism for paralogous genome evolution

We have identified a 26.5 kb gene-rich duplication shared by human Xq28 and 16p11.1. Complete comparative sequence analysis of cosmids from both loci has revealed identical Xq28 and 16p11.1 genomic structures for both the human creatine transporter gene (SLC6A8) and five exons of the CDM gene (DXS1357E). Overall nucleotide similarity within the duplication was found to be 94.6%, suggesting that this interchromosomal duplication occurred within recent evolutionary time (7-10 mya). Based on comparisons between genomic and cDNA sequence, both the Xq28 creatine transporter and DXS1357E genes are transcriptionally active. Predicted translation of exons and RT-PCR analysis reveal that chromosome 16 paralogs likely represent pseudogenes. Comparative fluorescent in situ hybridization (FISH) analyses of chromosomes from various primates indicate that this gene-rich segment has undergone several duplications. In gorilla and chimpanzee, multiple pericentromeric localizations on a variety of chromosomes were found using probes from the duplicated region. In other species, such as the orangutan and gibbon, FISH signals were only identified at the distal end of the X chromosome, suggesting that the Xq28 locus represents the ancestral copy. Sequencing of the 16p 11.1/Xq28 duplication breakpoints has revealed the presence of repetitive immunoglobulin-like CAGGG pentamer sequences at or near the paralogy boundaries. The mobilization and dispersal of this gene-rich 27 kb element to the pericentromeric regions of primate chromosomes defines an unprecedented form of recent genome evolution and a novel mechanism for the generation of genetic diversity among closely related species.

A gene-rich cluster between the CD4 and triosephosphate isomerase genes at human chromosome 12p13

The genomic sequence of the human CD4 gene and its neighboring region, located at chromosome 12p13, was generated using the large-scale shotgun sequencing strategy. A total of 117 kb of genomic sequence and approximately 11 kb of cDNA sequence were obtained. Six genes, including CD4, triosephosphate isomerase, B3 subunit of G proteins (GNB3), and ubiquitin isopeptidase T (ISOT), with known functions, and two new genes with unknown functions were identified. Using a battery of strategies, the exon/intron boundaries, splice variants, and tissue expression patterns of the genes were determined. Various computer software was utilized for analyses of the DNA and amino acid sequences. The results of the analyses and sequence-based strategies for gene identification are discussed.

The value of Tc-99m MIBI SPECT during isosorbide dinitrate infusion in assessment of viable myocardium in patients with myocardial infarction

Tc-99m MIBI myocardial SPECT has shown promise for evaluation of coronary artery disease. But its role in predicting myocardial viability is still under investigation. The purpose of this study was to evaluate the value of Tc-99m MIBI myocardial SPECT during isosorbide dinitrate (ISDN) infusion in the assessment of myocardial viability. Thirty-seven patients with previous myocardial infarction (the infarct age ranged from < or = 30 days to 900 days) were studied, of them 13 patients had Tc-99m MIBI studies before and after coronary artery bypass grafting (CABG). The results showed that out of 134 segments with hypoperfusion at resting SPECT, 56 segments (41.8%) had an increase in Tc-99m MIBI uptake during ISDN infusion. Among them, 17 segments (30.4%) were normalized, 6 segments (10.7%) were significantly improved and 33 segments (58.9%) were improved. The degree of improvement in perfusion was related to the age of the myocardial infarction. In 13 patients with CABG, of 31 segments with improvement in perfusion post CABG, 25 segments (80.6%) showed perfusion improvement during ISDN infusion, and of 28 segments with improved wall motion post CABG, 23 segments (82.1%) showed improvement in perfusion during ISDN infusion. Tc-99m MIBI SPECT during ISDN infusion may therefore be a useful approach for assessing myocardial viability.

Mechanism of corepressor-mediated specific DNA binding by the purine repressor

The modulation of the affinity of DNA-binding proteins by small molecule effectors for cognate DNA sites is common to both prokaryotes and eukaryotes. However, the mechanisms by which effector binding to one domain affects DNA binding by a distal domain are poorly understood structurally. In initial studies to provide insight into the mechanism of effector-modulated DNA binding of the lactose repressor family, we determined the crystal structure of the purine repressor bound to a corepressor and purF operator. To extend our understanding, we have determined the structure of the corepressor-free corepressor-binding domain of the purine repressor at 2.2 A resolution. In the unliganded state, structural changes in the corepressor-binding pocket cause each subunit to rotate open by as much as 23 degrees, the consequences of which are the disengagement of the minor groove-binding hinge helices and repressor-DNA dissociation.

130 kb of DNA sequence reveals two new genes and a regional duplication distal to the human iduronate-2-sulfate sulfatase locus

Deficiency of IDs activity results in Hunter Syndrome (mucopolysaccharidosis type II), a fatal X-linked recessive disorder. We report characterization of 28 cosmids around the IDS locus in Xq28. Four overlapping cosmids have been sequenced in their entirety generating a 130-kb contig. These studies show the fine structure of the IDS gene and identify an IDS pseudogene-like structure located 20 kb distal to the active gene. Two novel genes have also been identified in this sequence, and one of these genes is also locally duplicated. Both homologs are expressed, and a number of alternative transcript products have been characterized. The presence of a highly conserved pseudogene-like structure within a larger duplicated region close to the IDS gene has significant implications for the study of mutations at this locus.

[Trigeminal neuralgia caused by microvascular compression of perforation type]

Of 512 patients of trigeminal neuralgia who had undergone microvascular decompression through a retromastoid craniotomy, 4 were caused by microvascular compression of perforation type. In 3 patients, the perineurium of trigeminal nerve was cut longitudinally, the nerve-tract was separated, the perforating blood vessel was pushed to the distal end, and the vessel was made to leave the nerve sensitive area and then decompression materials were put between the separated nerve-tract. The patients were pain-free and the facial sensation was preserved after operation, and no recurrence occurred in 1 to 3 years after operation. The authors realized that there is a sensitive area near the trigeminal nerve sensory root entry zone. When the blood vessel compresses the sensitive area, trigeminal neuralgia is induced, whereas the vessel decompresses the area, the pain is free. So it is a good evidence for the microvascular compression theory and it is more important than the non-perforation type.

[Some new concepts of cardiac myxoma]

The surgical treatment of cardiac myxoma in 211 consecutive cases (single tumor in 204 cases, multiple in 7, and recurrent in 3) from Dec. 1975 through Dec. 1993 was reviewed. Totally 228 myxomas were found and 215 operations performed. Data from this series and literature show that there were some complicated cases so that cardiac myxoma can not be simply regarded as a benign tumor only, but may be classified into two kinds: simple (or sporadic) cardiac myxoma and complicated cardiac myxoma. The latter includes myxoma complex, familial myxoma, and myxoma from multicenters. The clinical features, main points of diagnosis and surgery are concisely summarized.

Tn916 target DNA sequences bind the C-terminal domain of integrase protein with different affinities that correlate with transposon insertion frequency

The conjugative transposon Tn916 inserts with widely different frequencies into a variety of target sites with related nucleotide sequences. The binding of chimeric proteins, consisting of maltose-binding protein fused to Tn916 integrase, to three different target sequences for Tn916 was examined by DNase I protection experiments. The C-terminal DNA binding domain of the Tn916 integrase protein was shown to protect approximately 40 bp, spanning target sites in the orfA and cat genes of the plasmid pIP501 and in the cylA gene of the plasmid pAD1. Competition binding assays showed that the affinities of the three target sites for Tn916 integrase varied over a greater than 3- but less than 10-fold range and that the cat target site bound integrase at a lower affinity than did the other two target sites. A PCR-based assay for transposition in Escherichia coli was developed to assess the frequency with which a defective minitransposon inserted into each target site. In these experiments, integrase provided in trans from a plasmid was the sole transposon-encoded protein present. This assay detected transposition into the orfA and cylA target sites but not into the cat target site. Therefore, the frequency of transposon insertion into a particular target site correlated with the affinity of the target for the integrase protein. Sequences within the target fragments similar to known Tn916 insertion sites were not protected by integrase protein. Analysis ot he electrophoretic behavior of circularly permuted sets of DNA fragments showed that all three target sites contained structural features consistent with the presence of a static bend, suggesting that these structural features in addition to the primary nucleotide sequence are necessary for integrase binding and, thus, target site activity.

The gene for a human microfibril-associated glycoprotein is commonly deleted in Smith-Magenis syndrome patients

Smith-Magenis syndrome (SMS) is a clinically recognizable multiple congenital anomaly/mental retardation syndrome associated with deletion of chromosome 17p11.2. Here we report the identification of a novel gene encoding a human microfibril-associated glycoprotein (MFAP4), which has been mapped to the SMS region. A full-length cDNA corresponding to this gene has been sequenced, and reveals a coding region of 255 amino acids. MFAP4 has a fibrinogen-like domain and shares a high level of sequence homology to a fragment of a bovine 36 kDa microfibril-associated glycoprotein. The N-terminus of the protein bears an Arg-Gly-Asp sequence that serves as the ligand motif for cell surface receptor integrin. These structural features of MFAP4 suggest that it is an extracellular matrix protein involved in cell adhesion or intercellular interactions. Deletion analysis has been conducted on 31 SMS patients by polymerase chain reaction and Southern analysis of somatic cell hybrids retaining the del(17)(p11.2) chromosome or by fluorescence in situ hybridization. The MFAP4 locus is deleted in 30 of 31 SMS patients. Thus, the function of this gene must be considered in the pathogenesis of SMS. Given our previous hypothesis that SMS is a contiguous gene syndrome, complete and exhaustive definition of the critical deletion interval and a thorough phenotype-genotype correlation is required to demonstrate the role and importance of the MFAP4 gene in SMS.

Complete sequence of a 38.4-kb human cosmid insert containing the polymorphic marker DXS455 from Xq28

The complete DNA sequence of a cosmid mapping to human Xq28 (DXS455) has been determined using a shotgun approach (genbank accession number: L31948). The cosmid insert is 38.4 kb in length, and contains several repetitive sequences, including a highly repetitive region located in a fragment previously shown to contain a polymorphic VNTR locus, as well as short di- and tri-nucleotide repeats. In addition to the previously known VNTR locus, a CA-repeat and an unusual 800-bp repetitive region have been found to be polymorphic. The repeated sequence mapping to the site of the VNTR locus spans 480 bp in the cosmid. In addition to several AT-dinucleotide stretches, this repeat has four copies of a 25 bp repeat unit and flanking sequences similar to this 25-mer. No expressed sequences have so far been identified in this cosmid.

Developmental changes in the distribution of pro-opiomelanocortin and prolactin mRNA in the pituitary of the ovine fetus and lamb

Ontogenic changes in pituitary pro-opiomelanocortin (POMC) mRNA and prolactin (PRL) mRNA were examined during gestation and early neonatal life using in situ hybridization histochemistry. Pituitaries were harvested from fetuses at days 60-80, 100-120, 135-140 and 142-143 of gestation and at term, and from lambs at days 1-7 and 30-60 of age and adults. POMC mRNA, present by day 60, rose during mid- and late gestation. Concurrently there was a change in corticotroph distribution, resulting in a relatively greater quantity of POMC mRNA at the base of the pars distalis. At term, there was a significant (P < 0.05) further elevation of POMC mRNA. POMC mRNA levels remained high in the newborn lamb but decreased in the adult. Cells in the pars intermedia expressed large amounts of POMC mRNA early in fetal life and this pattern persisted throughout gestation and into the neonatal period. Changes in the expression of the POMC gene correlated closely with the presence of immunoreactive (ir)ACTH in the pituitary; in fetuses the proportion of irACTH-positive cells rose to 10% of pars distalis cells by day 100 and did not change significantly thereafter. The lactotrophs contained PRL mRNA by day 60, and the quantity increased towards parturition (P < 0.05). PRL mRNA subsequently decreased in the neonate, but rose as the lamb matured. These results indicate that in the fetal pituitary: (1) the POMC gene is highly expressed during gestation in both the pars distalis and the pars intermedia, (2) changes in the amounts of POMC mRNA and PRL mRNA in the pars distalis correlate with the distribution of irACTH and irPRL respectively, and (3) POMC mRNA is distributed primarily in the inferior aspect of the pars distalis, and in this region its quantity is highest immediately prior to parturition.

Mutagenesis of amino acid residues required for binding of corepressors to the purine repressor

The corepressor-binding domain of the Escherichia coli purine repressor (PurR) is homologous with several periplasmic sugar-binding proteins. Four amino acids in PurR were investigated for a role in binding of corepressors. Three of the residues, Asp146, Arg196 and Asp275, are conserved in periplasmic binding proteins for ribose, glucose/galactose, and arabinose and function to bind sugars. A fourth amino acid, Trp147, required for corepressor binding to PurR, corresponds to residues in glucose/galactose, ribose, and arabinose that also have a role in sugar binding. The four mutations that were constructed perturbed the binding of both hypoxanthine and guanine thus providing evidence for a single corepressor site/PurR subunit. The decreased corepressor binding affinity resulted in reduced affinity of mutant repressors for operator DNA in vitro and decreased capacity for repression in vivo. The corepressor-binding site in PurR appears to be similar to the conserved ligand-binding sites in the three periplasmic sugar-binding proteins and in the LacI family of repressors.