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Biomedical subjects

J Tang

Publications and source records attributed to J Tang.

At least 433 records · Page 24Linked to original sources
PubMed1993

Conformational instability of the N- and C-terminal lobes of porcine pepsin in neutral and alkaline solutions.

Pepsin contains, in a single chain, two conformationally homologous lobes that are thought to have been evolutionarily derived by gene duplication and fusion. We have demonstrated that the individual recombinant lobes are capable of independent folding and reconstitution into a two-chain pepsin or a two-chain pepsinogen (Lin, X., et al., 1992, J. Biol. Chem. 267, 17257-17263). Pepsin spontaneously inactivates in neutral or alkaline solutions. We have shown in this study that the enzymic activity of the alkaline-inactivated pepsin was regenerated by the addition of the recombinant N-terminal lobe but not by the C-terminal lobe. These results indicate that alkaline inactivation of pepsin is due to a selective denaturation of its N-terminal lobe. A complex between recombinant N-terminal lobe of pepsinogen and alkaline-denatured pepsin has been isolated. This complex is structurally similar to a two-chain pepsinogen, but it contains an extension of a denatured pepsin N-terminal lobe. Acidification of the complex is accompanied by a cleavage in the pro region and proteolysis of the denatured N-terminal lobe. The structural components that are responsible for the alkaline instability of the N-terminal lobe are likely to be carboxyl groups with abnormally high pKa values. The electrostatic potentials of 23 net carboxyl groups in the N-terminal domain (as compared to 19 in the C-terminal domain) of pepsin were calculated based on the energetics of interacting charges in the tertiary structure of the domain. The groups most probably causing the alkaline denaturation are Asp11, Asp159, Glu4, Glu13, and Asp118.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Method for sequencing synthetic oligodeoxynucleotide phosphorothioates.

Sequencing of oligodeoxynucleotide phosphorothioate by a modified Sanger method of sequencing is described. The procedure involves ligation of synthetic oligodeoxynucleotide phosphorothioate to an oligodeoxynucleotide, referred to here as "helper oligonucleotide." The helper oligonucleotide has a region which is complementary to T7 primer. By using DNA polymerase and nucleoside triphosphate mixture, 5'-labeled T7 primer is extended onto ligated oligodeoxynucleotide phosphorothioate, which is then analyzed on gel electrophoresis.

Base Sequence↗
PubMed1993

Quality assurance in the biological monitoring of lead exposure in China.

Based on the statistical data of the nationwide occupational diseases reporting in 1986-1988, lead poisoning stood the first place of chronic occupational poisonings in China. Biological monitoring of lead exposure is of paramount importance in both occupational and environmental health. In order to ensure lead testing data valid enough for taking actions of prevention and control, a quality assurance scheme including selection of reliable analytical techniques, establishing reference laboratory, application of standard reference materials, and conducting internal and external quality control program was implemented in China. Since the rigid assurance procedure was conducted during studies on "background levels of lead in non-exposure population" and "revision of the diagnostic criteria for lead", compatible and reliable results were obtained.

Aminolevulinic Acid↗
PubMed1993

Static morphometric bases for CT identification and evaluation of the outflow chamber of the left ventricle. Preliminary study in formalin-fixed heart.

A static morphometric study of the outflow chamber of the left ventricle (OCLV) was investigated in a series of 10 formalin-fixed hearts. A spatial reconstruction of the shape and the volume of the OCLV was carried out by means of a Somaton Plus TR4 Tomodensitometer (Siemens). The technic allows evaluation of the surface of the aortic and the mitral orifices and visualization of the three-dimensional OCLV and LV morphology, as well as calculation of their volumes. The limits of the technic in the dynamic study of the OCLV are presented.

Adult↗
PubMed1993

Meprin activity in rats with experimental renal disease.

Activity of renal meprin, a membrane-bound proteinase in the proximal tubule brush border, was measured in normal rats and in two disease groups: chronic puromycin aminonucleoside nephropathy for 12 weeks and streptozocin-induced diabetes for 6 months. Enzyme activity in kidney homogenates was assayed using azocasein as substrate. The mean activity of mephrin was 3.22 +/- 0.34 U/g kidney weight in normal rats. In diabetic animals, enzyme activity was 8.58 +/- 2.11 U/g kidney weight, P < 0.01. In contrast, meprin activity was decreased in rats with puromycin-induced glomerulopathy, 2.13 +/- 0.17 U/g kidney weight, P < 0.01. These findings indicate that meprin activity is elevated in experimental diabetes. Diminished activity of this luminal membrane enzyme in puromycin aminonucleoside nephropathy may contribute to renal injury in this disease model associated with massive urinary protein excretion.

Animals↗
PubMed1993

Regional distribution in the rat central nervous system of a mRNA encoding a portion of the cardiac sodium/calcium exchanger isolated from cerebellar granule neurons.

The cardiac Na+/Ca2+ exchanger is a bidirectional electrogenic ion transporter that exchanges three Na+ ions for each Ca2+ ion and plays a critical role in returning sarcolemma Ca2+ concentrations to their resting levels. Because of the importance that the Na+/Ca2+ exchanger may play in maintaining neuronal Ca2+ homeostasis in the central nervous system, we subcloned a 456 bp portion of the Na+/Ca2+ exchanger cDNA from RNA isolated from primary cultures of rat cerebellar granule neurons using the polymerase chain reaction (PCR). This cDNA fragment was sequenced and shown to share 91.4% sequence identity with the human and 88% sequence identity with the canine cardiac Na+/Ca2+ exchangers. The PCR amplification product was used to analyze the distribution of this portion of the Na+/Ca2+ exchanger mRNA in various regions of the CNS by both Northern blotting and in situ hybridization histochemistry. The Northern analysis showed that the rank order of abundance of this mRNA was: hippocampus > cortex > cerebellum > hypothalamus > midbrain > striatum. The in situ hybridization data indicated that the corresponding mRNA containing this portion of the exchanger was present in numerous brain regions including multiple cortical layers, the hippocampus, septal nuclei, various thalamic nuclei, cerebellum, hypothalamus, olfactory bulb, brainstem, in various regions of the thoracic spinal cord and to a lesser extent in the striatum. The differential distribution of the mRNA as revealed by the in situ hybridization pattern suggests that either additional molecular variants exist or that different Na+/Ca2+ exchange mechanisms may be operative in those cell types that contain low amounts of this fragment of the exchanger mRNA.

Animals↗
PubMed1993

Entrapment and inhibition of human immunodeficiency virus proteinase by alpha 2-macroglobulin and structural changes in the inhibitor.

The inhibitory effect of alpha 2-macroglobulin (alpha 2M), a major plasma proteinase inhibitor, on human immunodeficiency virus (HIV) proteinase was investigated. The activity of HIV proteinase toward the Moloney murine sarcoma virus-derived gag protein (a high-molecular-mass substrate) was found to be inhibited by alpha 2M at pH 5.5-7.4. On the other hand, the activity toward the B chain of oxidized insulin (a low-molecular-mass substrate) was scarcely inhibited. The complex of alpha 2M and HIV proteinase was isolated by gel filtration and the enzyme was shown to be significantly protected by the complex formation from autoinactivation under nonreducing conditions. The stoichiometry of the complex formation was found to be 2:1 (enzyme: alpha 2M, mol/mol). These results demonstrate the entrapment and concomitant inhibition of HIV proteinase by alpha 2M.

Amino Acid Sequence↗
PubMed1993

Intracellular diversion of glycoprotein GP160 of human immunodeficiency virus to lysosomes as a strategy of AIDS gene therapy.

A potential gene therapy strategy against human immunodeficiency virus (HIV-1) is to disrupt the intracellular transport of viral proteins. We report here the binding and transporting of HIV-1 glycoprotein gp160 to lysosomes as a result of the expression of fusion genes consisting of soluble CD4 and lysosome targeting domains. The effective lysosome targeting domain tested includes a lysosomal protease zymogen, procathepsin D, and the COOH-terminal domains of three lysosome membrane proteins: lamp-1, lamp-2, and lysosomal acid phosphatase. We demonstrated that cell fusion (syncytium), caused by the transport of gp160 to the surface of HeLa-CD4+ cells, was completely abolished by the expression of these fusion genes. The lysosomal localization of gp160 in HeLa cells coexpressing CD4-fusion genes was also established. From pulse-chase experiments, we observed that gp160 and the fusion proteins were degraded, as expected of lysosomal activities. Additionally, T lymphoblastoid cells transiently and permanently expressing these fusion genes strongly retarded the propagation of human immunodeficiency virus type 1. Thus, these fusion genes can deprive HIV of newly synthesized envelope protein gp160 for the assembly of new virions and are potentially useful in gene therapy against AIDS.

Acid Phosphatase↗
PubMed1993

An enhancer screen identifies a gene that encodes the yeast U1 snRNP A protein: implications for snRNP protein function in pre-mRNA splicing.

In an enhancer screen for yeast mutants that may interact with U1 small nuclear RNA (snRNA), we identified a gene that encodes the apparent yeast homolog of the well-studied human U1A protein. Both in vitro and in vivo, the absence of the protein has a dramatic effect on the activity of U1 snRNP containing the mutant U1 snRNA used in the screen. Surprisingly, the U1A gene is inessential in a wild-type U1 RNA background, as growth rate and the splicing of endogenous pre-mRNA transcripts are normal in these strains that lack the U1A protein. Even in vitro, the absence of the protein has little effect on splicing. On the basis of these observations, we suggest that a principal role of the U1A protein is to help fold or maintain U1 RNA in an active configuration.

Alleles↗
PubMed1993

Attending to auditory filters that were not stimulated directly.

The effectiveness of two types of tonal cues for reducing frequency uncertainty was studied in a tonal detection-in-noise task. Signals varied at random from trial to trial over the range 750-3000 Hz. The three conditions included: (1) maximum uncertainty in which there were no cues; (2) minimal uncertainty in which "iconic cues" were identical to the signal to be detected; and (3) partial uncertainty in which "relative cues" were set to 2/3 of the signal frequency, i.e., at the musical 5th. Results show that relative cues and iconic cues were both effective in reducing uncertainty compared to the no-cue condition, but that performance with relative cues was poorer than with iconic cues by 1.4 dB. In addition, a modified probe-signal method was used to estimate the widths of the subjective listening bands. Application of a model of the auditory filter [R. Patterson and B. C. J. Moore, Frequency Selectivity in Hearing, edited by B. C. J. Moore (Academic, New York, 1986)] to these data showed that the subjective listening bands used with iconic cues were similar in width to typical measures of the critical band but that the bands used with relative cues were wider by a factor of roughly 1.6.

Acoustic Stimulation↗
PubMed1993

Genetic analysis of laminin A reveals diverse functions during morphogenesis in Drosophila.

In order to dissect the functions of laminin A in vivo, we have undertaken a molecular and genetic characterization of the laminin A subunit (lamA) gene in Drosophila. Sequence analysis predicts a multidomain structure similar to mammalian homologs. We generated a series of complete and partial loss-of-function mutant alleles of the lamA gene; complete loss-of-function mutations lead to late embryonic lethality. Certain combinations of partial loss-of-function lamA alleles give rise to escaper adults, which have rough eyes associated with changes in cell fate and pattern, misshapen legs and defects in wing structure. These phenotypes suggest that laminin A has diverse functions during morphogenesis in Drosophila.

Animals↗
PubMed1993

A new model for the study of mild diabetes during pregnancy. Syngeneic islet-transplanted STZ-induced diabetic rats.

Diabetes during pregnancy carries short- and long-term consequences for the offspring. Improved obstetrical and diabetic care has resulted in decreased morbidity and mortality in the neonate of the diabetic mother. Mild hyperglycemia is still found in both IDDM pregnant women and women with GDM. The long-term consequences of exposure to mild hyperglycemia in utero remain to be determined. In an effort to develop an appropriate animal model of mild diabetes during pregnancy, we mated female STZ-induced diabetic rats previously transplanted with specific numbers of islets of Langerhans (2500, 1000, 700, or 500 islets). Diabetic and nondiabetic sham-transplanted control groups also were studied. During pregnancy, the plasma glucose levels in the diabetic rats and the group receiving 500 islets (26.5 +/- 1.1 and 10.0 +/- 0.8 mM, respectively) were significantly greater than in control animals (5.4 +/- 0.5 mM, P < 0.0001). The mean glucose levels in rats receiving 700 or 1000 transplanted islets (6.8 +/- 0.2 and 6.5 +/- 0.2 mM) also were significantly greater than in control animals (P < 0.001). No difference was evident between control rats and the group receiving 2500 islets (5.8 +/- 0.2 mM). No gross congenital abnormalities were apparent in the offspring. The pup plasma glucose was significantly greater in the offspring of dams receiving either none (diabetic) or 500 islets (10.6 +/- 0.7 and 11.1 +/- 1.1 mM, respectively) compared with the offspring of nondiabetic control dams (4.4 +/- 0.3 mM, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Impeded progression of Friend disease in mice by an inhibitor of retroviral proteases.

The protease of the human immunodeficiency virus type 1 (HIV-1) is essential for the processing of GAG and POL polyproteins and maturation of the virus particles. Using recombinant protease and a truncated GAG polyprotein as substrate, we developed a Western blot assay for the evaluation of inhibitors of the enzyme. Two statine-based inhibitors of the enzyme, KH161 and KH164, were effective in blocking the replication of HIV-1 in acutely infected human T4 lymphoid cells, with potency approaching that of zidovudine (ZDV) when tested in parallel. In chronically infected cells, the production of infectious virus was inhibited by KH161 and KH164, while ZDV was ineffective. Both KH161 and KH164 were also active as antivirals against the replication of murine leukemia virus (MLV) in cultured mouse cells. In an animal model of a murine retroviral disease, KH164 was shown to inhibit in a dose-dependent manner the progression of the disease induced by Friend virus complex (a mixture of Friend MLV and spleen focus-forming virus). The results suggest that the progression of the acquired immune deficiency syndrome (AIDS) may be impeded by inhibitors of HIV-1 protease.

Amino Acid Sequence↗