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Biomedical subjects

H Fu

Publications and source records attributed to H Fu.

At least 163 records · Page 9Linked to original sources
PubMed1990

Reversible ADP-ribosylation is demonstrated to be a regulatory mechanism in prokaryotes by heterologous expression.

The primary product of biological nitrogen fixation, ammonia, reversibly regulates nitrogenase activity in a variety of diazotrophs by a process called "NH4(+)-switch-off/on." Strong correlative evidence from work in Azospirillum lipoferum and Rhodospirillum rubrum indicates that this regulation involves both the inactivation of dinitrogenase reductase by dinitrogenase reductase ADP-ribosyltransferase and the reactivation by dinitrogenase reductase activating glycohydrolase. The genes encoding these two enzymes, draT and draG, have been cloned from these two organisms, so that direct genetic evidence can be marshaled to test this model in vivo. The draT/G system has been transferred to and monitored in the enteric nitrogen-fixing bacterium Klebsiella pneumoniae, an organism normally devoid of such a regulatory mechanism. The expressed draT and draG genes allowed K. pneumoniae to respond to NH4Cl with a reversible regulation of nitrogenase activity that was correlated with the reversible ADP-ribosylation of dinitrogenase reductase in vivo. Thus, the expression of draT and draG genes in K. pneumoniae is necessary and sufficient to support NH4(+)-switch-off/on, and ADP-ribosylation serves as a reversible regulatory mechanism for controlling nitrogenase activity in prokaryotes.

ADP Ribose Transferases↗
PubMed1989

Ammonium inhibition of nitrogenase activity in Herbaspirillum seropedicae.

The effect of oxygen, ammonium ion, and amino acids on nitrogenase activity in the root-associated N2-fixing bacterium Herbaspirillum seropedicae was investigated in comparison with Azospirillum spp. and Rhodospirillum rubrum. H. seropedicae is microaerophilic, and its optimal dissolved oxygen level is from 0.04 to 0.2 kPa for dinitrogen fixation but higher when it is supplied with fixed nitrogen. No nitrogenase activity was detected when the dissolved O2 level corresponded to 4.0 kPa. Ammonium, a product of the nitrogenase reaction, reversibly inhibited nitrogenase activity when added to derepressed cell cultures. However, the inhibition of nitrogenase activity was only partial even with concentrations of ammonium chloride as high as 20 mM. Amides such as glutamine and asparagine partially inhibited nitrogenase activity, but glutamate did not. Nitrogenase in crude extracts prepared from ammonium-inhibited cells showed activity as high as in extracts from N2-fixing cells. The pattern of the dinitrogenase and the dinitrogenase reductase revealed by the immunoblotting technique did not change upon ammonium chloride treatment of cells in vivo. No homologous sequences were detected with the draT-draG probe from Azospirillum lipoferum. There is no clear evidence that ADP-ribosylation of the dinitrogenase reductase is involved in the ammonium inhibition of H. seropedicae. The uncoupler carbonyl cyanide m-chlorophenylhydrazone decreased the intracellular ATP concentration and inhibited the nitrogenase activity of whole cells. The ATP pool was not significantly disturbed when cultures were treated with ammonium in vivo. Possible mechanisms for inhibition by ammonium of whole-cell nitrogenase activity in H. seropedicae are discussed.

Adenosine Diphosphate Ribose↗
PubMed1989

Smelting, underground mining, smoking, and lung cancer: a case-control study in a tin mine area.

An increased risk of lung cancer in the Dachang tin mine of Guangxi has been reported. To investigate the factors contributing to the excessive risk of lung cancer, we conducted a matched case-control study in the mine area and analyzed the effects of multiple factors, such as living and housing conditions, occupational exposure, and smoking, with the methods of conditional logistic regression. The case series consisted of 69 patients with primary bronchial cancer, 55 of whom had died. The control series consisted of 138 individuals, 55 of whom were decreased. The results showed that the factors contributing to the excessive risk of lung cancer in the mine area related mainly to occupational exposure. The significant risk factors were time of exposure to smelting, time of exposure to underground mining, and age at which underground mining was begun. In study model II where living controls were used, daily consumption of cigarettes was an additional risk factor. Furthermore, there was a synergistic action among these factors. The relation of the risk factors to lung cancer is discussed.

Case-Control Studies↗
PubMed1989

[Standard of transesophageal atrial pacing to diagnose dual atrioventricular node pathway].

In order to assess the diagnostic methods of dual atrioventricular node pathway (DAVNP), we performed transesophageal atrial pacing in 58 patients with palpitation. These patients were classified into two groups, group A comprising 40 patients without broken A-V conduction curve during pacing, compared with group B of 18 patients with broken A-V conduction curve. In our study, both atypical Wenckebach cycle and 3:2 A-V conduction during the increment atrial pacing (IAP) had no significant difference between the two groups (P greater than 0.05). The maximum increments of SR interval in Wenckebach cycle of group A and B during pacing (Wenckebach delta SRmax) were 83.59 +/- 20.92 ms and 125.00 +/- 32.52 ms respectively (P less than 0.001) and at the cut-off point of Wenckebach delta SRmax at 120 ms the specificity and positive predicative value were very high (96.88% and 90.91%), but sensitivity was not so high (71.43%). The minimum increments of RS interval (delta RSmin) in a greater change of SR interval showed a significant difference between the two groups and the specificity and positive predicative value were also high, but the sensitivity was not so high, either (78.57%). We conclude that the diagnostic value of both Wenckebach delta SRmax and delta RSmin, when the SR interval is of greater change during pacing to the DAVNP, is rather significant. As the sensitivity is very low, isolated atypical Wenckebach phenomenon is not as reliable a diagnostic criterion to the DAVNP as previously supposed.

Adult↗
PubMed1986

Regulation of nitrogenase activity by ammonium chloride in Azospirillum spp.

Ammonium chloride (greater than or equal to 0.05 mM) effectively and reversibly inhibited the nitrogenase activity of Azospirillum brasilense, Azospirillum lipoferum and Azospirillum amazonense. The glutamine synthetase inhibitor L-methionine-DL- sulfoximine abolished this "switch-off" in A. lipoferum and A. brasilense, but not in A. amazonense. Azaserine, an inhibitor of glutamate synthase, inhibited nitrogenase activity itself. This provides further evidence for glutamine as a metabolite of regulatory importance in the NH4+ switch-off phenomenon. In A. brasilense and A. lipoferum, a transition period before the complete inhibition of nitrogenase activity after the addition of 1 mM ammonium chloride was observed. The in vitro nitrogenase activity also was decreased after treatment with ammonium. During sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a second dinitrogenase reductase (Fe protein) subunit appeared, which migrated in coincidence with the modified subunit of the inactive Fe protein of the nitrogenase of Rhodospirillum rubrum. After the addition of ammonium 32P was incorporated into this subunit of the Fe protein of A. brasilense. In A. amazonense, the inhibition of nitrogenase activity by ammonium was only partial, and no transition period could be observed. The in vitro nitrogenase activity of ammonium-treated cells was not decreased, and no evidence for a modified Fe protein subunit was found. Nitrogenase extracts of A. amazonense were active and had an Fe protein that migrated as a close double band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Ammonium Chloride↗
PubMedDate not supplied

One-step production of D-p-hydroxyphenylglycine by recombinant Escherichia coli strains.

The gene encoding D-hydantoinase from Agrobacterium radiobacter NRRL B11291 was successfully cloned by use of polymerase chain reaction. A positive clone was scored, and its nucleotide sequence was further analyzed. The analysis by deleting various lengths of nucleotides from the amino terminus of the open reading frame revealed the putative regions for promoter and RBS site. By highly expressing both D-hydantoinase and carbamoylase, recombinant Escherichia coli strains were able to convert DL-hydroxyphenyl hydantoin (DL-HPH) to D-p-hydroxyphenylglycine (D-HPG) with a conversion yield of 97%, accounting for productivity 5 times higher than that obtained by A. radiobacter NRRL B11291. Immobilizing the recombinant cells with kappa-carrageenan could also achieve a conversion of 93%, while A. radiobacter NRRL B11291 attained 20% within the same period of reaction time. These results illustrate the feasibility in employing recombinant E. coli to accomplish one-step conversion of DL-HPH to D-HPG. In the process of improving D-HPG production, D-hydantoinase activity was increased 2.57-fold but carbamoylase activity remained constant, which resulted in only a 30% increase in the reaction rate. It suggests that carbamoylase is the step setting the pace of the reaction. Since the reaction substrate is highly insoluble, achieving sufficient agitation appears to be an important issue in this heterogeneous system. This view is further supported by the study on repeated use of cells, which shows that to reach a conversion of more than 90% free cells can be recycled six times, whereas immobilized cells can be used only twice. In conclusion, the poor reusability of immobilized cells is due to the fouling on the gel surface.

Amidohydrolases↗
PubMedDate not supplied

Fatal occupational injuries in the construction industry of a new development area in east China, 1991 to 1997.

Two hundred thirty-five work-related deaths occurred in the construction industry in a new economic development area in eastern China between 1991 and 1997. These fatalities represented 55% of all occupational deaths. The average annual mortality rate was 51.5 per 100,000 construction workers. Falls were the leading cause of death (46.4%). Falls, collisions, struck by/against something, electrocutions, and excavation cave-ins were the main fatality antecedents, accounting for nearly 93.6% of all fatalities. The most common antecedents for incidents with multiple fatalities were falls, crane-related events, poisoning, and fire. These categories of antecedents were similar to those encountered in the construction industry in the United States. These data suggest that organizations need to focus on these event types when planning their prevention activities. Moreover, improved surveillance systems including computerized databases with narrative descriptions of injury events, antecedent factors, and person-time at-risk data are needed to target interventions more precisely.

Accidents, Occupational↗
PubMedDate not supplied

Analysis of 541 cases of occupational acute chemical injuries in a large petrochemical company in China.

The authors carried out a descriptive analysis of acute chemical intoxication in a large petrochemical corporation with 38,000 employees, located in a suburban district of Shanghai, China, to determine the chemicals involved and the primary causes of the incidents. Between 1977 and 1997, 350 cases of acute chemical-intoxication were recorded, resulting in a total of 541 workers with symptoms. Of these, 483 were male and 58, female, with over half the victims under 30 years old. Two hundred and seventy-five cases were serious enough to necessitate hospital admission. There were 266 cases of chemical irritation or inhalation responses (49.2%), 215 cases of mild chemical poisoning (39.7%), 31 cases of moderate poisoning (5.7%), and 29 cases resulting in critical injury (5.4%), including eight deaths (1.5%). The main causes of injury reported by patients were lack of training about safety (63%) and equipment failure (23%). The chemicals involved were asphyxiating gases (302 cases; 55.8%), irritating gases (111 cases; 20.5%), and other toxins. Intervention strategies for the prevention of acute chemical exposures were suggested to the corporation.

Accidents, Occupational↗
PubMedDate not supplied

The incidence of insulin-dependent diabetes mellitus in urban districts of Shanghai (1989-1993).

A retrospective study on the incidence of insulin-dependent diabetes mellitus (IDDM) among children aged 0-14 years was carried out from 1989-1993 in urban Shanghai, China. The average annual population at risk (0-14 yr) consisted of 1,401,664 children. All the cases were collected from the hospitals (primary source) and from primary and middle schools and kindergartens (second source) with independent validation of case ascertainment. There were 53 IDDM cases from the primary source, 23 from the secondary source, with a total of 58. The ascertainment corrected total number of IDDM cases was 67 by the capture-recapture method. The average crude annual incidence rate was 0.83 [95% confidence interval (CI) 0.61-1.04] and ascertainment corrected incidence rate 0.96 (95% CI 0.80-1.12) per 100,000. Peak incidence fell in 1992 and in the 9 year-old group. The incidence of childhood IDDM in the urban districts of Shanghai was reconfirmed to be the lowest in the world but by comparing the results of former investigations a trend was found of increasing incidence of IDDM.

Adolescent↗
PubMedDate not supplied

Contraceptive failure rates: new estimates from the 1995 National Survey of Family Growth.

CONTEXT: Unintended pregnancy remains a major public health concern in the United States. Information on pregnancy rates among contraceptive users is needed to guide medical professionals' recommendations and individuals' choices of contraceptive methods. METHODS: Data were taken from the 1995 National Survey of Family Growth (NSFG) and the 1994-1995 Abortion Patient Survey (APS). Hazards models were used to estimate method-specific contraceptive failure rates during the first six months and during the first year of contraceptive use for all U.S. women. In addition, rates were corrected to take into account the underreporting of induced abortion in the NSFG. Corrected 12-month failure rates were also estimated for subgroups of women by age, union status, poverty level, race or ethnicity, and religion. RESULTS: When contraceptive methods are ranked by effectiveness over the first 12 months of use (corrected for abortion underreporting), the implant and injectables have the lowest failure rates (2-3%), followed by the pill (8%), the diaphragm and the cervical cap (12%), the male condom (14%), periodic abstinence (21%), withdrawal (24%) and spermicides (26%). In general, failure rates are highest among cohabiting and other unmarried women, among those with an annual family income below 200% of the federal poverty level, among black and Hispanic women, among adolescents and among women in their 20s. For example, adolescent women who are not married but are cohabiting experience a failure rate of about 31% in the first year of contraceptive use, while the 12-month failure rate among married women aged 30 and older is only 7%. Black women have a contraceptive failure rate of about 19%, and this rate does not vary by family income; in contrast, overall 12-month rates are lower among Hispanic women (15%) and white women (10%), but vary by income, with poorer women having substantially greater failure rates than more affluent women. CONCLUSIONS: Levels of contraceptive failure vary widely by method, as well as by personal and background characteristics. Income's strong influence on contraceptive failure suggests that access barriers and the general disadvantage associated with poverty seriously impede effective contraceptive practice in the United States.

Abortion, Induced↗