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Biomedical subjects

T K Ng

Publications and source records attributed to T K Ng.

At least 73 records · Page 4Linked to original sources
PubMed1982

Differential metabolism of cellobiose and glucose by Clostridium thermocellum and Clostridium thermohydrosulfuricum.

Clostridium thermohydrosulfuricum consumed glucose in preference to cellobiose as an energy source for growth. The rates of substrate uptake in glucose- and cellobiose-grown cell suspensions were 45 and 24 nmol/min per mg (dry weight), respectively, at 65 degrees C. The molar growth yields (i.e., grams of cells per mole of glucose equivalents) were similar on cellobiose and glucose (19 and 16, respectively). Both glucose- and cellobiose-grown cells contained a glucose permease activity and high levels of hexokinase (greater 0.34 mumol/min per mg of protein at 40 degrees C). Growth on cellobiose was associated with induction of a cellobiose permease activity. In contrast, Clostridium thermocellum metabolized cellobiose in preference to glucose as an energy source and displayed lower growth rates on both substrates. The substrate uptake rates in cellobiose- and glucose-grown cell suspensions were 18 and 17 nmol/min per mg (dry weight), respectively. The molar yields were 38 on cellobiose and 20 on glucose. Extracts of glucose- and cellobiose-grown cells both contained cellobiose phosphorylase and phosphoglucomutase activities, whereas only glucose-grown cells contained detectable levels of glucose permease and hexokinase activities. The general catalytic and kinetic properties of the glucose- and cellobiose-catabolizing enzymes in the two species are described, and a model is proposed to distinguish differential saccharide metabolism by these thermophilic ethanologens.

Biological Transport↗
PubMed1982

Occupational stress and hypertension.

The Department of Occupational and Environmental Health in the Commonwealth Institute of Health and the University of Sydney has since 1977 been conducting a study of possible occupational factors in hypertension and in other precursors of coronary heart disease. The study arose out of claims by public service employees that the stress of their work was inducing these diseases. The study has two additional aims: prospective observation of progression of hypertension and associated cardiovascular risk variables in relation to evolving occupational conditions; and a trial of non-pharmacological modification of mild hypertension and associated variables through intervention by occupational nurses. A total of 4607 subject drawn from telecommunications and taxation offices in Sydney underwent medical screening before allocation, according to risk, into intervention and reference groups. Data acquisition included self-administration of two questionnaires, on personal, social, occupational and medical history, and on reaction to potential work stresses and to recent life events. Response to questions related to the coronary prone behaviour pattern was tested in a sub-set of the population against rating of the pattern by Rosenman and Friedman's interview method. The paper reports on method and preliminary description of the population.

Adult↗
PubMed1981

Purification and characterization of an endoglucanase (1,4-beta-D-glucan glucanohydrolase) from Clostridium thermocellum.

An endoglucanase (1,4-beta-D-glucan glucanohydrolase, EC 3.2.1.4) was purified from Clostridium thermocellum by procedures that included centrifugation, ultrafiltration, selective precipitation, ion-exchange Sephadex chromatography and preparative gel electrophoresis. The 22-fold-purified enzyme behaved as a homogeneous protein under non-denaturing conditions. The enzyme represented a significant component (greater than 25%) of total extracellular endoglucanase activity, but was purified in low yield by the procedures employed. The native molecular weight of the endoglucanase was determined by ultracentrifugational analysis, amino acid composition and polyacrylamide-gel electrophoresis, and varied between 83000 and 94000. The enzyme contained 11.2% carbohydrate and was isoelectric at pH 6.72. The pH and temperature optima of the endoglucanase were 5.2 and 62 degrees C respectively. The enzyme lacked cysteine and was low in sulphur-containing amino acids. The purified endoglucanase displayed: high activity towards carboxymethylcellulose, celloheptaose, cellohexaose and cellopentaose; low activity towards Avicel microcrystalline cellulose and cellotetraose; no detectable activity towards cellotriose or cellobiose; increased activity towards cello-oligosaccharides with increasing degree of polymerization. The internal glycosidic bonds of cello-oligosaccharides were cleaved by the enzyme in preference to external linkages. The apparent Michaelis constant ([S]0.5V) and Vmax. for cellopentaose and cellohexaose hydrolysis were 2.30 mM and 39.3 mumol/min per mg of protein, and 0.56 mM and 58.7 mumol/min per mg of protein, respectively.

Amino Acids↗
PubMed1981

Sickness absence, respiratory impairment and smoking in industry: an australian study.

A retrospective study of sickness absence, respiratory impairment and their relation to smoking habits was conducted among a heterogeneous population of 1867 staff members of 12 Australian organizations. Data on smoking habits were used to divide the sample into current cigarette smokers (n=392), ex-cigarette smokers (n=182) and those who had never smoked (n=714). Results of the health survey by self-administered questionnaire showed that the prevalence of respiratory symptoms was higher in cigarette smokers than in non-smokers both in men and women. Smoking was particularly related to frequency of cough, and sputum production. Wheezing showed a similar, though less marked, trend. The influence of smoking on the pulmonary function value, FEV1/FVC% was assessed in a group of 972 men and 297 women. Results of analysis of variance showed that ventilatory function was significantly impaired among smokers and ex-smokers. The sickness absence records of 826 cigarette smokers, ex-smokers and non-smokers were also compared. Both frequency and duration of sickness absence were greater in cigarette smokers and ex-smokers. Significant differences between these groups were confirmed in total as well as in certified absence. Among males, the average number of days off work was 1.59 times greater in male smokers than in male non-smokers, and 1.36 times greater for female subjects who smoked. The epidemiological implications of such findings await further research. However, the consequences for the individual, industry and the general community are apparent.

Absenteeism↗
PubMed1981

Thermophilic ethanol fermentations.

Thermophilic ethanol fermentations are of interest to industrial alcohol production because both the pentose and hexose fraction of biomass can be directly fermented in high yield (i.e., mol ethanol/mol substrate consumed), and because of potential novel process features associated with high temperature operation. As a net result, the co-culture cellulose fermentations described here may have the potential to convert more substrate to alcohol than some other bioconversion systems described [see Figure 11, (2)]. However, considerably more fundamental and applied research is required before realistic economic assessments can be made. Detailed analysis of the data presented above suggests key control parameters for thermophilic ethanol production (see Table IX). Understanding in detail the physiological and biochemical features that control rate limitation, yield limitation and concentration limitation appears to me as trends for future applied and fundamental studies on thermophilic ethanologenic bacteria. It is worth noting from the data reviewed here that understanding control of any one of these 3 major limitations is complex and multi-faceted. Indeed, improvement of ethanol tolerance (i.e. the ability to produce greater than 1% ethanol at high rates) in these bacteria appears to involve challenges by all three limitations. Furthermore, the biochemical basis for alcohol tolerance in thermophilic ethanologens appears to vary in different species. For example, the ethanol dehydrogenase of C. thermocellum is inhibited by physiological concentrations of alcohol (i.e. 1%) whereas, the reversible activity of T. brockii or C. thermohydrosulfuricum enzyme is increased by higher solvent concentration (greater than 5%).

Bacteria↗
PubMed1981

Ethanol Production by Thermophilic Bacteria: Fermentation of Cellulosic Substrates by Cocultures of Clostridium thermocellum and Clostridium thermohydrosulfuricum.

The fermentation of various saccharides derived from cellulosic biomass to ethanol was examined in mono- and cocultures of Clostridium thermocellum strain LQRI and C. thermohydrosulfuricum strain 39E. C. thermohydrosulfuricum fermented glucose, cellobiose, and xylose, but not cellulose or xylan, and yielded ethanol/acetate ratios of >7.0. C. thermocellum fermented a variety of cellulosic substrates, glucose, and cellobiose, but not xylan or xylose, and yielded ethanol/acetate ratios of approximately 1.0. At nonlimiting cellulosic substrate concentrations ( approximately 1%), C. thermocellum cellulase hydrolysis products accumulated during monoculture fermentation of Solka Floc cellulose and included glucose, cellobiose, xylose, and xylobiose. A stable coculture that contained nearly equal numbers of C. thermocellum and C. thermohydrosulfuricum was established that fermented a variety of cellulosic substrates, and the ethanol yield observed was twofold higher than in C. thermocellum monoculture fermentations. The metabolic basis for the enhanced fermentation effectiveness of the coculture on Solka Floc cellulose included: the ability of C. thermocellum cellulase to hydrolyze alpha-cellulose and hemicellulose; the enhanced utilization of mono- and disaccharides by C. thermohydrosulfuricum; increased cellulose consumption; threefold increase in the ethanol production rate; and twofold decrease in the acetate production rate. The coculture actively fermented MN300 cellulose, Avicel, Solka Floc, SO(2)-treated wood, and steam-exploded wood. The highest ethanol yield obtained was 1.8 mol of ethanol per mol of anhydroglucose unit in MN300 cellulose.

Journal Article↗
PubMed1981

Comparison of Extracellular Cellulase Activities of Clostridium thermocellum LQRI and Trichoderma reesei QM9414.

The crude extracellular cellulase of Clostridium thermocellum LQRI (virgin strain) was very active and solubilized microcrystalline cellulose at one-half the rate observed for the extracellular cellulase of Trichoderma reesei QM9414 (mutant strain). C. thermocellum cellulase activity differed considerably from that of T. reesei as follows: higher endoglucanase/exoglucanase activity ratio; absence of extracellular cellobiase or beta-xylosidase activity; long-chain oligosaccharides instead of short-chain oligosaccharides as initial (15-min) hydrolytic products on microcrystalline cellulose; mainly cellobiose or xylobiose as long-term (24-h) hydrolysis products of Avicel and MN300 or xylan; and high activity and stability at 60 to 70 degrees C. Under optimized reaction conditions, the kinetic properties (V(max), 0.4 mumol/min per mg of protein; energy of activation, 33 kJ; temperature coefficient, 1.8) of C. thermocellum cellulose-solubilizing activity were comparable to those reported for T. reesei, except that the dyed Avicel concentration at half-maximal velocity was twofold higher (182 muM). The cellulose-solubilizing activity of the two crude cellulases differed considerably in response to various enzyme inhibitors. Most notably, Ag and Hg effectively inhibited C. thermocellum but not T. reesei cellulase at <20 muM, whereas Ca, Mg, and Mn inhibited T. reesei but not C. thermocellum cellulase at >10 mM. Both enzymes were inhibited by Cu (>20 mM), Zn (>1.0 mM), and ethylene glycol-bis(beta-aminoethyl ether)- N,N-tetraacetic acid (>10 mM). T. reesei but not C. thermocellum cellulose-solubilizing activity was 20% inhibited by glucose (73 mM) and cellobiose (29 mM). Both cellulases preferentially cleaved the internal glycosidic bonds of cellooligosaccharides. The overall rates of cellooligosaccharide degradation were higher for T. reesei than for C. thermocellum cellulase, except that the rates of conversion of cellohexaose to cellotriose were equivalent.

Journal Article↗
PubMed1976

Some observations on the needs of ergonomics in industries in Hong Kong.

The author's interest in ergonomics lies in the common ground it shares with occupational health, since ergonomics aims to make work easier, safer, and more productive and to promote efficiency, comfort, and health. In Hong Kong, owing to lack of natural resources and guaranteed markets, industrialization has not taken a smooth course. Only light industries exist, and one industry flourishes after another. Occupational health and safety tends to be neglected not only by the employers but by the employees. The government becomes the promoter of labor legislation. There is almost no information on occupational diseases. There are some elementary official statistics on occupational accidents. There is practically no research activities on this area going on. There is a very critical lack of occupational health, workers in Hong Kong. Ergonomics may help in improving the present situation because its aims are more positive to the industrialists and the workers who should be converted into educated consumers of ergonomics. In the long run, advancement in occupational health and safety practice will be made.

Accidents, Occupational↗