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T Kwok

Publications and source records attributed to T Kwok.

At least 37 records · Page 2Linked to original sources
PubMed1998

Thermodynamics of the interaction of the Escherichia coli regulatory protein TyrR with DNA studied by fluorescence spectroscopy.

Fluorescence quenching was used to study the site-specific binding of the Escherichia coli regulatory protein TyrR to a fluoresceinated oligonucleotide (9F30A/30B) containing a TyrR binding site. The equilibrium constant for the interaction (KL) was measured as a function of temperature and salt concentration in the presence and absence of ATPgammaS, a specific ligand for TyrR. Fluorescence titrations yielded a KL value of 1.20 x 10(7) M-1 at 20 degrees C, which was independent of the acceptor (9F30A/30B) concentration in the range 5-500 nM, indicating that the system exhibits true equilibrium binding. Clarke and Glew analysis of the temperature dependence of binding revealed a linear dependence of R ln KL on temperature in the absence of ATPgammaS. The thermodynamic parameters obtained at 20 degrees C (theta) were = -35.73 kJ mol-1, = 57.41 kJ mol-1, and = 93.14 kJ mol-1. Saturating levels of ATPgammaS (200 microM) strengthened binding at all temperatures and resulted in a nonlinear dependence of Rln KL on temperature. The thermodynamic parameters characterizing binding under these conditions were = -39.32 kJ mol-1, = 37.16 kJ mol-1, = 76.40 kJ mol-1, and = -1.03 kJ mol-1 K-1. Several conclusions were drawn from these data. First, binding is entropically driven at 20 degrees C in both the presence and absence of ATPgammaS. This can partly be accounted for by counterions released from the DNA upon TyrR binding; in the absence of ATPgammaS and divalent cations, the TyrR-9F30A/30B interaction results in the release of two to three potassium ions. Second, the more favorable value, and hence tighter binding observed in the presence of ATPgammaS, is primarily due to a decrease in (-20.3 kJ mol-1), which overcomes an unfavorable decrease in (-16.7 kJ mol-1). Third, the negative value obtained in the presence of ATPgammaS indicates that the binding of ATPgammaS favors a conformational change in TyrR upon binding to 9F30A/30B, yielding a more stable complex.

Cations, Monovalent↗
PubMed1998

Randomized trial of the effect of supplementation on the cognitive function of older people with subnormal cobalamin levels.

BACKGROUND: Low serum cobalamin levels are often found in apparently normal older subjects. A major worry of leaving cobalamin deficiency untreated is that it may lead to subtle deterioration in cognitive function. OBJECTIVES: To investigate the effect of supplementation on the cognitive function of older people with cobalamin deficiency by a randomized trial. METHODS: Fifty Chinese subjects more than 60 years old with serum cobalamin level < 120 pmol/l were randomized into supplement and control groups. Fasting serum methylmalonic acid levels (MMA) were measured. A battery of neuropsychological tests was administered. The supplement group received intramuscular cyanocobalamin injections, while the control group received no intervention. They were followed up at around 4 months. RESULTS: 78% of the subjects had raised MMA, indicating metabolic cobalamin deficiency. Supplemented subjects improved in performance IQ, but the amount of improvement was not significantly more than that of control subjects. Moreover, the supplement group fared worse than the control group at follow-up in some motor function scores. Three out of seven demented subjects had improvement in Mini-Mental State Examination scores, but there was no consistent improvement in other neuropsychological scores. CONCLUSIONS: This study suggested that cobalamin deficiency did not invariably cause cognitive impairment in older people. There remain the possibilities that cobalamin deficiency causes cognitive impairment or exacerbates coexisting dementia in some older people.

Aged↗
PubMed1998

Rarity of debrisoquine hydroxylase gene polymorphism in Chinese patients with Parkinson's disease.

Impaired debrisoquine metabolism resulting from defects in the cytochrome P450 CYP2D6-debrisoquine hydroxylase gene has been shown to be associated with the development of Parkinson's disease (PD). We studied two polymorphisms in this gene in 207 Chinese PD patients and 227 control subjects by polymerase chain reaction and restriction analysis. The G to A substitution at position 1934 in the junction of intron 3/exon 4 was detected in one sporadic PD patient and two control subjects, all of whom were heterozygous. The single base deletion at position 2637 in exon 5 was not detected in any of the study subjects. Such rarity of CYP2D6 polymorphism indicates PD in the Chinese population is associated with some other gene defects.

Aged↗
PubMed1998

Bone mineral density in Chinese elderly female vegetarians, vegans, lacto-vegetarians and omnivores.

OBJECTIVES: To compare the bone mineral density and dietary intake of elderly Chinese vegetarian women with omnivores, to compare the bone mineral density of Chinese 'vegans' and 'lactovegetarians', and to study the relationship between nutrient intake and BMD in vegetarians. DESIGN: A cross-sectional survey. SETTING AND SUBJECTS: A community-based study. The vegetarian women (aged 70-89 y) (n = 76) were non-institutionalized subjects. All of them were Buddhists. Their bone mineral density were compared to normal elderly volunteers (aged 70-89 y) (n = 109) who were recruited to establish normal BMD ranges. Their dietary intake was compared to omnivorous subjects from a previous dietary survey (n = 250). METHODS: Dietary assessment was by the 24 h recall method, and bone mineral density was measured by dual-X-ray-densitometry. The analysis of co-variance was used to compare the BMD between vegetarians and omnivores, with adjustment for potential confounders. The BMD in 'vegans' and 'lactovegetarians' were compared by similar methods. The t-test was used to compare dietary intake between omnivores and vegetarians. The relationship between nutrient intake and BMD was studied by correlation and multiple regression. RESULTS: The dietary calorie, protein and fat intake were much lower, but the sodium/creatinine ratio was much higher in vegetarians than omnivores. The BMD at the spine was similar between vegetarians and omnivores. However, the BMD at the hip was significantly lower in vegetarians at some sites (P < 0.05). There was no significant difference in BMD between 'vegans' and 'lactovegetarians'. BMD in vegetarians appeared to be positively correlated with energy, protein and calcium intake; and negatively associated with urinary sodium/creatinine levels. CONCLUSIONS: There is a relationship between diet and BMD. The BMD at the hip was lower in vegetarians than omnivores, but no difference was observed between 'vegans' and 'lactovegetarians'. There is a complex relationship between the intake of various nutrient and BMD in vegetarians.

Aged↗
PubMed1998

Nutritional status of elderly Chinese vegetarians.

AIM: To study the nutritional status of elderly Chinese vegetarians. SUBJECTS AND METHOD: Dietary intake (using the 24-h recall method), anthropometric indices and some nutritional laboratory parameters were studied in 131 elderly Chinese vegetarian women with a mean age of 81 years. Data from age- and sex-matched omnivore subjects from previous elderly surveys were used for comparison. RESULTS: Total energy, fat and protein calorie, thiamine, riboflavin and niacin intakes were lower in vegetarians than in non-vegetarians, while carbohydrate calorie, calcium, potassium, retinol equivalent and ascorbic acid intakes were higher. The 25th, 50th and 75th percentile for total body fat were lower and those for corrected arm muscle area were higher in vegetarians. Both urinary Na/Cr and K/Cr ratios were higher but the Na/K ratio was similar to that in non-vegetarians, as were mean systolic and diastolic blood pressures. Serum total cholesterol was lower, while serum triglyceride concentration was similar. The mean haemoglobin level was lower in vegetarians, the prevalence of anaemia being 30%, with deficiencies in B12 and/or iron accounting for 64% of the anaemia, compared with only 30% in non-vegetarians. Serum B12 concentration below the reference range occurred in 54% of the vegetarian subjects. Vegetarians also had a lower prevalence of a history of ischaemic heart disease; however, the prevalence of smoking was also lower. CONCLUSION: While the Chinese vegetarian diet may result in a favourable risk-factor profile for ischaemic heart disease, it is deficient in many B vitamins and gives rise to a high frequency of nutritional anaemias.

Aged↗
PubMed1998

Genetic and environmental risk factors for Parkinson's disease in a Chinese population.

An epidemiological study of the environmental and genetic factors as well as the possible interplay between them was conducted among 215 patients with Parkinson's disease and 313 controls in a Chinese population in Hong Kong. In univariate analysis, a regular tea drinking habit was found to be a protective factor, which had not been reported before. Smoking (a protective factor), family history, duration of pesticide exposure (in years) in farming and pesticide exposure during farming in women (both risk factors) have been reported previously. In multivariate analysis, current smoking reached borderline significance at the 5% level and the variables, years exposed to pesticides and family history were significant at the 10% level. By contrast with the common occurrence of polymorphism of the CYP2D6 gene (a gene involved with xenobiotic metabolism) in white people, it is very rare in China and is not thought to be a significant factor contributing to Parkinson's disease in Chinese people.

Aged↗
PubMed1997

The reliability of upper limb anthropometry in older Chinese people.

OBJECTIVE: To evaluate the validity of the Durnin-Womersley equations and to derive our local predictive equations for body fat from upper limb skinfold thicknesses in older Chinese people in Hong Kong. To evaluate the validity of mid-arm circumference and corrected arm muscle area in predicting lean tissue mass in the same population. DESIGN: Comparison of fat percentages predicted by Durnin-Womersley (D-W) equations with those estimated by Dual energy X ray absorptiometry (DXA). Predictive equations derived from regression between upper limb skinfold thicknesses and fat percentages estimated by DXA were similarly evaluated in internal and external validation groups. Mid-arm circumference (MAC) and corrected arm muscle area (CAMA) were correlated with the limb lean tissue mass, body lean tissue mass and fat percentage. SUBJECTS: 354 female and 263 male, apparently well, community dwelling subjects, aged 69-82 y; of which 40 subjects of each sex were randomly selected from the study population for internal validation of the local predictive equations; 60 female and 33 male hospital medical outpatients, aged 61-87 y, were recruited for external validation. MEASUREMENTS: Triceps and biceps skinfold thicknesses, mid-arm circumference, body mass index, fat percentages, limb and whole body lean tissue masses estimated by Hologic QDR-2000 bone densitometer. RESULTS: Fat percentages calculated by D-W equations were significantly different from those estimated by DXA (average difference -2.4 (s.d. 4.8)% and +2.1 (5.2)% in females and males respectively). The corresponding differences for our local predictive equations were not significant (-0.9 (4.7)% and -0.5 (5.0)% in females and males respectively). There was a trend of under-estimation of body fat with increasing fatness. In the hospital medical outpatients, there was a significant difference between fat percentages predicted by our equation and those by DXA in female (-2.9(5.3)%), but not in male (+0.3(4.3)%) subjects. In males, MAC correlated with limb and body lean tissue masses as well as with fat percentage (r = 0.60, 0.68, 0.65 respectively). CAMA correlated similarly well with lean tissue masses but was more independent of fat percentage (r = 0.61, 0.65, 0.44 respectively). In females, both MAC and CAMA correlated poorly with limb and body lean tissue masses. Moreover, MAC correlated well with fat percentage (r = 0.80). CONCLUSION: Upper limb skinfold thicknesses measurement is a valid means of predicting body fat in older Chinese people. Local predictive equations were more reliable that D-W equations. They were, however, subject to errors at the extreme ends of body fatness and in the presence of disease. In older females, MAC and CAMA were not reliable in predicting lean tissue mass, but MAC could be used to predict fat percentages. In older males, CAMA was more reliable than MAC in predicting lean tissue mass.

Absorptiometry, Photon↗
PubMed1996

Apolipoprotein E genotype and Alzheimer's disease in Hong Kong elderly Chinese.

We studied the apolipoprotein E (apoE) allele frequencies in 65 Chinese patients with late-onset Alzheimer's disease (AD) and 82 age- and sex-matched controls. The apoE epsilon 4 allele frequency was significantly higher in the AD group than in the control group (0.169 versus, p < 0.01). There were five homozygotes for epsilon 4 in the AD group but none among the controls. The odds ratio for AD was 1.6 for epsilon 4 heterozygotes. The age at onset was lower in the presence of the epsilon 4 allele and higher with the epsilon 2 allele, although neither of these differences reached statistical significance. The association between apoE alleles and AD previously reported in Caucasian populations was also present in this reports of lower prevalence of AD compared with the prevalence of multi-infarct dementia.

Aged↗
PubMed1995

Analysis of an Escherichia coli mutant TyrR protein with impaired capacity for tyrosine-mediated repression, but still able to activate at sigma 70 promoters.

In Escherichia coli, TyrR represses and activates transcription of operons required for tyrosine, phenylalanine and tryptophan biosynthesis and uptake. The TyrR central domain is homologous with NtrC and some other bacterial regulatory proteins, although TyrR regulates sigma 70, not sigma 54, promoters. We isolated a central domain TyrR mutant (TyrR E274Q) by substitution of a normally conserved amino acid. The mutant was unable to bring about tyrosine-mediated repression of aroF, aroL, tyrB, and tyrP and had diminished capability for tyrosine- and phenylalanine-mediated repression of aroP. In contrast, it was able to effect wild-type levels of phenylalanine-mediated repression of aroG, tryptophan-mediated repression of aroP and transcriptional activation of mtr and tyrP. The binding of purified TyrR E274Q to ATP (a requirement for tyrosine binding) and to the strong TyrR box of tyrP operator DNA were normal, but tyrosine binding and tyrosine-dependent hexamerization were significantly impaired. These properties are consistent with the proposal that self association is essential for tyrosine-mediated repression by TyrR but not for tyrosine- or phenylalanine-mediated activation. E274 of TyrR must participate in either the binding of tyrosine, or the coupling of ATP binding with a conformational change that alters the affinity of the ATP-dependent aromatic amino acid-binding site.

Adenosine Triphosphatases↗
PubMed1994

Can topical zinc accentuate tuberculin reactivity in the elderly?

We examined the effect of topical zinc on Heaf tests in 58 elderly hospitalized patients in a double-blind study. Plasma zinc levels were measured. Thirty-eight subjects (66%) had negative reactions with placebo ointment. Fourteen of these negative responders (37%) had positive reactions with topical zinc ointment; 12 (32%) had weakly positive reactions and 12 remained negative. There was no significant difference in the plasma zinc levels between the different grades of topical zinc effect in the negative responders. Zinc deficiency is therefore unlikely to account for the observed booster effect of topical zinc on tuberculin reactivity.

Administration, Topical↗
PubMed1992

Thiamine status of elderly patients with cardiac failure.

This study compared the thiamine status of 37 elderly patients admitted with cardiac failure (CF) with that of 35 unselected elderly patients with other diagnoses (Non-CF), and with that of 41 apparently healthy elderly people. The thiamine pyrophosphate effect (TPPE) on erythrocyte transketolase activity was used to estimate thiamine status. The prevalence of thiamine deficiency (TPPE greater than 19%) on admission in the CF and Non-CF groups was 13% and 29%, respectively. The TPPE of the CF group was significantly lower than that of the Non-CF group, and was not significantly different from that of the elderly control group. The results indicate that thiamine deficiency is not common in an unselected group of elderly inpatients with cardiac failure, but a potential benefit of thiamine supplementation in such patients cannot be ruled out.

Adult↗
PubMed1991

The use of armspan in nutritional assessment of the elderly.

The use of body mass index (BMI) in the elderly is limited by the measurement of height which is often unreliable. Armspan approximates to height at maturity. It may, therefore, be an alternative to height in calculating BMI. We studied the relationship between height and armspan in 101 elderly men and women. A comparison of BMI by height and armspan was made. The correlation between height and armspan was 0.93. Armspan could be estimated by doubling halfspan (recumbent). The mean difference between BMI by height and armspan was 1.79 (SD 1.11) kg/M2. We concluded that armspan is a reliable and practical estimate of height in the non-ambulant elderly. There is a case for the use of armspan instead of height in the determination of BMI in the elderly.

Adult↗