PubMed Health⌕ Search

Biomedical subjects

K W Wang

Publications and source records attributed to K W Wang.

At least 19 recordsLinked to original sources
PubMed2004

An enzymatic route to produce pyruvate from lactate.

A bacterial strain of Acinetobacter sp., which was capable of enzymatic production of pyruvate from lactate, was cultured in a 5-l reactor with a basal salt medium. After 14 h of fed-batch fermentation, 9.56 g l(-1) cell concentration in the broth was obtained with 20 g l(-1) (178 mM) sodium lactate and 4 g l(-1) NH(4)Cl in the medium; and the biotransformation ability was 2.51 units ml(-1). The cells were harvested from one reactor and then used for pyruvate production from lactate in the same reactor. l-lactate at a concentration about 527 mM was almost stoichiometrically converted to pyruvate in 28 h. After a total 42 h of cell culture and biotransformation, the transformative yield was about 0.72 g g(-1) pyruvate from lactate and the rate of pyruvate production was calculated as 1.33 g l(-1) h(-1) during the process. The results suggested this simple enzymatic production of pyruvate from lactate should be a promising process and may bring a yield higher than that by microbial fermentation. By this process, the recovery of pyruvate from such a simple reaction liquid is relatively easy and inexpensive to perform.

Acinetobacter↗
PubMed1998

Sequence and function of the two P domain potassium channels: implications of an emerging superfamily.

A new superfamily of K+ channels has emerged in the past 2 years. Notable for possessing two pore-forming P domains in each subunit, members of the superfamily have been recognized through phylogeny from micro-organisms to humans. Four subfamilies of two P domain channels have been isolated thus far; among these are the first cloned examples of outward rectifier and open rectifier (or leak) K+ channels. The two P domain K+ channels offer a new perspective from which to glimpse the molecular basis for function and dysfunction of K+-selective ion channels.

Amino Acid Sequence↗
PubMed1997

A minK-HERG complex regulates the cardiac potassium current I(Kr).

MinK is a widely expressed protein of relative molecular mass approximately 15K that forms potassium channels by aggregation with other membrane proteins. MinK governs ion channel activation, regulation by second messengers, and the function and structure of the ion conduction pathway. Association of minK with a channel protein known as KvLQT1 produces a voltage-gated outward K+ current (I[sK]) resembling the slow cardiac repolarization current (I[Ks]). HERG, a human homologue of the ether-a-go-go gene of the fruitfly Drosophila melanogaster, encodes a protein that produces the rapidly activating cardiac delayed rectifier (I[Kr]). These two potassium currents, I(Ks) and I(Kr), provide the principal repolarizing currents in cardiac myocytes for the termination of action potentials. Although heterologously expressed HERG channels are largely indistinguishable from native cardiac I(Kr), a role for minK in this current is suggested by the diminished I(Kr) in an atrial tumour line subjected to minK antisense suppression. Here we show that HERG and minK form a stable complex, and that this heteromultimerization regulates I(Kr) activity. MinK, through the formation of heteromeric channel complexes, is thus central to the control of the heart rate and rhythm.

Animals↗
PubMed1997

MinK potassium channels are heteromultimeric complexes.

MinK is a transmembrane protein of 130 amino acids found in the kidney, heart, and vestibular system of mammals. Its expression in Xenopus laevis oocytes induces a voltage-dependent potassium current similar to that seen in vivo. Indirect evidence has fueled speculation that function requires association of MinK and another protein endogenous to oocytes and native tissues. In this report, we show that direct covalent modification of an oocyte membrane protein alters properties of the MinK ion conduction pore; modified channels exhibit decreased potassium conduction and increased permeability to sodium and cesium. The modifying reagents, two membrane-impermeant, sulfhydryl-specific methanethiosulfonate derivatives, react only from the extracellular solution at rates that are determined by the conformational state of the channel. These findings indicate that MinK is intimately associated with an oocyte protein whose exposure to the external solution changes during channel gating and which acts with MinK to establish ion conduction pore function.

Animals↗
PubMed1996

Biodegradation of mixed wastes in continuously operated cyclic reactors.

The problem of simultaneous biodegradation of two dissimilar substrates in a continuously operated cyclic reactor was studied both at the theoretical and experimental levels using a simple model system. The system involved media containing mixtures of glucose and phenol as carbon sources. A pure culture of Pseudomonas putida (ATCC 17514) was employed. Independent kinetic experiments have revealed that glucose and phenol are involved in a crossinhibitory uncompetitive kinetic interaction. The dynamics of a cyclically operated reactor were analyzed using the principles of bifurcation theory for forced systems. Experimental results have confirmed the theoretical predictions. Implications of the results for the design of waste-treating facilities are discussed.

Biodegradation, Environmental↗
PubMed1996

MinK residues line a potassium channel pore.

MinK has neither the P region nor signature sequence that characterizes pore-forming subunits of all known K+ channels. A specific minK region has now been identified that affects external blockade by 2 common probes of K+ channel pores. When mutated to cysteine, residues in this region render minK susceptible to covalent blockade by methanethiosulfonate ethylsulfonate and alter reversible inhibition by tetraethylammonium. The 2 blockers are found to share overlapping binding site determinants and to interact. Since inhibition by external tetraethylammonium is sensitive to voltage and to the internal concentration of permeant ions, we argue that tetraethylammonium blocks by occluding the external end of a water-filled transmembrane pore. These findings support the view that minK is directly involved in forming a K+-selective ion conduction pathway.

Molecular Structure↗
PubMed1995

Ion binding constants for gramicidin A obtained from water permeability measurements.

Gramicidin A pores are permeable to water and small monovalent cations. For K, Rb, and Cs there is good evidence from conductances and permeability ratios that a second ion can enter a pore already occupied by another, but for Na this evidence is inconclusive and comparison of tracer fluxes and single channel conductances suggests that second ion entries are prohibited. Partly as a result of the complications of second ion entry there have been widely differing estimates for the dissociation constants for the first ion in the channel. Dani and Levitt (1981, Biophys. J. 35: 485-499) introduced a method for calculating ion binding constants from simultaneous measurements of water fluxes and membrane conductance. They found no evidence for second ion binding and calculated dissociation constants of 115 mM for Li, 69 mM for K, and 2 mM for Tl. It is shown here that the two-ion, four-state model predicts a dependence of water permeability on ion concentration that is difficult to distinguish from the predictions of block by a single ion. Using a modified technique that allows measurement of higher conductances, the first ion dissociation constants have been determined as 80 mM for Na, 40 mM for Rb and 15 mM for Cs. These values and those of Dani and Levitt fall in a smooth sequence. The dissociation constant for Cs is consistent with single channel conductances and flux ratios. There is a discrepancy between this constant for Na and the value, 370 mM, calculated from the single channel conductances and the assumption that a second ion cannot enter or affect an occupied pore. The dissociation constant for Rb is intermediate between those for K and Cs whereas tracer flux measurements (Schagina, Grinfeldt & Lev, 1983. J. Membrane Biol. 73: 203-216) have suggested that Rb interacts much more strongly with the channel than Cs.

Animals↗
PubMed1995

Subunit composition of minK potassium channels.

Expression of minK protein in Xenopus oocytes induces a slowly activating, voltage-dependent, potassium-selective current. Point mutations in minK that alter current gating kinetics, ion selectivity, pharmacology, and response to protein kinase C all support the notion that minK is a structural protein for a channel-type transporter. Yet, minK has just 130 amino acids and a single transmembrane domain. Though larger cloned potassium channels form functional channels through tetrameric subunit association, the subunit composition of minK is unknown. Subunit stoichiometry was determined by coexpression of wild-type minK and a dominant lethal point mutant of minK, which reaches the plasma membrane but passes no current. The results support a model for complete minK potassium channels in which just two minK monomers are present, with other, as yet unidentified, non-minK subunits.

Animals↗
PubMed1994

An upper limit for the effect of low frequency magnetic fields on ATP-sensitive potassium channels.

Currents have been recorded for ATP-sensitive potassium channels in excised patches of membranes from an insulin secreting cell line, CRI-G1. The multi-channel records have been analyzed to reveal the single-channel conductance, the frequency and duration of bursts and the frequency of flickers (with periods between 0.5 and 5 ms). Control records in the absence of applied magnetic fields are similar to those reported by others. Patches have been exposed to parallel static and low frequency magnetic fields including a combination satisfying the 'cyclotron resonance' condition. The fields were applied for 30 s periods interleaved with 30 s controls. No significant differences in channel properties were observed between the control and field exposed periods. The largest change in position of the peak of the distribution of opening and closing transitions was 3%.

Adenosine Triphosphate↗
PubMed1994

The effect of a 5-month supervised program of physical activity on anthropometric indices, fat-free mass, and resting energy expenditure in obese male military recruits.

Studies using mainly dietary restriction have shown that weight loss is associated with a decrease in fat-free mass (FFM) and resting energy expenditure (REE). The aim of this study was to investigate the effects of a weight-loss program relying solely on increased physical activity on FFM and REE. Forty-two overweight male military recruits (12 with initial body mass index [BMI] between 25.0 and 29.9 kg/m2, group 1; 14 with BMI between 30.0 and 34.9 kg/m2, group 2; and 16 with BMI of at least 35 kg/m2, group 3) completed a 5-month program of supervised physical activity that included both aerobic and muscle-strengthening components. All subjects lost significant amounts of weight (group 1, 8.6 kg; group 2, 15.7 kg; group 3, 22.0 kg). This weight loss was accompanied by a significant reduction in the waist to hip ratio (WHR) in all groups. FFM was maintained in all groups. REE tended to decline in all groups (group 1, from 1,595.0 +/- 46.9 to 1,511.7 +/- 53.2 kcal/d; group 2, from 1,751.4 +/- 56.0 to 1,680.0 +/- 63.1 kcal/d; group 3, from 1,901.9 +/- 93.7 to 1,740.0 +/- 67.3 kcal/d), but this decline reached statistical significance only when all 42 subjects were considered. REE normalized for FFM did not decrease except in group 1. Furthermore, differences between the slopes and intercepts of the regression lines relating REE with FFM before and at completion of the 5-month program were not statistically significant, suggesting that the relationship between REE and FFM was maintained after weight loss.(ABSTRACT TRUNCATED AT 250 WORDS)

Anthropometry↗
PubMed1994

Absence of effects of low-frequency, low-amplitude magnetic fields on the properties of gramicidin A channels.

The effects of static and low-frequency magnetic fields on gramicidin A channels have been investigated using bilayer patch clamp recording and a bridge technique capable of detecting 0.3% changes in the conductance of glyceryl monooleate membranes containing many channels. In the bridge technique the conductance was assessed using 10-ms voltage pulses applied at 10 Hz. Measurements were made for LiCl, KCl, and CsCl using magnetic fields of 50, 100, 500, and 5000 microT with the frequency scanned from 10-200 Hz. The combinations of static and low-frequency fields employed include the "cyclotron resonance" conditions at which effects had been predicted to occur. In no case was there any detectable change in conductance when the magnetic fields were applied or changed. Potassium currents through single gramicidin channels have been recorded for patches in which several channels may be open at once. Fields were applied for 2 min periods interleaved with 2 min controls. Methods have been developed to analyze the multichannel records to reveal the amplitude and duration of the channels together with the frequency, depth, and apparent period of flickers. No significant differences were observed between the control and field-exposed recording periods. The peak of the distribution of opening and closing transitions always coincided for fields on and off within the resolution, 0.4%, of the recordings. There are at least two types of flicker, one with typical period less than 0.1 ms, the other with typical period from 0.3-0.8 ms. Most of the latter were not complete closures with the conductance during a flicker 15-20% above the level for a full closure.

Electric Conductivity↗
PubMed1994

Metabolic abnormalities in young non-obese males with hypertension.

Essential hypertension has been shown by various studies to be an insulin-resistant state. However, most of these studies have included obese and elderly patients. We were interested to know the extent of insulin resistance in a group of young, non-obese patients with hypertension. A total of 59 male patients with essential hypertension and 31 controls matched for age, sex and body mass index were studied. All the subjects were under 35 years old and had a body mass index of less than 27 kg/m2. Our results showed that such patients with hypertension had significantly higher fasting insulin, total insulin after glucose challenge, insulin/glucose ratio and higher triglycerides than the control subjects.

Adult↗
PubMed1992

Hyperinsulinaemia in non-obese subjects with hypertriglyceridaemia: a preliminary report.

It has been known for some time that hyperinsulinaemia is associated with hypertriglyceridaemia. However, previous studies looking at the relationship between hyperinsulinaemia and hypertriglyceridaemia have included overweight subjects. The effect of obesity on the insulin status of hypertriglyceridaemic patients is uncertain. We investigated the insulin status of hypertriglyceridaemic subjects in the absence of confounding factors such as obesity, hypertension and diabetes mellitus. Our results demonstrate that basal insulin levels as well as the insulin response after an intravenous glucose challenge are higher in moderately hypertriglyceridaemic patients when compared to age and body mass index matched controls. Hyperinsulinaemia may have pathogenetic significance for hypertriglyceridaemia as well as other features of a constellation of metabolic derangements such as obesity, hypertension and glucose intolerance.

Adult↗
PubMed1990

Cardiovascular diseases in Chinese, Malays, and Indians in Singapore. II. Differences in risk factor levels.

STUDY OBJECTIVE: The aim of the study was to examine cardiovascular risk factors to see how these might explain differences in cardiovascular disease mortality among Chinese, Malays, and Indians in the Republic of Singapore. DESIGN: The study was a population based cross sectional survey. Stratified systematic sampling of census districts, reticulated units, and houses was used. The proportions of Malay and Indian households were increased to improve statistical efficiency, since about 75% of the population is Chinese. SETTING: Subjects were recruited from all parts of the Republic of Singapore. SUBJECTS: 2143 subjects aged 18 to 69 years were recruited (representing 60.3% of persons approached). There were no differences in response rate between the sexes and ethnic groups. MEASUREMENTS AND MAIN RESULTS: Data on cardiovascular risk factors were collected by questionnaire. Measurements were made of blood pressure, serum cholesterol, low and high density lipoprotein cholesterol, fasting triglycerides and plasma glucose. In males the age adjusted cigarette smoking rate was higher in Malays (53.3%) than in Chinese (37.4%) or Indians (44.5%). In both sexes, Malays had higher age adjusted mean systolic blood pressure: males 124.6 mm Hg v 121.2 mm Hg (Chinese) and 121.2 mm Hg (Indians); females 122.8 mm Hg v 117.3 mm Hg (Chinese) and 118.4 mm Hg (Indians). Serum cholesterol, low density lipoprotein cholesterol and triglyceride showed no ethnic differences. Mean high density lipoprotein cholesterol in males (age adjusted) was lower in Indians (0.69 mmol/litre) than in Chinese (0.87 mmol/litre) and Malays (0.82 mmol/litre); in females the mean value of 0.95 mmol/litre in Indians was lower than in Chinese (1.05 mmol/litre) and Malays (1.03 mmol/litre). Rank prevalence of diabetes for males was Indians (highest), Malays and then Chinese; for females it was Malays, Indians, Chinese. CONCLUSIONS: The higher mortality from ischaemic heart disease found in Indians in Singapore cannot be explained by the major risk factors of cigarette smoking, blood pressure and serum cholesterol; lower high density lipoprotein cholesterol and higher rates of diabetes may be part of the explanation. The higher systolic blood pressures in Malays may explain their higher hypertensive disease mortality.

Adolescent↗
PubMed1990

Manifestations and outcome of treatment of thyrotoxicosis: a clinical study.

We studied a series of 89 consecutive patients who presented with thyrotoxicosis at a medical unit. Clinical parameters and laboratory abnormalities were recorded. Treatment was initiated and response in terms of side-effects, clinical and laboratory remissions were monitored. The frequency of the various clinical manifestations, cardiovascular and neurological complications were documented. Laboratory data on electrolytes, haematological changes and thyroid antibodies were noted. The treatment outcome revealed a relapse of 37.7% in patients with 6 months of treatment (90% occurred within the first year). We also noted that 6.7% of patients developed skin reaction. A treatment default rate of 30% was noted.

Adolescent↗
PubMed1990

Accelerated synthesis and release of angiotensin II in the rat brain during electroacupuncture tolerance.

Behavioural studies suggested that cerebral angiotensin II (AII) plays an important role in the development of tolerance to electroacupuncture (EA) analgesia. Observations made in this study revealed an increase in AII immunoreactivity (AII-ir) in both CSF and brain as well as an increase in the cerebral content of AI-ir in rats rendered tolerant to EA. The extracts of brain from rats receiving EA for 1h and 3h were subjected to gel filtration and the elution profile was compared with that of normal brain extract. There was a marked right shift of the AII peak from the large molecule precursor to the small molecule AII-ir. The latter peak showed the same retention time in HPLC system as that of AII. The results suggest that the acceleration of the synthesis and release of AII during a long-term EA stimulation might constitute one of the mechanisms for EA tolerance.

Acupuncture Analgesia↗