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R W Taylor

Publications and source records attributed to R W Taylor.

At least 109 records · Page 6Linked to original sources
PubMed1996

Variant sequences of the Hexokinase II gene in familial NIDDM.

UNLABELLED: Hexokinase II (HKII) plays a central role in the intracellular metabolism of glucose in skeletal muscle, catalysing the phosphorylation of glucose to glucose 6-phosphate. It is therefore considered to be a potentially important candidate gene in the development of insulin resistance and non-insulin-dependent diabetes mellitus (NIDDM). The aim of this study was to screen the HKII gene for mutations in NIDDM subjects from insulin-resistant families. Insulin sensitivity was assessed in unaffected first degree relatives from families with two or more living NIDDM subjects, and 15 families were identified as being insulin resistant. In 15 NIDDM subjects (one from each family) and 4 normoglycaemic control subjects, all 18 exons of the HKII gene were amplified by the polymerase chain reaction, and the products screened for mutations using a combination of single-stranded conformational polymorphism analysis and direct sequencing. Six sequence variations were detected in the NIDDM subjects; four silent polymorphisms [GAT vs GAC at codon 251 in exon 7, AAT vs AAC at codon 692 in exon 15, CCG vs CCC at codon 736 in exon 15, and CTG vs CTA at codon 766 in exon 16]; a single base change [T-->C], 22 base pairs distal to the exon-intron junction of exon 17 in the 5'-splice donor; and a single amino acid substitution [Gln142-->His] in exon 4, which was identified in 6 of the 15 NIDDM subjects. The frequency of the mutated codon 142 allele however, was comparable between NIDDM subjects with familial NIDDM (n = 56) and normoglycaemic control subjects (n = 48) (18.8% and 14.6% for NIDDM subjects and control subjects respectively; chi 2 = 0.6, p > 0.25). In addition, measures of insulin sensitivity were comparable in normal glucose tolerant subjects with (n = 20) and without (n = 40) the codon 142 polymorphism. IN CONCLUSION: (1) mutations in the coding regions of the HKII gene are unlikely to be major determinants in the development of insulin resistance and familial NIDDM; although (2) the influence of the codon 142 mutation in combination with other abnormalities of the insulin-signalling pathway on insulin action remain to be addressed.

Amino Acid Sequence↗
PubMed1996

Genomic dispersion of 28S rDNA during karyotypic evolution in the ant genus Myrmecia (Formicidae)

The chromosomal localization of 28S rDNA was investigated in 16 speices of the Australian ant genus Myrmecia, with 2n numbers ranging from 4 to 76, using the fluorescence in situ hybridization method and karyographic analysis. A unique phenomenon was observed: the number of chromosomes carrying 28S rDNA increases from 2 in species with low chromosome numbers to 19 in species with high chromosome numbers. This is termed rDNA dispersion. Centric fission and a reciprocal translocation that occurs in C-bands were detected as the major mechanisms involved in rDNA dispersion.

Animals↗
PubMed1996

Regional body fat distribution in relation to pubertal stage: a dual-energy X-ray absorptiometry study of New Zealand girls and young women.

A cross-sectional study of 140 healthy, non-obese women and growing girls aged 8-27 y was undertaken to examine changes in total-body and regional fat and fat-free lean tissue mass by Tanner stage of pubertal development with dual-energy X-ray absorptiometry. Absolute fat mass and absolute fat-free lean tissue mass were higher at successive Tanner stages (1 through 5) but the proportional increase was greater for fat: total fat mass (kg) was about threefold higher in Tanner stage 5 than in stage 1 (P < 0.001), whereas lean tissue mass (kg) in Tanner stage 5 was about double that in stage 1 (P < 0.001). Furthermore, although the regional distribution of lean tissue mass in the trunk and legs remained fairly constant at different pubertal stages, the regional distribution of fat was altered significantly, becoming more central and less peripheral. Trunk fat (as a percentage of total body fat) was significantly higher at stage 5 than at stage 1 (P < 0.001). In the whole population, body mass index was positively correlated with trunk fat (r = 0.662, P < 0.0001) and negatively with leg fat (r = -0.457, P < 0.0001). We conclude that girls accumulate a higher proportion of their total adult fat mass than of their total adult lean tissue mass during puberty, and that regional fat patterns become more android and less gynoid with maturity.

Absorptiometry, Photon↗
PubMed1996

Regional body fat distribution in New Zealand girls aged 4-16 years: a cross-sectional study by dual energy X-ray absorptiometry.

OBJECTIVE: To measure total body fat content and its regional distribution within the body (head, arms, legs and trunk) in young girls and adolescents in relation to age and body mass index (BMI). DESIGN: Cross-sectional observational study. SUBJECTS: 196 healthy Caucasian girls aged 4-16 years living in an urban town in the South Island of New Zealand. MEASUREMENTS: Body weight, height and BMI. Total body fat mass (kg) and the regional distribution of this fat (measured by dual energy X-ray absorptiometry). RESULTS: All the measured variables, including total and % fat mass were higher in older age groups. Regional distribution of fat differed, with older girls having a higher proportion of their body fat in the trunk and a smaller proportion of their body fat in the heat than younger girls. BMI was positively correlated with % trunk fat (r = 0.700) and negatively correlated with % leg fat (r = -0.465). Girls with higher levels of adiposity (> 75th percentile for BMI) stored more fat in the trunk and correspondingly less in the legs than girls with lower adiposity (< or = 75th percentile for BMI) at five of the six age groups (P < 0.05). CONCLUSION: It is concluded that body fat mass increases and shows a more central distribution in young girls as they grow older. Increasing adiposity as determined by BMI is associated with an increase in fat deposition in the trunk and a decrease in the legs.

Absorptiometry, Photon↗
PubMed1996

DEXA supports the use of BMI as a measure of fatness in young girls.

OBJECTIVE: To examine the relationship of body fat mass measured by dual energy X-ray absorptiometry (DEXA) to BMI in young girls, according to age and normative BMI percentile groupings. DESIGN: Cross-sectional observation study. SETTING: Dunedin, an urban town in the South Island of New Zealand. SUBJECTS: 196 healthy Caucasian girls aged 4-16 y. MEASUREMENTS: Body weight, height and BMI, total fat mass and % body fat (by DEXA). RESULTS: Our BMI percentile standard groupings were < 5 centile (n = 7); 5-50 centile (n = 71); 51-75 centile (n = 50); 76-90 centile (n = 42); 91-95 centile (n = 12); > 95 centile (n = 14). In this whole population sample DEXA-derived fat mass correlates well with BMI (n = 0.934) indicating that BMI accounts for 87.2% of the variance in body fat mass. However, at the extremes of BMI the association is weaker. A nomogram for predicting DEXA fat mass from BMI in girls is presented. CONCLUSION: Because DEXA-derived fat mass correlates well with BMI throughout the 'normal' range of BMI (5-95th centiles) our study supports the usefulness of BMI as a simple measure of fatness in girls. Children with BMI values outside the normal BMI range may benefit from more exact body composition assessment using DEXA.

Absorptiometry, Photon↗
PubMed1995

Mitochondrial-DNA sequence evidence on the phylogeny of Australian jack-jumper ants of the Myrmecia pilosula complex.

Australian ants of the Myrmecia pilosula species complex include some individuals (in M. croslandi) with the lowest possible metazoan chromosome number of 2n = 2. Others in this cluster of sibling species have much higher numbers, the known maximum being 2n = 32. Two species (M. pilosula and M. 'banksi') are believed on cytogenetic and morphological grounds to have hybridized over a long period. To investigate the phylogeny and age of this group relative to the congeneric outgroup species M. gulosa, we sequenced part of the cytochrome b gene and the intergenic sequence between it and a primer anchored on the nearby tRNA(UCNSer) gene and analyzed the coding region using bootstrapped parsimony and neighbor-joining trees using the numbers of synonymous and nonsynonymous codons per site. The intergenic space demonstrated a profusion of repeated sequences, and only very closely related sequences (as judged by that for cytochrome b) showed detectable similarity at this almost 100% A+T region. In agreement with predictions from karyotype studies, the phylogenetic analyses showed that M. croslandi is the sister group to the other siblings; the time of separation of M. croslandi from the rest of the pilosula group is unexpectedly ancient. Other relationships were poorly resolved, but the results suggest that M. 'banski' and M. pilosula cluster together, as expected on cytogenetic grounds, and the tentative suggestion of close affinity of the M. pilosula samples and two "PB" samples supports derivation of PB from female M. pilosula and male M. 'banksi.'

Animals↗
PubMed1995

Neonatal Fanconi syndrome due to deficiency of complex III of the respiratory chain.

Fanconi syndrome is an important presentation of respiratory chain disease. We report three patients who presented in the neonatal period with Fanconi syndrome, lactic acidosis and intrauterine growth retardation. In all three patients the major biochemical defect was in complex III of the mitochondrial respiratory chain, a relatively uncommon defect. The diagnosis could only be made by muscle biopsy as the defect was not expressed in cultured skin fibroblasts. Treatment with vitamins C and K3 and ubiquinone did not alter the course of the disease and all patients died before the age of 4 months.

Acidosis, Lactic↗
PubMed1995

Effects of pH conditions on Ca2+ transport catalyzed by ionophores A23187, 4-BrA23187, and ionomycin suggest problems with common applications of these compounds in biological systems.

Phospholipid vesicles loaded with Quin-2 and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) have been used to investigate the effects of pH conditions on Ca2+ transport catalyzed by ionophores A23187, 4-BrA23187, and ionomycin. At an external pH of 7.0, a delta pH (inside basic) of 0.4-0.6 U decreases the rate of Ca2+ transport into the vesicles by severalfold under some conditions. The apparent extent of transport is also decreased. In contrast, raising the pH by 0.4-0.6 U in the absence of a delta pH increases both of these parameters, although by smaller factors. The relatively large effects of a delta pH on the transport properties of Ca2+ ionophores seem to reflect a partial equilibration of the transmembrane ionophore distribution with the H+ concentration gradient across the vesicle membrane. This unequal distribution of ionophore can cause a very slow or incomplete ionophore-dependent equilibration of delta pCa with delta pH. A second factor of less certain origin retards full equilibration of delta pCa when delta pH = 0. These findings call into question several ionophore-based methods that are used to investigate the regulatory activities of Ca2+ and other divalent cations in biological systems. Notable among these are the null-point titration method for determining the concentration of free cations within cells and the use of ionophores plus external cation buffers to calibrate intracellular cation indicators. The present findings also indicate that the transport mode of Ca2+ ionophores is more strictly electroneutral than was thought, based upon previous studies.

Aminoquinolines↗
PubMed1995

Rhabdomyolysis and acute encephalopathy in late onset medium chain acyl-CoA dehydrogenase deficiency.

A previously asymptomatic 30 year old man presented with rhabdomyolysis, muscle weakness, and acute encephalopathy after strenuous exertion in the cold without adequate food intake. Serum and muscle carnitine concentrations were decreased. Urinary excretion of carnitine and glycine esters and biochemical examination of skeletal muscle and fibroblasts led to the diagnosis of medium chain acyl-CoA dehydrogenase (MCAD) deficiency. A point mutation at nucleotide position 985 of the coding region of the MCAD gene was found. The MCAD protein was synthesised in the patient's fibroblasts at a normal rate, but was unstable. In general, patients in whom the 985 point mutation has been established show much more severe clinical symptoms and other symptoms than those seen in this patient. The relation of the 985 point mutation and the residual MACD activity to the symptoms is not as straightforward as previously thought.

Acyl-CoA Dehydrogenase↗
PubMed1994

The control of mitochondrial oxidations by complex III in rat muscle and liver mitochondria. Implications for our understanding of mitochondrial cytopathies in man.

We have studied the control by complex III of both succinate-cytochrome c reductase and of oxidative flux measured polarographically in rat muscle and liver mitochondria using the specific inhibitor, myxothiazol, to induce partial inhibitions of complex III activity. Complex III exerted a low degree of control on electron flux through succinate-cytochrome c reductase, and a 30-50% decrease in complex III activity remained undetected by this assay. However, when overall oxidative flux was measured polarographically there was a considerable difference in the effect of lowered complex III activity on this pathway between rat muscle and liver mitochondria. Small changes in complex III activity (approximately 5% inhibition) in muscle mitochondria caused marked changes in succinate-stimulated respiration, whereas in liver mitochondria complex III had to be inhibited by about 45% before changes in maximum oxidation rates could be detected. These differences between muscle and liver mitochondria occurred despite rat liver mitochondria having at least a 4-fold lower complex III activity. This suggests that when considering the biochemical consequences of defects of the respiratory chain an important factor is the degree to which an individual complex can be lowered before major changes in overall flux occur. In addition, since many patients with respiratory chain disease present with predominantly muscle symptoms, this latter finding suggests that an understanding of the control of mitochondrial oxidations by different tissues may be important when considering the tissue-specific nature of defects of the respiratory chain.

Animals↗
PubMed1994

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex.

Chromosomal localization of rDNA in samples of five taxa of the Mymecia pilosula species complex (Hymenoptera: Formicidae: Myrmeciinae) with 2n = 3 (M. croslandi), 8 (M. imaii), 10 (M. banksi), 18 (M. haskinsorum), and 27 (M. pilosula) was carried out by fluorescence in situ hybridization (FISH) using cloned M. croslandi rDNA (pMc.r2) including the coding region for 28S rRNA. Results show that (1) the 28S rDNA in the genome of these ants is repetitive and is localized in pericentromeric C-bands, (2) the number of chromosomes carrying rDNA is two in M. croslandi, M. imaii and M. banksi, six in M. haskinsorum and ten in M. pilosula, and (3) only one or two clusters of rRNA genes generate nucleoli in each species. We suggest that the rDNA in the ancestral stock of the M. pilosula complex was localized originally in a pericentromeric C-band, and multiplied by chance with time during saltatory increases in C-banding following episodes of centric fission. Most rDNA multiplied on various chromosomes seems to be inactivated and eliminated from the genome, together with C-bands, by AM-inversion or centric fusion, with the remnant rDNAs dispersed in the genome by centric fission and AM-inversion.

Animals↗
PubMed1994

Ca2+ transport properties of ionophores A23187, ionomycin, and 4-BrA23187 in a well defined model system.

Models for the electroneutral transport of Ca2+ by ionophores A23187, ionomycin, and 4-BrA23187 have been tested in a defined system comprised of 1-palmitoyl-2-oleoyl-sn-glycerophosphatidylcholine vesicles prepared by freeze-thaw extrusion. Quin-2-loaded and CaCl2-loaded vesicles were employed to allow the investigation of transport in both directions. Simultaneous or parallel measurements of H+ transport and membrane potential, respectively, indicate that for any of these ionophores, electrogenic transport events do not exceed 1 in 10,000 when there is no preexisting transmembrane potential. When a potential of approximately 150 mV is imposed across the membrane, transport catalyzed by A23187 remains electroneutral; however, for ionomycin and 4-BrA23187, approximately 10% of transport events may be electrogenic. The defined vesicle system has also been utilized to determine how the rate of Ca2+ transport varies as a function of ionophore and Ca2+ concentration and with the direction of transport. Some aspects of the results are unexpected and should be considered by investigators using ionophores in biological systems. These include the apparent failure of these compounds to fully equilibrate Ca2+ with a high affinity Ca2+ indicator when these species are separated by a membrane, rates of transport that vary markedly with the direction of transport, and extents of transport that are a function of ionophore concentration. At least some of these unexpected behaviors can be explained by a strong influence of delta pH on forward and reverse transport kinetics. In the case of A23187, the data also give some initial insights into the relationship between formation of the transporting species and the entry of this species into the membrane hydrophobic region.

Biophysical Phenomena↗
PubMed1993

Succinate-cytochrome c reductase: assessment of its value in the investigation of defects of the respiratory chain.

Defects of the respiratory chain are important causes of human disease and one of the most commonly used assays in the investigation of these patients is the measurement of succinate-cytochrome c reductase. However, this assay measures several components of the respiratory chain and the ability to detect a partial defect in one enzyme complex will depend on the amount of control exerted by that enzyme step on overall electron flux. We show that measurement of succinate-cytochrome c reductase activity may fail to detect partial defects of complex III and therefore is of limited diagnostic value in the identification of complex III defects. However, complex II is a major point of control of flux through succinate-cytochrome reductase and it is likely that measurement of the latter will detect defects of complex II.

Animals↗