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Biomedical subjects

P M George

Publications and source records attributed to P M George.

At least 19 recordsLinked to original sources
PubMed1996

Yeast aspartic protease 3 (Yap3) prefers substrates with basic residues in the P2, P1 and P2' positions.

The yeast aspartic protease Yap3 is localised to the secretory pathway and correctly cleaves pro-alpha-mating factor at its dibasic sites. We determined the specificity of Yap3 for mono-, di-, and multi-basic cleavage sites in the context of 15 residue synthetic proalbumin peptides. Yap3 cleaved after dibasic ArgArg and LysArg sites but not after monobasic Arg sites even when there was an additional arginine at -6 and/or -4. Yap3 did not cleave a tetra-arginine site and tri-basic sites (RRR and RRK) were poor substrates. Cleavage always occurred C-terminal to the last arginine in the di- or tri-basic sequence. The optimal cleavage site sequence was RR DR and this substrate was cleaved 8-9-fold faster than the normal RR DA sequence. In contrast to Kex2, Yap3 did not remove the propeptide from normal proalbumin or a range of natural or recombinant proalbumin variants. However at pH 4.0 Yap3 slowly cleaved proalbumin and albumin between domains 2 and 3.

Amino Acid Sequence↗
PubMed1996

Expression of human Krev-1 gene in lungs of transgenic mice and subsequent reduction in multiplicity of ethyl carbamate-induced lung adenomas.

Mice of the A/J strain are useful models of lung cancer because they develop tumors spontaneously or after treatment with ethyl carbamate. These tumors are thought to arise from either Clara cells (papillary tumors) or alveolar type 2 cells (alveolar tumors); like many human lung adenocarcinomas, the mouse tumors involve Kiras activation. Transformation with Ki-ras can be reversed by coexpression of the Krev-1 gene in tissue culture. To test the tumor suppressor activity of Krev-1 in vivo, we produced transgenic A/J mice expressing Krev-1 under the control of the rabbit uteroglobin promoter, which directs expression of heterologous genes to the lung Clara cells. Krev-1 was expressed specifically in the lungs of transgenic mice. Sixty-six mice (35 transgenic and 31 nontransgenic) from three lines were given ethyl carbamate, and the numbers of resulting lung tumors were compared between transgenic and nontransgenic animals. The mean number (+/-standard deviation) of ethyl carbamate-induced lung tumors was 21.7 +/- 1.3 in transgenic mice and 26.9 +/- 1.3 in their nontransgenic littermates (P < 0.01). Sequencing of polymerase chain reaction-amplified ras DNA from 15 transgenic mouse tumors and 16 nontransgenic mouse tumors (controls) detected mutations in codon 61 in 13 tumors from the transgenic group and 11 tumors in the control group, whereas mutations in codon 12 were detected in only one tumor in the transgenic group and in four tumors in the controls. Together, these data demonstrate for the first time the tumor suppressor activity of Krev-1 in vivo and suggest that Krev-1 tumor suppressor activity may be specific for cells harboring mutations in codon 12 of ras.

Adenoma↗
PubMed1996

Trends in photoprotection in American fashion magazines, 1983-1993. will fashion make you look old and ugly?

BACKGROUND: During the past 50 years recreational sun exposure has greatly increased in the United States. OBJECTIVE: The purpose of this study was to examine the photoprotecion message of American fashion magazines and to identify recent trends. METHODS: We evaluated models for tan, skin exposure, and other sun-related criteria in six leading fashion magazines between 1983 and 1993. We also recorded the number of sunscreen advertisements and sun awareness articles. RESULTS: We evaluated 3031 models. Adult models had darker tans and greater skin exposure than adolescents and children. Men had darker tans than women. We noted trends toward lighter tans, more women wearing hats, more sunscreen advertisements, and sun awareness articles. Many sunscreen advertisements glorified tanning. Their models had darker tans and more skin exposure, and fewer wore a hat than did nonadvertisement models. CONCLUSION: The fashion industry and especially sunsreen manufacturers promote excessive sun exposure. Although we found encouraging trends, gains were modest, especially in men's magazines.

Adolescent↗
PubMed1996

Fibrinogen Lincoln: a new truncated alpha chain variant with delayed clotting.

A patient referred for preoperative investigation of prolonged bleeding and easy bruising was found to have increased thrombin and reptilase times; however, the thrombin catalysed release of fibrinopeptides A and B was normal. Analysis of five other family members, spanning three generations, indicated that three had a similar defect and suggested autosomal dominant inheritance. Non-reducing SDS-PAGE of purified fibrinogen from affected individuals showed that the 340 kD form of their fibrinogen ran as a doublet. SSCP (single-stranded conformational polymorphism) analysis of exon 5 of the A alpha gene, which encodes the C-terminal half of the chain, confirmed the presence of a mutation. Cycle sequencing of PCR amplified DNA revealed a 13 base pair deletion (nt 4758-4770), resulting in a frame-shift at Ala 475, which translates as four new amino acids before terminating at a new stop codon (-476His-Cys-Leu-Ala-Stop). The presence of a circulating truncated A alpha chain was confirmed when SDS-PAGE gels were probed with an alpha chain specific antisera; which showed that the variant A alpha chain comigrated with gamma chains. The truncation results in a variant A alpha chain with a deletion of 131 amino acids (480-610), and four new amino acids at the C-terminal.

Adult↗
PubMed1996

The specificity of the neuroendocrine convertase PC3 is determined by residues NH2- and COOH-terminal to the cleavage site.

The Kex2-like convertase PC3 (PC1) has been implicated in the processing of a number of prohormones and proneuropeptides. In order to be able to more accurately predict substrates for PC3 its specificity was defined using recombinant proalbumins and synthetic peptide substrates. P2P1 and P4P1 dibasic sites were cleaved with similar efficiencies however there were specific restrictions on amino acids NH2- and COOH-terminal to the cleavage site. His was disallowed at P2 and basic residues were forbidden at P1. The presence of a charged residue at P2 either completely prevented (Arg) or seriously impaired (Glu) cleavage by PC3 and the presence of a P4 Arg did not significantly increase its activity.

Amino Acid Sequence↗
PubMed1996

Comparison of histological and biochemical hepatic iron indexes in the diagnosis of genetic haemochromatosis.

AIMS: To compare a histological hepatic iron index with a biochemical hepatic iron index, derived from atomic absorption spectroscopy measurements of hepatic iron content, for the diagnosis of genetic haemochromatosis (GH). METHODS: Histological sections of liver biopsy specimens from 70 subjects, who had previously had their biochemical hepatic iron index measured, were examined. The iron stores were scored to derive a histological hepatic iron index and were also graded from 0 to 4 by a standard grading system. The case history of each patient was then reviewed to establish a definitive clinical diagnosis and patients were classified as GH, non-GH or indeterminate. RESULTS: There were 26 cases of GH, 40 cases of non-GH and four indeterminate cases in whom a definite clinical diagnosis was not established. Using a biochemical hepatic iron index cut off level of 2.0, two cases were misclassified, with one case of GH having a biochemical hepatic iron index of 1.8 and one non-GH case having a biochemical hepatic iron index of 3.1. This could not have been improved by altering the cut off level. Using the recommended cut off level of 0.15, the histological hepatic iron index was raised in all cases of GH, but was also increased in 11 of the 40 non-GH patients. The specificity of this histological index can be improved by increasing the cut off level to 0.30. A histological iron grade of > or = 3 is more specific than the histological index but has a lower sensitivity, which particularly affects the diagnosis of younger patients with GH. CONCLUSIONS: The biochemical hepatic iron index is a reliable method for establishing a diagnosis of homozygous GH. In contrast, the histological hepatic iron index as originally described is non-specific and does not reliably distinguish patients with GH from others with a raised hepatic iron index due to other causes. The specificity of this index can be improved by increasing the cut off level used, but the discrimination provided by the histological index is still inferior to that provided by the biochemical hepatic iron index.

Adult↗
PubMed1995

Characterization of lipoproteins containing a truncated form of apolipoprotein B, apolipoprotein B32.

We have characterized the lipoproteins isolated from the plasma of a human subject who was heterozygous for a mutation yielding a truncated apolipoprotein B (apo-B32). The apo-B32 lipoproteins were isolated from the plasma high density lipoprotein (HDL) fraction by heparin-Sepharose chromatography. Although the chemical composition of the apo-B32-containing lipoproteins was similar to that of normal HDL, the mean diameter of the apo-B32 lipoproteins was larger than typical apo-AI-containing HDL particles. On agarose gels, the apo-B32 lipoproteins had pre-beta mobility similar to that of normal very low density lipoproteins. Analysis of the purified apo-B32 lipoproteins by SDS-polyacrylamide gel electrophoresis revealed the presence of both apo-AI and apo-E. In order to further analyze the properties of apo-B32, we developed an apo-B32 expression vector and generated stable rat hepatoma cell lines expressing apo-B32. In these cell lines, the apo-B32 protein was secreted in a d > 1.21 g/ml lipoprotein. Oleic acid supplementation of the cell-culture media had no measurable affect on the density distribution of the apo-B32 lipoproteins that were secreted by the cells.

Animals↗
PubMed1995

Improved detection of Chlamydia trachomatis in endocervical samples by using a new polymerase chain reaction assay.

AIM: To compare the performance of a commercially developed polymerase chain reaction (PCR) assay, Amplicor Chlamydia trachomatis from Roche Molecular Systems, with that of a standard enzyme immunoassay (EIA) system, Chlamydiazyme from Abbott Laboratories, which is currently used throughout New Zealand. METHODS: Cervical swabs were collected from 819 female patients attending the family planning clinic in Christchurch. These swabs were then analysed using the Amplicor and Chlamydiazyme assays. RESULTS: The prevalence of chlamydia infection was 4.2% by the Chlamydiazyme EIA method and 5.3% with the Amplicor PCR assay. In 20 cases, where the results from the two assays were discordant, the conflict was 'resolved' by using a third assay which detects a separate region of the chlamydia genome. This gave an overall prevalence of 5.8% of confirmed infections in this group. The Amplicor PCR assay detected 29.4% more cases than the usual EIA method. CONCLUSIONS: This study demonstrates that Amplicor PCR assay allows improved identification of C trachomatis infections in a population with a relatively low prevalence of infection. The Amplicor PCR assay detects a significant number of additional infections and should be considered for routine use. As the PCR assay is more expensive a shift in the price/payment structure may be required before this assay comes into widespread use. However, the reduced morbidity resulting from the detection and treatment of otherwise unrecognised cases should also be considered in any cost benefit analysis.

Adult↗
PubMed1995

Endoproteolytic processing of recombinant proalbumin variants by the yeast Kex2 protease.

The yeast Kex2 protease is regarded as the prototype of the eukaryotic family of subtilisin-like serine proteases involved in processing after dibasic amino acid sequences. Here we investigate the specificity of Kex2 using recombinant human proalbumin variants. Proalbumins with the processing site sequences Arg-Arg and Lys-Arg were cleaved after the dibasic sequence at approximately the same rate by Kex2 in vitro, and yeast expressing either of these sequences secreted mature albumin into the culture medium. As expected, the Arg-Gly-Val-Phe-His-Arg-albumin (proalbumin Lille) was not a substrate for Kex2 and neither was the Arg-Gly-Arg-Phe-His-Arg-albumin. In contrast to the mammalian endoproteases furin and the hepatic proalbumin convertase, the Kex2 protease was adversely affected by a P4 arginine. There was an 85% decrease in the cleavage of Arg-Gly-Arg-Phe-Arg-Arg-albumin compared with normal; also chicken proalbumin with an Arg-Phe-Ala-Arg processing site sequence was not a substrate for Kex2. A P1' arginine had a marked negative effect on processing and N-terminal sequence analysis confirmed that cleavage was occurring at the P1-P1' bond. The sequence context surrounding the classical dibasic site is critical in determining susceptibility to cleavage by the Kex2 protease.

Animals↗
PubMed1995

Superoxide dismutase (glu100-->gly) in a family with inherited motor neuron disease: detection of mutant superoxide dismutase activity and the presence of heterodimers.

Superoxide dismutase glu100-->gly, a mutation known to be associated with familial motor neuron disease (familial amyotrophic lateral sclerosis) has been detected in one symptomatic and five of seven asymptomatic members of a family with a history of this disease. On average, the individuals with the mutation had 75% of normal red blood cell superoxide dismutase activity. Native polyacrylamide gels stained for superoxide dismutase activity showed two abnormal bands in the family members identified as carrying the mutation. This indicates that active mutant enzyme is present in red cells and forms stable homodimers and heterodimers with the normal chain. A silent mutation in exon 4, not associated with motor neuron disease, was also detected in one family member.

Amyotrophic Lateral Sclerosis↗
PubMed1995

Huntington's disease: diagnosis by amplification of the CAG repeat.

AIM: To develop and validate a test for the diagnosis of Huntington's disease by the direct detection, and sizing of, expanded CAG triplet repeats within the Huntington gene of affected individuals. METHODS: A polymerase chain reaction-based test which specifically amplifies the CAG repeat was developed using an ultra heat stable polymerase and [alpha 35S] delta ATP incorporation. Amplified alleles were separated on DNA sequencing gels and sized by comparison with a known sequence. RESULTS: Analysis of 10 affected individuals showed abnormal alleles with repeat numbers ranging from 40 to 61. In one case, that had been diagnostically uncertain because there was no family history of Huntington's disease, the demonstration of an expanded allele confirmed the diagnosis. Analysis of this patient's elderly and unaffected father indicated that he had an allele at the extreme end of the normal range. In a second case with atypical neurological features the diagnosis was also established by the demonstration of an expanded allele. CONCLUSIONS: This assay allows improved diagnosis of Huntington's disease including completely accurate presymptomatic and antenatal diagnosis. Easy access to this test has implications for clinical practice but acceptable guidelines for its use will need to be developed.

Adult↗
PubMed1995

Dermatologists and antibiotic prophylaxis: a survey.

BACKGROUND: Antibiotic prophylaxis is frequently used for the prevention of infection at a distant site such as the heart valve or prosthetic joint. However, there are no published data describing how dermatologists manage patients "at risk". OBJECTIVE: The purpose of this study is to document prophylactic antibiotic use by dermatologists. METHODS: A total of 211 randomly selected community dermatologists and 69 academic dermatologic surgeons were surveyed by questionnaire to determine whether they would provide antibiotic prophylaxis in 20 different clinical situations. RESULTS: This survey showed that under certain circumstances, almost all dermatologists provide antibiotic prophylaxis to prevent infection at a distant site. However, many dermatologists use antibiotics in settings with relatively little or no indication and confuse a prophylactic regimen with treatment of a superficial infection. CONCLUSION: This survey underscores the need for education and research into the prophylactic management of patients "at risk" who undergo dermatologic surgical procedures.

Academic Medical Centers↗
PubMed1995

A nicotinic acetylcholine receptor regulating cell adhesion and motility is expressed in human keratinocytes.

Acetylcholine is synthesized and released by human epidermal keratinocytes and modulates the adhesion and motility of these cells. To understand the molecular basis of the effects of acetylcholine on keratinocytes, we investigated the presence, pharmacology, structure, and function of nicotinic acetylcholine receptors in human epidermal keratinocytes. Patch-clamp studies indicated that keratinocytes express acetylcholine receptors with ion gating and pharmacologic properties similar to those observed so far only in neurons, and containing the alpha 3 subunit. Specific binding of the receptor-specific ligand 125I-kappa-bungarotoxin revealed approximately 5500 binding sites per cell on undifferentiated keratinocytes in cell cultures and approximately 35,400 binding sites per cell on mature keratinocytes freshly isolated from human neonatal foreskins. Antibody binding and polymerase chain reaction experiments demonstrated the presence of alpha 3, beta 2, and beta 4 nicotinic receptor subunits. Binding of subunit-specific antibodies indicated that nicotinic receptors were associated with the suprabasal keratinocytes in epidermis and localized to the cell membranes of differentiated keratinocytes in cell cultures. Acetylcholine and the nicotinic agonist nicotine increased cell-substrate and cell-cell adherence of cultured keratinocytes and stimulated their lateral migration. The specific antagonists kappa-bungarotoxin and mecamylamine caused cell detachment and abolished migration. Thus, a nicotinic receptor expressed in keratinocytes may mediate acetylcholine control of keratinocyte adhesion and motility.

Acetylcholine↗
PubMed1995

Aberrant hepatic processing causes removal of activation peptide and primary polymerisation site from fibrinogen Canterbury (A alpha 20 Val --> Asp).

A novel mechanism of molecular disease was uncovered in a patient with prolonged thrombin time and a mild bleeding tendency. DNA sequencing of the fibrinogen A alpha chain indicated heterozygosity for a mutation of 20 Val --> Asp. The molar ratio of fibrinopeptide A to B released by thrombin was substantially reduced at 0.64 suggesting either impaired cleavage or that the majority of the variant alpha chains lacked the A peptide. The latter novel proposal arises from the observation that the mutation changes the normal 16R G P R V20 sequence to R G P R D creating a potential furin cleavage site at Arg 19. Synthetic peptides incorporating both sequences were tested as substrates for both thrombin and furin. There was no substantial difference in the thrombin catalyzed cleavage. However, the variant peptide, but not the normal, was rapidly cleaved at Arg 19 by furin. Predictably intracellular cleavage of the Aalpha-chain at Arg 19 would remove fibrinopeptide A together with the G P R polymerisation site. This was confirmed by sequence analysis of fibrinogen Aalpha chains after isolation by SDS-PAGE. The expected normal sequence was detected together with a new sequence (D V E R H Q S A-) commencing at residue 20. Truncation was further verified by nonreducing SDS-PAGE of the NH2-terminal disulfide knot which indicated the presence of aberrant homo- and heterodimers.

Amino Acid Sequence↗
PubMed1994

Reference accuracy in the dermatologic literature.

BACKGROUND: The reference list is an important part of a scientific article. To be useful it must be accurate. OBJECTIVE: The purpose of this study was to evaluate the accuracy of references in the dermatologic literature. METHODS: We randomly selected 240 references (60 per journal) from the Archives of Dermatology, the British Journal of Dermatology, this Journal, and the Journal of Investigative Dermatology and checked them against the original articles. RESULTS: The overall rate of citation error (the information identifying the source) was 41%, and the quotation error (inconsistency between the statement referenced and the original source) was 35%. Only 36% of references were free of error. CONCLUSION: This study shows that the rate of citation and quotation errors is unacceptably high in the dermatologic literature, which significantly diminishes the value of the reference list.

Bibliometrics↗
PubMed1994

Thyroxine binding by human transthyretin variants: mutations at position 119, but not position 54, increase thyroxine binding affinity.

A mutation at codon 119 in the transthyretin (TTR) gene leads to a substitution of methionine for threonine at this position in the circulating protein. As the amino acid at position 119 is located in the T4 binding channel, mutations here may affect the binding of T4 by TTR. A previous study has shown an increase in the amount of hormone carried by the TTRMet119 variant. To determine whether this increase in binding was due to a change in affinity or capacity, TTR was partially purified from normal individuals and those with the TTRMet119 mutation. The isolation procedure was a rapid, single step passage through Blue Sepharose. With normal serum, the resulting protein bound T4 with a single site of intermediate affinity (Ka, 1.63 +/- 0.36 x 10(7) L/mol). No sites of higher or lower affinity were detected. Comparisons of binding capacity and immunoreactive TTR concentrations showed that the preparations bound T4 with a molar ratio between 1-2. With TTRMet119 serum, the T4 affinity was approximately doubled [Ka, 3.40 +/- 0.76 x 10(7) L/mol (+/- SD); P < 0.001] with no change in binding capacity. This doubling in affinity explains the observed T4 levels of about 120 nmol/L in individuals with this mutation. Binding of rT3 to TTRMet119 was increased approximately 5-fold over normal. Identical experiments with TTRGly54, in which glycine is substituted for glutamine, showed that the T4 affinity of this variant was unchanged from normal. These results suggest that the TTRMet119 mutation leads to secretion of a normal concentration of TTR that has a raised affinity for T4. Depending on their location, mutations in the TTR gene may lead to an increase or no change in T4 binding by the secreted protein.

Genetic Variation↗
PubMed1993

Lead exposure during recreational use of small bore rifle ranges.

AIMS: Following detection of symptomatic lead toxicity in two users of an indoor small bore rifle range, we studied users of several similar facilities to determine if significant recreational lead exposure occurred. METHOD: Red cell lead levels were measured at the end of a six month (winter) indoor shooting season and prior to commencement of shooting in the following year. Lead levels in air and dust sampled at one range were also measured. RESULTS: REd cell lead levels were elevated at the end of season (mean 2.64 mumol/L) and lower (mean 1.60 mumol/L) in the preseason samples. The average red cell lead level of the male shooters was 2.4 times normal and is comparable to the levels found in many occupationally exposed groups. Maximum air lead levels were 210 micrograms/m3, more than 2 times the Department of Labour OSH workplace exposure standard TWA of 100 micrograms/m3. Analysis of dust samples showed that dust at this range contained 24% to 36% lead. CONCLUSION: Although the mean time spent shooting was only 70 minutes per week the blood lead levels are similar to those previously reported for full time instructors at pistol ranges. This data confirms that lead exposure in recreational users of indoor small bore rifle ranges is a significant problem.

Adolescent↗