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Biomedical subjects

H R Matthews

Publications and source records attributed to H R Matthews.

At least 73 records · Page 4Linked to original sources
PubMed1992

Genistein inhibits protein histidine kinase.

Protein histidine kinase was prepared from whole cell extracts of the yeast, Saccharomyces cerevisiae. The enzyme was assayed using either histone H4 or a synthetic peptide corresponding to residues 70 to 102 of histone H4 as an in vitro substrate. With either substrate, both genistein and its solvent, dimethyl sulfoxide (Me2SO), inhibited protein histidine kinase. Me2SO alone gave a cooperative dose-response curve, with inhibition changing from almost zero below 10% Me2SO to 80% at 20% Me2SO with either substrate. Genistein gave a simple dose-response curve with 50% inhibition of protein histidine kinase at 110 microM genistein. In experiments with protein histidine kinase, genistein was a noncompetitive inhibitor with respect to ATP, histone H4 or the synthetic peptide, although, in the case of the synthetic peptide, the data were also consistent with competitive inhibition. These data gave Km values for both ATP and histone H4 of 15 microM, in satisfactory agreement with previously reported values (Huang, J., Wei, Y., Kim, Y., Osterberg, L., and Matthews, H. R. (1991) J. Biol. Chem. 266, 9023-9031). The Km for the synthetic peptide was 80 microM. The KI values were 270 or 310 microM measured with histone H4 or the synthetic peptide as substrate, respectively. While these KI values are relatively high, relative to published KI values for genistein inhibition of protein tyrosine kinases, many reported experiments use genistein at concentrations where inhibition of protein histidine kinase occurs. It is possible that some of the observed effects of genistein in vivo may be due to inhibition of protein histidine kinase.

Adenosine Triphosphate↗
PubMed1992

Voltage-dependent block by L-cis-diltiazem of the cyclic GMP-activated conductance of salamander rods.

Block by L-cis-diltiazem of the cyclic GMP-activated conductance was studied in excised inside-out patches from the salamander rod outer segment. When L-cis-diltiazem was applied from the cytoplasmic face of the patch, current suppression increased monotonically with membrane depolarization, the ratio of blocked to unblocked current varying e-fold in 50 mV. This suggests that L-cis-diltiazem interacts with a binding site located about half-way across the membrane field, and is unable to fully traverse the cyclic GMP-activated channel. The kinetics of block were accelerated by increasing L-cis-diltiazem concentration and by depolarization. These results can be fitted by a single barrier model in which the barrier peak is located about a third of the way across the membrane field from the cytoplasmic face. Application of L-cis-diltiazem from the extracellular face of the patch also resulted in an enhancement of block with membrane depolarization. Indirect evidence supports the notion that this block resulted from partition of the unchanged form of the blocker across the membrane, and its subsequent interaction with the cytoplasmic face of the conductance.

Ambystoma↗
PubMed1992

The ultrastructure of oesophageal carcinomas: multidirectional differentiation. A transmission electron microscopic study of 43 cases.

Forty-three oesophageal carcinomas, comprising 15 squamous cell carcinomas, 22 adenocarcinomas, 5 small cell carcinomas, and 1 adenosquamous carcinoma, were examined by transmission electron microscopy. The ultrastructural features of each tumour type are detailed. Multi-directional differentiation (heterogeneity) was observed in 11 cases: 5 squamous cell carcinomas with focal glandular features; 4 adenocarcinomas with focal squamous features; and 2 small cell carcinomas, one with glandular and the other with squamous features. Abnormal distributions of desmosomes in squamous cell carcinomas and of polarity of tumour cells in adenocarcinomas are described.

Adenocarcinoma↗
PubMed1992

The role of cytoplasmic calcium in photoreceptor light adaptation.

The process of light adaptation in vertebrate rod and cone photoreceptors is believed to involve a diffusible cytoplasmic messenger. Two lines of evidence indicate that photoreceptor light adaptation is mediated by a light-induced fall in cytoplasmic calcium concentration (Ca2+i). First, if changes in calcium concentration are slowed by the incorporation of calcium chelators into the photoreceptor cytoplasm then light adaptation is slowed also. Second, if the normal control of Ca2+i is prevented by simultaneously minimising calcium influx and efflux across the outer segment membrane by means of external solution changes, then all of the manifestations of light adaptation are abolished. Furthermore, recent results show that changes in Ca2+i imposed in the absence of light are sufficient to cause at least some of the manifestations of light adaptation. Together these results indicate that calcium acts as the messenger of light adaptation in the photoreceptors of both lower and higher vertebrates.

Adaptation, Physiological↗
PubMed1992

Effects of chemotherapy on ultrastructure of oesophageal adenocarcinoma.

AIMS: To compare and contrast the ultrastructural appearance of resected oesophageal adenocarcinomas treated with preoperative chemotherapy with that of non-treated resected controls; and to determine the usefulness of this method in the assessment of the effectiveness of the chemotherapeutic regimen. METHODS: Ten resected oesophageal adenocarcinomas treated with preoperative chemotherapy--mitomycin-C, ifosfamide, and cisplatin (MIC)--were examined by transmission electron microscopy and their appearance compared with that of 13 concurrent untreated resected oesophageal adenocarcinomas. RESULTS: The treated adenocarcinomas showed cytotoxic damage although complete tumour eradication was not achieved. In all 10 treated cases a variable proportion of the neoplastic cells showed unusual degenerative and necrotic changes not seen in untreated cases. In the most affected carcinomas the stroma contained increased numbers of inflammatory cells. CONCLUSIONS: This ultrastructural method is useful for the assessment of the in vivo effect of MIC.

Adenocarcinoma↗
PubMed1991

Photoaffinity polyamines: sequence-specific interactions with DNA.

ANB-spermine is a photoaffinity analog of the naturally-occurring polyamine, acetylspermine. ANB-spermine was used to determine its binding sites on naked double stranded DNA, at the nucleotide level, using a modification of the primer extension technique. A total of 1,275 nucleotides was examined in 5 sequences of DNA from Saccharomyces cerevisiae. Binding sites were non-random. The primary determinant of binding was the presence of a thymidine residue. Secondary determinants appeared to depend on the secondary structure of the DNA, with runs of thymidines providing unusually poor binding sites while TA and, especially, TATA providing the strongest binding sites. The 'TATA element' upstream of the URA3 gene from S. cerevisiae was the strongest binding site. The data indicate that ANB-spermine binding to DNA is a probe for DNA secondary structure and suggest a role for polyamines in regulating the structure of chromatin in vivo.

Azides↗
PubMed1991

Purification of a protein histidine kinase from the yeast Saccharomyces cerevisiae. The first member of this class of protein kinases.

An enzyme of molecular weight 32,000 comprising a single subunit has been isolated from whole cell extracts of the yeast Saccharomyces cerevisiae. In vitro, the enzyme transfers the gamma phosphate of ATP to a protein substrate, histone H4, to produce an alkali-stable phosphorylation. Modification of the substrate histidine with diethylpyrocarbonate prevented phosphorylation. Phosphoamino acid analysis of the phosphorylated substrate showed the presence of 1-phosphohistidine. Hence, the isolated enzyme is a protein histidine kinase. A novel assay for acid-labile alkali-stable protein phosphorylation was used in the purification of the kinase activity to a final specific activity of 2,700 nmol/15 min/mg. The purified enzyme phosphorylates specifically histidine 75 in histone H4 and does not phosphorylate histidine 18 nor histidine residues in any other core histone. Steady state kinetic data are consistent with an ordered sequential reaction with Km values for Mg-ATP and histone H4 of 60 and 17 microM, respectively. The protein histidine kinase requires a divalent cation such as Mg2+, Co2+, or Mn2+ but will not use Ca2+, Zn2+, Cu2+, Fe2+, spermine, or spermidine. This is the first purification of an enzyme that catalyzes N-linked phosphorylation in proteins.

Adenosine Triphosphate↗
PubMed1991

Two new photoaffinity polyamines appear to alter the helical twist of DNA in nucleosome core particles.

Two new photoaffinity derivatives of polyamines have been synthesized by the reaction of spermine or spermidine with methyl 4-azidobenzimidate. The new compounds were purified chromatographically and characterized by several methods including proton magnetic resonance spectroscopy. The spermine derivative is N1-ABA-spermine [(azidobenzamidino)spermine], and the spermidine derivative is a mixture of N1- and N8-ABA-spermidine. ABA-spermine stabilizes nucleosome core particles in thermal denaturation experiments, with similar but not identical effects when compared with the parent polyamine, spermine. In circular dichroism experiments, ABA-spermine was capable of producing a B----Z transition in poly(dG-m5dC) at a concentration of 30 microM, compared with 5 microM required to produce the same effect with spermine. On the other hand, ANB-spermine [(azidonitrobenzoyl)spermine; Morgan, J. E., Calkins, C. C., & Matthews, H. R. (1989) Biochemistry 28, 5095-5106] stabilized the B form of poly(dG-br5dC). ABA-spermine is a potent inhibitor of ornithine decarboxylase from Escherichia coli, giving 50% inhibition at 0.12 mM, while ANB-spermine is a modest inhibitor, comparable to spermine or spermidine. Under conditions of nitrogen-limited growth, yeast take up ABA-spermine and ABA-spermidine at approximately one-third to half the rate of spermidine or spermine. In contrast, ANB-spermine was not significantly taken up. The photoaffinity polyamines were used to photoaffinity label the DNA in nucleosome core particles, and the sites of labeling were determined by exonuclease protection. All photoaffinity reagents showed both nonspecific labeling and specific sites of higher occupancy. However, the positions of the sites varied: the ANB-spermine sites confirmed those previously reported (Morgan et al., 1989); the ABA-spermine and ABA-spermidine sites were spaced at 9.8 bp intervals from the 3' end of each DNA strand. This observation, together with the effect of spermine on the circular dichroism of DNA in nucleosome core particles, implies that polyamines alter the helical twist of DNA in nucleosome core particles. The ABA-polyamines are offered as general-purpose photoaffinity polyamine reagents.

Affinity Labels↗
PubMed1991

Assessment of the response to chemotherapy in oesophageal cancer.

Thirty-eight patients with localised oesophageal carcinoma have been studied by computed tomography (CT) and barium swallow before and after preoperative chemotherapy and the results correlated with the pathological findings in the resected specimen. Overall 48% of patients showed a complete or partial response to chemotherapy on CT, compared with 50% on barium and 94% on pathological examination. This study highlights deficiencies in CT scanning and barium swallow as methods of assessing the regression of tumor bulk following chemotherapy for oesophageal carcinoma. We suggest that strict and specific criteria will have to be laid down before the results of chemotherapy in this disease can be reliably and accurately evaluated.

Aged↗
PubMed1991

A phase II study of 5-fluorouracil, adriamycin and mitomycin-C in adenocarcinoma of the oesophagus.

We have evaluated the effect of 5-fluorouracil 600 mg/m2, doxorubicin ('Adriamycin') 40 mg/m2, and Mitomycin-C 4 mg/m2 (FAM) in two groups of patients with adenocarcinoma of the oesophagus, as either a preoperative or primary treatment. Response was assessed by barium swallow, CT scan, and measurement of metastases where present. Toxicity was as reported for FAM in gastric cancer. In the operated group 8 of 22 patients (36%) showed a partial response following two courses of FAM. Resection was completed in 20 patients, with six hospital deaths (30%). Of the 14 patients who were discharged from hospital, 8 have died (median 8 months) and 6 are alive at 12 to 27 months, with known recurrence in 1. In the non-operated group 6 of 17 patients (35%) showed a response, one complete, following one to six (mean 4.2) courses of FAM. Fifteen patients have died (median 5 months), and 2 are alive and free from disease at 12 and 17 months. Neoadjuvant therapy with FAM in adenocarcinoma of the oesophagus offers no advantage over surgery alone, although with inoperable disease FAM may be of use in palliation.

Adenocarcinoma↗
PubMed1991

Minitracheotomy Seldinger--assessment of a new technique.

A multicentre, prospective study of 26 patients was undertaken for the assessment of insertion of minitracheotomy tubes by the Seldinger technique. The technique of insertion is described. There were two misplacements, three blockages of the inserting Tuohy needle with fat, and six cases of difficulty in passing the minitracheotomy tube.

Anesthesia, Local↗
PubMed1991

Incorporation of chelator into guinea-pig rods shows that calcium mediates mammalian photoreceptor light adaptation.

1. The effects of steady light on the sensitivity and kinetics of the photocurrent response were studied in the rod photoreceptors of the guinea-pig, using suction pipette recordings of circulating current. 2. The sensitivity of the flash response decreased with increasing background intensity according to Weber's law. Ultimately for the brightest backgrounds saturation ensued. The recovery phase of the flash response was accelerated by steady light, while the early rising phase was little affected. 3. These results indicate that guinea-pig rods adapt to light in much the same way as do the rods and cones of lower vertebrates. 4. The role of cytoplasmic calcium concentration in this adaptation was studied by incorporation of the calcium chelator bis(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid (BAPTA) into the rod cytoplasm. Superfusion with a solution containing the membrane-permeant acetoxymethyl ester resulted in progressive changes in the response to light. 5. BAPTA incorporation retarded the falling phase of the flash response, thereby increasing receptor sensitivity, but did not affect the early rising phase of the response. BAPTA also slowed the adaptation of the response to steady illumination. 6. These results indicate that cytoplasmic calcium concentration plays a similar role in the light adaptation of guinea-pig rods to that in the adaptation of the rods and cones of lower vertebrates. Calcium therefore appears to act as the messenger of light adaptation in mammalian rods.

Action Potentials↗
PubMed1991

Results of thoracotomy in osteogenic sarcoma with pulmonary metastases.

BACKGROUND Resection of pulmonary metastases may be followed by long term survival and now that it is an accepted method of treatment for patients with osteogenic sarcoma indicators of favourable prognosis are needed to aid the assessment of suitability for resection. This study compares the survival rates of patients who did and did not undergo resection of their pulmonary metastases and relates them to prognostic indicators. METHODS The study population was the 43 patients with osteosarcoma who developed pulmonary metastases out of the 111 patients with osteosarcoma treated by the Birmingham bone tumour treatment service during 1977-83. All patients who developed metastases confined to the lungs were considered for resection, thoracotomy being advised for all patients (provided that they were fit enough) who had metastases thought to be resectable even if they were multiple. RESULTS Of the 18 patients who did not have a thoracotomy, 15 died of disseminated disease after a mean interval of eight months; one patient died of cardiomyopathy and two are alive after 26 and eight months. Of the 25 patients who underwent thoracotomy in an attempt to resect metastases, three were found to have inoperable disease and died after a mean interval of 5.4 months from thoracotomy. Overall, after thoracotomy (repeated if necessary) there was a 20% survival at five years from the first thoracotomy. When survival was assessed with respect to the disease free interval and the number and bilaterality of the metastases no significant relationships were found. There was, however, a significant relation between survival and the position of metastases, patients with metastases confined to one lobe of the lung having a mean survival of 29.5 months, compared with 13.7 months in patients with disease in more than one lobe. CONCLUSION Thus patients who had a thoracotomy survived longer from the time of diagnosis of pulmonary metastasis than those not undergoing thoracotomy; metastases confined to one lobe predicted a better prognosis.

Adolescent↗
PubMed1991

Surgical treatment of massive hydrothorax complicating continuous ambulatory peritoneal dialysis.

Acute hydrothorax is a well-recognized complication of continuous ambulatory peritoneal dialysis and is often regarded as a contraindication to its use. We report three cases treated by surgical closure of a communication between the peritoneal and pleural cavities enabling CAPD to continue successfully. This is a simple, safe and effective procedure which merits wider use as an alternative to transferring the patient to permanent hemodialysis.

Aged↗
PubMed1990

A filter-based protein kinase assay selective for alkali-stable protein phosphorylation and suitable for acid-labile protein phosphorylation.

Alkali-stable phosphorylation of proteins, particularly phosphotyrosine and phosphohistidine, is an important phenomenon in cells. In the case of phosphohistidine and some other phosphoamino acids, the phosphorylation is acid-labile and in these cases studies have been severely limited by the absence of a rapid assay suitable for acid-labile phosphorylation. The assay presented here involves a conventional kinase assay reaction followed by mild alkaline hydrolysis and adsorption of the product to washed Nytran paper at high pH. After further washing, at pH 9, the radioactivity on the papers is determined by liquid scintillation counting. Hence, acid-labile phosphorylation is preserved. The assay is selective for alkali-stable phosphorylation but not fully specific, mainly due to the need to balance the severity of the partial alkaline hydrolysis with the stability of the protein-peptide bonds. The assay has been used for the purification and characterization of a protein histidine kinase from Saccharomyces cerevisiae.

Histidine↗
PubMed1990

Application of sodium dodecyl sulfate-gel electrophoresis to low molecular weight polypeptides.

Experiments with nine polypeptides with molecular weights between 2000 and 10,760 confirm the value of sodium dodecy sulfate (SDS)-gel electrophoresis for separating polypeptides in this molecular weight range. In one case, electrophoretic blotting and microsequencing were successfully carried out. However, molecular weight determination in the low molecular weight range (less than 10,000) is much less reliable than that in the conventional molecular weight range (greater than 10,000) for SDS gels. Information provided by suppliers of horse heart myoglobin fragment kits is potentially misleading.

Animals↗
PubMed1990

Calcium and the mechanism of light adaptation in vertebrate photoreceptors.

Vertebrate photoreceptors transduce the absorption of light into a hyperpolarizing change in membrane potential. The mechanism of transduction is becoming fairly well understood and has been shown to occur via a G protein-coupled decrease in cyclic GMP. Attention is now turning to the way the enzymatic machinery in the outer segment of the photoreceptor cell is modulated during light adaptation. Recent studies show that light adaptation cannot occur if changes in the concentration of cytoplasmic free calcium in the outer segment are prevented, suggesting that calcium functions as a second messenger in sensitivity regulation.

Adaptation, Physiological↗