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Biomedical subjects

J C Gray

Publications and source records attributed to J C Gray.

At least 109 records · Page 6Linked to original sources
PubMed1985

The wheat chloroplast gene for CF(0) subunit I of ATP synthase contains a large intron.

The gene for CF(0) subunit I of ATP synthase has been located in wheat chloroplast DNA, between the genes for CF(0) subunit III and alpha subunit of CF(1). Nucleotide sequencing and analysis of RNA-DNA hybrids indicated that the gene is interrupted by an 823-bp intron which has boundaries similar to those previously described for the introns in protein-coding chloroplast genes of Euglena gracilis. The deduced amino acid sequence of CF(0) subunit I indicates a polypeptide of 183 amino acid residues. However, N-terminal amino acid sequencing of the mature spinach CF(0) subunit I suggests that the protein is synthesised with a N-terminal extension of 17 amino acid residues and is processed to give a protein of mol. wt. 19 001 of 166 amino acids residues. The mature CF(0) subunit I shows similarities in primary and predicted secondary structure to F(0) subunit b of Escherichia coli ATP synthase. A major transcript of 3.3 kb containing sequences from the genes for CF(0) subunit III, subunit I and CF(1) subunit alpha has been observed by RNA-DNA hybridisation.

Journal Article↗
PubMed1985

Binding of pea cytochrome f to the inner membrane of Escherichia coli requires the bacterial secA gene product.

Various sequences from the 5' end of the pea chloroplast gene for cytochrome f have been fused in the correct reading frame with lacZ, and the cellular location of the hybrid polypeptides in Escherichia coli has been examined. Hybrid polypeptides containing N-terminal parts of cytochrome f are located in the cytoplasmic membrane of E. coli. Membrane localization is most efficient when the intact signal sequence of cytochrome f is present at the N-terminal end of the fusion proteins. Fusion within the signal sequence, so that the processing site is absent, reduces the efficiency of membrane binding. Membrane insertion of fusion proteins containing signal sequences is prevented in a temperature-sensitive secA strain at the nonpermissive temperature and the hybrid proteins accumulate in the cytoplasm. This indicates that specific recognition of the chloroplast signal sequence occurs in the bacterial secretory pathway.

Bacterial Proteins↗
PubMed1984

Synthesis of wheat leaf nitrite reductase de novo following induction with nitrate and light.

Nitrite reductase has been purified almost 3000-fold, in 35% yield, to a specific activity of 77 units (mg protein)-1 from wheat leaves using a multi-step procedure with affinity chromatography on ferredoxin-Sepharose as the final step. The purified enzyme, although not homogeneous, exhibited absorption maxima at 278, 390, 568 and 687 nm. Minor contaminants were removed by gel filtration in the presence of sodium dodecyl sulphate to yield a single polypeptide of Mr 60 500 as judged by polyacrylamide gel electrophoresis. Antibodies raised against this polypeptide were shown to cross-react with native nitrite reductase and were used to study the synthesis of nitrite reductase in vivo and in vitro. The increase in nitrite reductase activity following exposure of dark-grown plants to nitrate and light was shown by immunodecoration of Western blots to be due to synthesis de novo. Poly(A)-rich RNA isolated from plants actively synthesising nitrite reductase was shown to direct the synthesis in a rabbit reticulocyte lysate of a polypeptide of Mr 64000 which was immunoprecipitated by antibodies to nitrite reductase.

Cell-Free System↗
PubMed1984

Synthesis of components of the cytochrome b-f complex by isolated pea chloroplasts.

Three components of the cytochrome b-f complex, cytochrome f, cytochrome b-563 and a 15.2-kDa polypeptide, were labelled with radioactive amino acids in isolated pea chloroplasts incubated in the light with added Mg-ATP. The assembly of cytochrome b-563 (19.5 kDa) into the cytochrome complex required the presence of added Mg-ATP whereas cytochrome f (37.3 kDa) and the 15.2-kDa polypeptide were assembled in its absence. Incorporation of [35S]methionine into the polypeptide chain of cytochrome b-563 and the 15.2-kDa component was confirmed by peptide mapping of the products of partial digestion with papain.

Adenosine Triphosphate↗
PubMed1984

Structure and topology of cytochrome f in pea chloroplast membranes.

A transmembrane arrangement of cytochrome f in chloroplast thylakoid membranes, with the N-terminal heme-containing region in the intrathylakoid space and a 15 amino acid C-terminal sequence in the stroma, is suggested by the amino acid sequence deduced from the nucleotide sequence of the pea chloroplast gene. This topology has been confirmed by partial proteolysis of the polypeptide in intact and disrupted thylakoid membranes and in inside-out and right-side-out vesicles of chloroplast membranes.

Amino Acid Sequence↗
PubMed1983

Isolation and characterization of a cytochrome b-f complex from pea chloroplasts.

A cytochrome b-f complex has been extracted from pea chloroplast membranes with octyl glucoside and cholate and has been purified by ammonium sulphate fractionation and polyacrylamide gel electrophoresis in the presence of Triton X-100 and sodium deoxycholate. The complex contains cytochromes f and b-563 in a ratio of 1:2, but shows very low levels of the Rieske iron sulphur centre and plastoquinol-plastocyanin oxidoreductase activity. The complex consists of four polypeptides of molecular weights 37300, 34000, 19500 and 15200. The complex is dissociated by electrophoresis in the presence of 2M urea to give pure preparations of cytochrome f and cytochrome b-563, which on sodium dodecylsulphate-polyacrylamide gel electrophoresis give single bands of apparent molecular weights 37300 and 19500 respectively.

Chloroplasts↗
PubMed1982

Location and nucleotide sequence of the gene for the proton-translocating subunit of wheat chloroplast ATP synthase.

The proton-translocating subunit of wheat chloroplast ATP synthase is encoded by a chloroplast gene that has been accurately mapped and whose nucleotide sequence has been determined. The predicted sequence of 81 amino acids has been confirmed in part by determination of the sequence of the first 40 amino acids from the NH(2) terminus of the protein, and it shows 100% homology with the known amino acid sequence of the spinach protein but no more than 35% homology with the amino acid sequences of bacterial and mitochondrial proteins. The gene shows no deviation from the "universal" genetic code and is not split. A potential ribosome binding site is located 12 nucleotides upstream from the initiation codon, but sequences homologous to prokaryotic promotors and transcription terminators are not apparent.

Journal Article↗
PubMed1982

Donor cells' contribution to osteogenesis in experimental cancellous bone grafts.

Osteogenesis in subcutaneous, cancellous bone isografts in the rat was assessed at 16 days from the uptake of 85Sr. by comparing the uptake in grafts devoid of one or more cellular components, the contribution of each to osteogenesis was estimated. The per cent contribution of each of the osteogenetic elements was: endosteal lining cells together with marrow stroma, 60%; periosteal cells, 30%; free, hemopoietic marrow cells and osteocytes, no significant contribution. These findings are compared with those previously reported for cortical bone isografts and it appears that the rate of osteogenesis is 2.2 times higher in cancellous grafts than in cortical grafts of the same weight, but only 1.7 times higher when grafts of the same volume are compared. Osteogenetic and hemopoietic activities associated with marrow appear to arise from different groups of cells. It is shown how, with iliac bone marrow, these two groups of cells may be separated physically, the hemopoietic cells being removed by means of a jet of saline, and the osteogenetic cells by subsequent enzyme treatment plus a second jet of saline. The osteogenetic and hemopoietic elements were difficult to separate from bone marrow within the femoral diaphysis.

Animals↗
PubMed1981

Osteogenesis in bone grafts after short-term storage and topical antibiotic treatment. An experimental study in rats.

It has been shown in experimental animals that the living cells in a bone autograft can make an important contribution to osteogenesis. However, some common clinical techniques, such as the topical use of antibiotic powders on grafts or on the graft bed, are likely to damage or kill the cells. In this experimental study in rats, bone isografts dusted with chloramphenicol or methicillin powder or with Polybactrin spray before subcutaneous implantation produced little or no new bone over a period of two weeks whereas untreated, control grafts showed abundant osteogenesis, as did grafts pretreated with solutions of antibiotics. The effect of short-term storage of the grafts for 3 to 24 hours in air, saline or culture medium before implantation was also examined. Grafts stored in culture medium generally did as well as, or better than, fresh control grafts whereas immersion in saline inhibited osteogenesis. The importance of these results for clinical bone grafting is discussed.

Animals↗
PubMed1980

The effects of thermal environment on heat balance and insensible water loss in low-birth-weight infants.

To define the neutral environmental temperature and assess the effects of deviation from that temperature on insensible water loss and heat balance, 12 premature infants were studied in a conventional incubator at four different predetermined ambient temperatures. Our method combines insensible water loss measured by a continuous read-out electronic scale with heat production as determined by open circuit measurement of oxygen consumption. An increase of 1 to 2 degrees C, to an ambient temperature above or near the top of the neutral zone, produced a significant rise in insensible water loss, from 1.90 +/- 0.76 to 3.08 +/- 1.19 ml/kg/hour (mean +/- SD), a corresponding rise in evaporative heat loss, and a fall in nonevaporative heat loss. A decrease of 1 to 2 degrees C, to a slightly subneutral ambient temperature, resulted in an increase in oxygen consumption from 5.82 +/- 0.92 to 7.45 +/- 1.50 ml/kg/minute, and an increase in total heat loss, but no change in insensible water loss and evaporative heat loss. The increased total heat loss was judged to be due entirely to a greater nonevaporative heat loss, both by convection and by radiation. The data confirm that ambient temperature is an important determinant of the magnitude and the partition of heat loss in low-birth-weight infants.

Body Temperature Regulation↗
PubMed1980

Maternal inheritance of cytochrome f in interspecific Nicotiana hybrids.

Cytochrome f has been purified to homogeneity, as judged by polyacrylamide gel electrophoresis, from the leaves of Nicotiana tabacum, Nicotiana glutinosa and their reciprocal hybrids. The cytochrome was extracted from chloroplast membranes by sonication in 2% Triton X-100 and 4M urea and was subsequently purified by acetone precipitation and chromatography on Ultrogel AcA 22 in the presence of cholate and on Sephadex G-200 in the presence of sodium dodecylsulphate. The purified cytochrome had a molecular weight of 32,700 determined by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. A difference in the primary structure of cytochrome f from N. tabacum and N. glutinosa was detected by ion-exchange chromatography of the products of trypsin hydrolysis. Cytochrome f from N. tabacum contained an additional peptide not present in the cytochrome fom N. glutinosa. This additional peptide was present in the cytochrome from N. tabacum female x N. glutinosa male, but not in the cytochrome from N. glutinosa female x N. tabacum male, indicating a maternal mode of inheritance of the primary structure of cytochrome f. This suggests an extranuclear, probably chloroplast, location for the genetic information for cytochrome f.

Amino Acids↗
PubMed1979

Early osteogenesis in compact bone isografts: a quantitative study of contributions of the different graft cells.

Isografts of cortical bone were tranplanted subcutaneously in the rat and the rate of osteogenesis 12 to 14 days later was assessed by measurement of 85Sr uptake and by histology. Some grafts were implanted complete whereas others had had one or more of their cellular components (viz. periosteum, endosteum, osteocytes, marrow) removed by mechanical or enzymatic pretreatment. From an analysis of the differences in osteogenesis between grafts devoid of different combinations of cellular components, the contribution of each component to osteogenesis was determined. The results indicate that the endosteal lining cells and marrow stroma together produce more than half of the new bone, the periosteal cells contribute about 30%, the osteocytes possibly make a small (10%) contribution, and the free, hemopoietic cells of the marrow make no significant contribution. Evidence about the relative contributions to osteogenesis of graft and host cells is reviewed and the possible osteogenetic role of bone marrow is discussed.

Animals↗