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Biomedical subjects

M A Harrison

Publications and source records attributed to M A Harrison.

68 records · Page 4Linked to original sources
PubMed1975

Abscisic Acid Metabolism in Water-stressed Bean Leaves.

Phaseic acid (PA) and dihydrophaseic acid (DPA) are the major metabolites observed when (S)-2-(14)C-abscisic acid (ABA) is fed to 14-day excised primary bean leaves (Phaseolus vulgaris L. cv. Red Kidney). The distribution of (14)C in leaves which were wilted after feeding ABA appears to be the same as that observed in unwilted leaves. A reduction in the relative specific radioactivities of the two metabolites after wilting, compared with the specific radioactivities measured in unwilted plants, indicated that these metabolites continue to be formed endogenously after wilting. Estimates of the endogenous ABA levels showed that they rose from 0.04 mug to approximately 0.5 mug/g fresh weight within 4 hours after the beginning of a 10% wilt and remained at that level during a subsequent 20 hours of wilt. In unwilted leaves, the levels of PA and DPA were 5 times and 20 times higher than that of ABA, respectively. Both PA and DPA levels rose throughout the wilt period. PA rose from 0.20 mug to 1.0 mug and DPA from 0.8 mug to over 3 mug/g fresh weight. From these data, we calculated the rate of ABA synthesis to be at least 0.15 mug/hr.g fresh weight during this period. We have interpreted these results to mean that in wilted leaves an elevated level of ABA is maintained because the rate of synthesis and metabolism are both elevated and approximately equal.

Journal Article↗
PubMed1975

Fibroxanthosarcoma of bone.

A tumour arising from the body of the eighth thoracic vertebra is believed to be the first recordedexample of a primary fibroxanthosarcoma of bone. Apart from the absence of a demonstrable storiform pattern, the histology conformed to that of fibroxanthosarcoma of the soft tissues. Ultrastructural studies showed that asteroid-like bodies seen in the cytoplasm of some tumour cells consisted of aggregated centrioles surrounded by cytoplasmic vacuoles. The finding of Langerhans cell granules in some tumour cells supported their identification as histiocytes. These granules have not previously been recorded in the fibrous histiocytoma group of tumours.

Aged↗
PubMedDate not supplied

Protein phosphorylation and control of excitation energy transfer in photosynthetic purple bacteria and cyanobacteria.

The function of phosphorylation of light-harvesting polypeptides is well characterised in chloroplasts of green plants, but the prokaryotic cyanobacteria and purple photosynthetic bacteria have quite different light-harvesting polypeptides whose structure and function cannot be controlled in precisely the same way. Nevertheless, cyanobacteria show light-dependent phosphorylation of membrane polypeptides associated with photosystem II and with the light-harvesting phycobilisome, and purple bacteria show light-dependent phosphorylation of low molecular-weight chromatophore membrane polypeptides. In both cases membrane protein phosphorylation is associated with functional changes observed by chlorophyll fluorescence spectroscopy or chlorophyll fluorescence induction kinetics. Here we report on our recent protein sequence and other data concerning the identities of these phosphoproteins. We also discuss the significance of these findings for regulation by protein phosphorylation of photosynthesis in prokaryotes.

Cyanobacteria↗
PubMedDate not supplied

Spectrum of osteoblastic differentiation in new cell lines derived from spontaneous murine osteosarcomas.

Cell lines were established from three spontaneous osteosarcoma and one fibrosarcoma of aging mice. They were studied for tumorigenicity, osteoblastic features, and other in vitro cellular characteristics, by a combination of histological, morphological, biochemical, and molecular approaches. It was found that all cell lines formed tumors in vivo, whereas in vitro, only the fibrosarcoma-derived cell line grew efficiently in soft agar. Three out of the four cell lines produced mouse endogenous retroviruses, but none were classical sarcoma viruses. Type I collagen was expressed by all the cell lines, as was another extracellular matrix protein, osteonectin. The osteosarcoma-derived cell lines, however, exhibited different degrees of osteogenic differentiation. Only one line (OSA), and its clonal subline (1G11), consistently gave rise to mineralized tumors after transplantation into syngeneic mice, and these cells expressed high levels of alkaline phosphatase and bone-specific osteocalcin mRNA in vitro. Expression of these biochemical markers of osteoblasts occurred to a lesser extent in a second line (OSC) and was undetectable in the third line (OSB). The clonal 1G11 cell line exhibits the phenotype of a fully mature osteoblast and thus may serve as a particularly useful model for studies of bone cell function and regulation. Studies of cells which display a wide spectrum of osteogenic potential may further our understanding of the mechanisms involved in bone cell differentiation and tumorigenicity.

Alkaline Phosphatase↗
PubMedDate not supplied

Expression, purification and secondary structure analysis of Saccharomyces cerevisiae vacuolar membrane H+-ATPase subunit F (Vma7p).

The vacuolar H+-ATPase is an acid pump found in virtually all eukaryotic cells. It shares a common macromolecular organization with the F1F0-ATPase, and some V-ATPase subunits are structural and functional homologues of F-ATPase components. However, the vacuolar complex contains several subunits which do not resemble F-ATPase subunits at the sequence level, and which currently have no specific function assigned. One example is subunit F, the Vma7p polypeptide of Saccharomyces cerevisiae. A recombinant form of Vma7p was expressed in Escherichia coli and purified to homogeneity. Mass spectroscopy confirmed a mass of 13460 Da for Vma7p, and dynamic light scattering showed that the polypeptide was globular and monodisperse even at high concentrations. Analysis of secondary structure by circular dichroism and FTIR showed that Vma7p comprises 30% alpha-helix and 32-42% beta-sheet. The protein fold recognition programme 'Threader 2' produced highly significant matches between Vma7p and five alpha-beta sandwich folds. Relative proportions of secondary structure elements within these folds were broadly consistent with the spectroscopic data. Although Vma7p does not share sequence similarity with the F-ATPase epsilon subunit, the analysis suggests that the polypeptides not only have similar masses and assemble into homologous core complexes, but also share similar secondary structures. It is possible that the two polypeptides are homologous and perform similar functions within their respective ATPases. The production of high yields of homogeneous, folded, monodisperse protein will facilitate high resolution crystallography and NMR spectroscopy studies.

Circular Dichroism↗
PubMedDate not supplied

Detection of preformed type A botulinal toxin in hash brown potatoes by using the mouse bioasssay and a modified ELISA test.

A foodborne illness caused by type A toxin-producing Clostridium botulinum was investigated by using the standard mouse bioassay and a rapid invitro test for toxin detection. The patient, who consumed improperly stored hash brown potatoes that contained the preformed toxin, was diagnosed with type A botulism. C. botulinum type A toxin was detected in the hash brown potatoes as well as in the tryptone-peptone-glucose-yeast extract (TPGY) medium subcultures of this food using the mouse bioassay and an amplified ELISA technique. The mouse bioassay revealed preformed toxin at 10,000 minimum lethal dose (MLD)/g uncooked product and the amplified ELISA an equivalent 50,000 MLD/g. The cultural toxin from the uncooked product killed mice at the 10(6) dilution and a modification of the ELISA procedure was positive at the 10(3) dilution. Cooked food obtained from the consumer's waste can contained 100 MLD/g and the ELISA was also positive at the same dilution of the product. The culture of the cooked product obtained from the waste can was lethal for mice at the 10(7) dilution and positive using the modified ELISA at the 10(4) dilution. The unmodified amplified ELISA method indicated a toxin level of approximately 1 ng/mL (equivalent to 5 x 10(5) MLD/mL) in diluted culture fluid from the uncooked food and the culture of cooked food obtained from the waste can. The hash brown potatoes were negative for types B, E, and F preformed and cultural botulinal toxins using both assays.

Animals↗