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K S Booth

Publications and source records attributed to K S Booth.

10 recordsLinked to original sources
PubMed1996

Cryopreservation of an attenuated vaccine strain of the protozoan parasite Toxoplasma gondii.

Toxoplasma gondii is a protozoan parasite that infects birds and mammals, including humans. T. gondii T-263 is an attenuated mutant strain that is being developed as a live vaccine to protect cats from shedding oocysts. A cryopreservation procedure for T. gondii T-263 bradyzoites has been developed to meet the requirement for product stability. A Me2SO-based procedure for the cryopreservation of tachyzoites was used as a basis for process optimization. A modified cell culture plaque assay was used to determine the effects of selected cryobiological parameters on bradyzoite viability. The major parameters evaluated were: (i) cooling rates; (ii) intermediate plunge temperature; and (iii) thawing and dilution rates and temperatures. The optimized cryopreservation protocol comprised incubation in 12.5% Me2SO and 4% BSA for 30 min at room temperature, cooling at 1 degree C min-1 to -40 degrees C, followed by direct transfer into liquid nitrogen. Rapid thawing (approximately 120 degrees C min-1) followed by slow dilution of cryoprotectant over 15 min resulted in the highest survival. The optimized procedure increased survival 10,000-fold over that obtained using an established tachyzoite protocol. This procedure is to be adapted for the large-scale cryopreservation of T. gondii T-263 bradyzoites in individual vaccine doses.

Animals↗
PubMed1996

Quantification of Toxoplasma gondii bradyzoites.

A simple 2-step method to selectively quantify functional bradyzoites of Toxoplasma gondii is described. The method was developed to quantify bradyzoites produced in cell cultures that also contain tachyzoites. The selection step comprises incubation of bradyzoites and tachyzoites in 0.026% pepsin at 37 C for 30 min. This treatment kills all tachyzoites, whereas all bradyzoites survive. A modified plaque assay is then used to quantify the surviving bradyzoites. Plaque assay cultures are scored according to levels of infection that correlate with numbers of bradyzoites added to each well. The assay can detect log differences in the range of 2 x 10(0)-2 x 10(4) bradyzoites per sample. This procedure is simple to perform and provides an efficient way of comparing numbers of functional bradyzoites in multiple samples that also contain tachyzoites.

Animals↗
PubMed1993

Top-bottom and front-behind decisions on rotated objects.

Human adults decided whether a dot was nearer the top or bottom of rotated drawings of objects in a top-bottom task, and whether a dot was at the front of or behind rotated objects in a front-behind task. These two tasks were performed with the head upright and with the head tilted clockwise and counterclockwise in separate blocks of trials in order to dissociate retinal from environmental perceptual frames of reference. Response times increased approximately linearly with increasing departure from the orientation of the perceptual reference frame in both tasks and the magnitude of the effect was similar across tasks. In the head tilted conditions, the perceptual frame of reference was located midway between the environmental and retinal upright for both tasks.

Adolescent↗
PubMed1991

Salicylhydroxamic acid inhibits myeloperoxidase activity.

Salicylhydroxamic and benzohydroxamic acids were found to bind to the resting state of myeloperoxidase and inhibit ligand binding to the heme iron. An ionizable group on the enzyme with pKa = 4 affects salicylhydroxamic acid binding; binding occurs when this group is not protonated. The binding of the heme iron ligands (e.g. cyanide, nitrite, and chloride) is probably controlled by the same ionizable group. The equilibrium dissociation constant of the salicylhydroxamic acid-myeloperoxidase complex is about 2 x 10(-6) M, and the association rate constant is 7.4 x 10(6) M-1.s-1. Salicylhydroxamic acid serves as a donor to the higher oxidation state of myeloperoxidase and thereby inhibits guaiacol oxidation. Salicylhydroxamic acid was also found to bind to intestinal peroxidase and lactoperoxidase. Salicylhydroxamic acid binding to all three mammalian peroxidases was about 3 orders of magnitude stronger than benzohydroxamic acid binding. We conclude that the salicylhydroxamic and benzohydroxamic acids bind in the distal heme cavity of these peroxidases and interact with the heme ligand binding site.

Animals↗
PubMed1991

Interaction of halides with the cyanide complex of myeloperoxidase: a model for substrate binding to compound I.

EPR spectra of the low-spin cyanide complex of myeloperoxidase have been measured in the absence and presence of halide substrates; chloride, bromide and iodide. Halide-dependent spectral changes are found at acidic pH. The electronic structure of the low-spin ferric iron in cyanide complex appears to be modulated by halide binding to a protonated amino acid in the distal heme cavity. These findings suggest halide substrates can interact with ferryl oxygen in compound I during enzyme catalysis to form hypohalous acid.

Bromides↗
PubMed1990

A nuclear Overhauser effect study of the active site of myeloperoxidase. Structural similarity of the prosthetic group to that on lactoperoxidase.

The low-spin, cyanide-ligated ferric complex of the intact bovine granulocyte myeloperoxidase (MPO-CN) has been studied by proton nuclear magnetic resonance utilizing the nuclear Overhauser effect (NOE). This is the largest globular protein (approximately 1.5 x 10(5) for the intact alpha 2 beta 2 tetrameric species) for which successful NOEs have been observed without serious interference of spin diffusion, and demonstrably confirms the utility of such studies on large paramagnetic as compared to diamagnetic proteins. The 1H NMR spectrum of MPO-CN is found to have a remarkable similarity in the number, resonance pattern, and metal ion-induced relaxation properties of the resolved, hyperfine-shifted resonances to those reported earlier for the analogous complex of bovine lactoperoxidase (LPO-CN); moreover, the interproton connectivities between pairs of hyperfine-shifted proton sets, as reflected by the NOEs, are also essentially the same (Thanabal, V., and La Mar, G. N. (1989) Biochemistry 28, 7038-7044). Since the extracted prosthetic group of lactoperoxidase is a porphyrin with proposed functionalization of the 8-methylene group (Nichol, A. W., Angel, L. A., Moon, T., and Clezy, P. S. (1987) Biochem. J. 247, 147-150), we interpret the resultant similarity in 1H NMR spectral parameters for LPO-CN and MPO-CN as indicating that the prosthetic groups in MPO and LPO are very similar, and hence likely both porphyrins with a similarly functionalized periphery that allows covalent linkage to the protein matrix. The hyperfine shift pattern of the broadest resolved lines lead to their assignment to the axial histidyl imidazole side chain. Two pairs of resonances are found to have similar relaxation properties and/or dipolar as similarly shifted resonances that arise from a distal His and Arg in horseradish peroxidase (as also found in LPO-CN), and suggest that MPO also possesses these catalytically functional residues in the distal heme pocket.

Animals↗
PubMed1989

Bovine myeloperoxidase and lactoperoxidase each contain a high affinity site for calcium.

Both bovine myeloperoxidase and lactoperoxidase contain one calcium per iron with no other metal present in significant amount. Calcium is bound with high affinity and is removed upon exposure to 6 M guanidine hydrochloride/EGTA which results in precipitation of protein. Computer amino acid sequence analyses of human myeloperoxidase reveal two plausible calcium binding sites. This is the first evidence for the presence of calcium in these peroxidases.

Amino Acid Sequence↗
PubMed1989

Demonstration that spleen green hemeprotein is identical to granulocyte myeloperoxidase.

The biochemical, spectroscopic, enzymatic, and redox properties of spleen myeloperoxidase, a peroxidase formerly called "spleen green hemeprotein," and granulocyte myeloperoxidase were compared by electrophoresis, amino-terminal amino acid sequences, optical and EPR spectroscopy, steady-state enzyme kinetics, and oxidation-reduction potential. The spleen enzyme exhibits properties indistinguishable from those of the granulocyte enzyme. We conclude that the spleen enzyme is indeed identical to granulocyte myeloperoxidase.

Amino Acid Sequence↗