Environmental and Molecular Mutagenesis - Legacy Tobacco ...

484
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IMUrID RE.VEFtSION OF A SPONfAt~OUS POINT NATPATICN WITHIN THE CHINESE HAFISTFR HPRT
GENE~ Yrz~ ~~ 1
B J F Rossiter ~DCMuzny , C T Caskey1 and r( ~, 2 Inst 1 for Molecular
Genetics, Baylor College of Medicine, Houston :Texas 77030, USA, jDept of Biochem
Genetics,Paterson Institute for Cancer Research, Manchester .
Spontaneous HPRT mutants can revert spontaneously at different frequencies by
anplification, point autation at the site of the original mutation or at a second
site . HPRT mutants can also revert at widely different frequencies on exosure to
alkane sulptnnates or alkyl nitrosaueas . The lowest frequencies (5 x 10 50pghnl
1rIDtu1 were observed in mutants e .g . TG15_arith normal amounts of nozmal sized HPRT
mRm . Two other mutants with no detectable HPRT s04A revert at a tenfold higher
frequency . A cDNA library was made fzan 4G15 in gtlO and a full length clone
isolated after screening with HPRT cDNA. Sequencing revealed an A -> G transition
which results in the substitution of glycine for aspartic acid at position 134 .
Allele specific screening of in vitro amplified DNA frem wild-type cells, TG15 and
four independent M induced revertant clones showed that all the had regained the
wild-type sequence . Thus the point mutation in the TG15 is responsible for
inactivation of the HPAT enzyme . Amino acid 134 is thought to lie within the
catalytic domain . These results and those in which a truncated form of the E coli
ada gene transfected and expressed in TG15 (FCa and Margison, Mutagenesis 3, 409,
1988) Eeduced the induced revertant frequency are consistent with the conclusion
that 0 nmethylguanine is the promutagenic lesion and reversion is due to a point
mutation at the site of the original lesion .
485
BETA-CA~~TENE IN AQUEOUS DISPERSION AS A SCAVENGER OF
H~O2/CU /ASCORBATE GENERATED FREE RADICALS :EFFECTS OF PARTIAL
PRESSURES OF OXYGEN . EJ .Rousseaus, AJ . Davison & M.P. Rosin . Bioenergetics Research
Lab . Faculty of Applied Sciences, School of Kinesiology, Simon Fraser University, Burnaby, B.C .
V5A 1S6 and BC Cancer Research Centre, 601 W 10th Ave ., Vancouver, B .C. VSZ 1L3
We report on the antioxidant capacities of beta-carotene In aqueous dispersion as a
scavenger of hydroxyl radicals under varying partial ressures of oxygen . Hydroxyl radicals
(generated by hydrogen peroxide In the presence of oopper and asoorbate) pxid¢ed betacarotene
resulting in a loss of absorbance at 460nm . A mixture of 0 .1mM Cu +, 0.5mM
ascorbate, and 2.5mM H2050 iIn Hepes buffer at pH 7.4 and 25~, was used, oxidizing 2 .76ug
beta-carotene/min . Each ofthe active ingredients was essential. If any were omitted, the rate of
bleaching of beta-carotene decreased by more than 20% . This system was studied under high
oxygen(62%), normoxic(21%), and low oxygen(5%), each with four concentrations of H 02
(2 .5, 5, 7 .5, and 1omM) . Rates of bleaching of beta-carotene under 20% oxygen were a~f
average of 15% and 30% higher than 62% and 5% pressures of oxygen . Thus beta-carotene is
at its most efficient as an antioxidant at intermediate partial pressures of oxygen, In partial
agreement with other workers who have shown enhanced protection at p02 below ambient
levels. Beta-carotene is capable of scavenging hydroxyl radicals . The ability of beta-carotene to
function as an antioxidant against free radicals could help define a mechanism by which betacarotene
acts a chemopreventative agent .
486
TRADESCANTIA-MICRONUCLEUS BIOASSAY ON CI~STOGENICITY OB WASTEWATER AN{~ I~i SITU AIR
MONITORING, E . F . Ruia1, E . R . Valtierra , S. U . Lecona , and T . H . Ma , 'Centro de
Estudios Academ~cos sobre Contaminacion Ambientl, IInivereidad Autonoma de Queretaro,
QRO, Mexico, Institute for Environmental Management and Department of Biological
Sciences, Western Illinois University, Macomb, IL (USA)
Tradescantia-Micronucleus (Trad-MCN) bioassay is known to be a highly sensitive short
term test for clastogenioity of water directly without concentration and on site
monitoring of clastogenicity of air pollutants without collecting air condensates .
Results can be obtained within 36 - 48 hr . Trad-MCN bioassay was applied to
wastewater samples collected from the canal at a point about 8 kilometers down stream
of the industrial zone of Queretaro City , Mexico . Four liters of water samples
were collected monthly for tests in the year of 1987 and part of the years of of
1986 and 1988, for the clastogenicity of the water through the rainy and dry seasons .
On site monitoring of the clastogenicity of the air with Trad-MCN test was done at
three locations in the city . The clastogenicity which was reflected by the
frequencies of micronuclei in the meiotic pollen mother cells was always higher in the
wastewater treated groups than the negative control group group using tapwater . When
the fluctuated MCN frequencies were compared with the monthly rainfall records, the
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts 167
Notes