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GUIDELINES
FOR S-35 METHIONINE LABELING
Methionine and cysteine-methionine
compounds are widely used in research. At room temperature and above,
small amounts of volatile S-35 decomposition products may be generated.
Prior to opening and before thawing, the
manufacturers recommend venting the stock vials in a chemical fume hood.
Pierce the septum with a cotton plugged needle or charcoal trap, taking
care not to come into contact with the contents. Thaw at room temperature
or in a 37o C water bath. Remove the needle or trap and discard
in the radioactive waste sharps container.
When used for in-vivo labeling
experiments, the following measures should be taken to reduce the levels
of contamination that occur in water baths and incubators.
Water baths:
1. Periodically assay the water in the
bath for radioactive content. Count an aliquot of the bath water in a
scintillation counter. Discard in the Rad sink if S-35 is detected.
2. When removing your samples, be careful
not to drip water onto counters and floors.
Incubators:
1. Place a shallow pan of activated
charcoal or granulated carbon in the incubator at the same time as your
cells. This will trap volatile S-35. Survey the charcoal with a GM
survey meter and discard the charcoal as radioactive waste if any
reading is detected. Note: the high humidity within the incubator will
tend to reduce its effectiveness over time.
NOTE:
Several researchers report successful contamination control using
plastic containers as mini-containments within the incubator. Two
variations that are successfully used are:
A) Placement of the culture dishes
inside a larger (say 14" x 10" x 3") plastic
container with tight fitting lid. If the atmosphere is allowed to
equilibrate before the lid goes on, the CO2 trapped
within is adequate for several days of incubation time. The
containers should be opened in a chemical fume hood.
B) Placement of the culture dishes along
with a pan of charcoal inside a larger plastic container with
perforations in the lid. This allows full gas circulation but tends
to localize the volatile S-35.
Periodically assay the water in the
incubator drip pan for radioactive content. Count an aliquot of the bath
water in a scintillation counter. Discard in the Rad sink if S-35 is
detected.
Take a smear of the incubator surfaces
most likely to become contaminated. Pay special attention to the inner
door, the door gasket, and the shelves. Decontaminate as necessary.
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