Iodinated Proteins

[10525kfb@ibm.cl.msu.edu (Kristin Erickson)]

Hello, Radsafers:

In response to the iodinated protein discussion, there are a few
considerations that have not been mentioned.  I do have  personal
experience, having been in research before health physics.

Once the iodine is bound to protein, it is stable for a period of time, at
most a few weeks, depending on the particular protein.  It is related to
molecular weight of the protein, among other factors.  However, after a
period of time, the protein is broken down by the radiation, liberating
free iodine once again.  For this reason, workers should be cautious in
handling old iodinated compounds.  We require workers to handle wastes from
iodinations in the fume hoods.

Another factor to consider with these iodinated proteins is the efficiency
of the chromatography separation.  Some chromatography columns are better
than others, some proteins separated better than others, etc.  Indeed, if
making their own columns, as most  iodination labs do, the pouring of the
column, the protein coating agent, the proper mixing of the buffers, and
the speed of coating the column all affect the efficiency of separating
free from bound iodine. Obviously, a less efficient separation is an
increased amount of free iodine in the bound fractions.

One of our radiation safety committee members used to do 100 millicurie
iodinations, where this efficiency was a significant factor in risk of
intake.  He actually measured free iodine release from capped 12 x 75 test
tubes containing fractions of 125I-bound proteins.  There is some amount of
free iodine in even the very best of separations.

In typical uses, though, this is not a problem.  We conduct thyroid scans
on all workers iodinating or observing iodinations.  We seldom see any
uptake, and when we do, it is typically a new worker who did not follow the
iodination precautions.  Only if the users are iodinating the very high
quantities would this be a problem.

The more common problems in intakes are due to

 -Not handling waste in the fume hood
 -Not capping the fraction tubes before moving from the hood
 -Disposing of waste in containers outside the hood
 -Having a very cluttered hood; blocks the air flow
 -Not venting the stock Na125I vial prior to withdrawing the aliquot for
iodination (a 16 gauge cannula adaptor needle makes an excellent
conduit for venting and then allowing the very tiny Hamilton syringe needle
to enter the vial)
  -Last, but not least, carelessness


Hope this helps.  Just some pointers learned over the years.

Have a great weekend!  We are steaming like clams here in Michigan!

Kristin

All comments herein contained are my own opinions and/or experiences and
are not necessarily those of my employer or institution.

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Kristin Erickson, Radiation Safety Officer
Office of Radiation, Chemical and Biological Safety
C124 Research Complex-Eng.
Michigan State University
East Lansing, Michigan 48824
Telephone: (517) 355-5008   Fax: (517)353-4871   Email: 10525kfb@msu.edu
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