Serine protease inactivated by freezing. Why? (fwd)

Jeff Rawlings rawlings at
Fri Feb 17 13:22:32 EST 1995

In article <9502161640.AA14681 at>,
haoxiao at cc.UManitoba.CA (Hao Xiao) wrote:

> Mr. P.A. Sansom writes:
> > My monocyte membrane extracts contain a serine protease that loses
activity on
> > freezing at -20C, even though it's very stable at 4C. If the extract is left
> > at 37C prior to assay, partial activity returns. This leads me to think that
> > 1) the proteinase is a multi-subunit enzyme that breaks up and reforms or
> > 2) an inactive form of the enzyme is converted to the active form at 37C.
> > The enzyme is inhibited by PMSF but not by trypsin/chymotrypsin inhibitors.
> > 

Many proteins are sensitive to freezing and thawing, especially when
repeated. In my experience, slow freezing the worst. You might try to
snap-freeze your samples in liquid nitrogen; also, be sure that your
freezer does not self-defrost, as this can cause repeated freezing and


Jeff Rawlings                               rawlings at

     *Internet Consulting for the Biotechnology Supplier*

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