According to an old Worthington Biochemicals catalog description of
peroxidase, sodium azide is an irreversible inhibitor of HRP.  We routinely
use it up to the washes following secondary antibody incubations, to
supress endogenous peroxidative activity and growth of biologicals
(bacteria, fungi) during long incubations.  This can actually make it
unnecessary to use processing steps designed to block tissue peroxidative
activity, such as peroxide and/or methanol incubations.  Just don't forget
to switch to non-azide buffer before and after any incubations where HRP
reagents are used.  It also works to block residual HRP activity after
visualizing one target so that another HRP chromogen can be used to
double-label a second target with a different colored reaction product.  It
should go without saying of course, that one also needs to pay close
attention to the safety requirements for sodium azide.

In response to: 
Date: 8 Aug 2002 15:17:55 -0500
From: Jackie.O'Connor@abbott.com
Subject: NaN3 in BSA
OK - is there a reason I should think 0.1% NaN3 in 0.3% BSA is inhibiting the
enzyme activity of horseradish peroxidase when used as a diluent for CD31 and
the GAR secondary I'm using?  Just tell me - I can take it.  Thanks.