abbauen, Abbau -> degradation, so for the English sentence structure you may omit the noun degradation, and it should read: "... can only be proteolytically degraded of the contractile apparatus after irreversible cell damage (or also: cell destruction?) , or something along these lines.
Alternatively for degraded: "be proteolytically disassembled of ...."
In this context, proteolysis and disassembly of the contractile ring and degradation appear in this article ->
http://www.molbiolcell.org/cgi/reprint/16/1/193 (see page 8 of the pdf file).