EndoS is hydrolyzed by SpeB. Panel A, analysis of SpeB-hydrolysis of EndoS during growth of the wild type AP1 (lanes A and B), the SpeB mutant AL1 (lane C and D), and the EndoS mutant MC14 (lanes E and F) with antiserum against EndoS and SpeB. Presence or absence of DTT during growth is indicated under the lower panel. Arrows to the right indicate the positions of full-length EndoS (FL), the zymogen (Z) and proteinase (P) forms of SpeB. Panel B, rEndoS incubated with increasing amounts of SpeB (lanes A-E) or thermolysin (lane F) as indicated and analyzed by SDS-PAGE. Arrows to the right indicate the positions of the 46- and 62-kDa forms of EndoS, SpeB, and thermolysin. Panel C, densitometric analysis of whole lanes A-E (excluding SpeB) in panel B. Values are presented as area under the curve in pixels.