3.4.23.31	37	-	pH 2.5-5.5, 20 h, stable	
3.4.23.31	37	-	pH 3-5, 20 h, stable	
3.4.23.31	50	-	pH 4.0, 15 min, stable below	
3.4.23.31	55	-	pH 4.8, 15 min, stable below	
3.4.23.31	60	-	pH 4.0, 15 min, 60% loss of activity	
3.4.23.31	68	-	pH 4.8, 15 min, complete loss of activity