The pH profile of hemoglobinolytic activity in the I. ricinus gut tissue extracts. Gut tissue was dissected from partially engorged tick females (the 5-th day of feeding), washed from the gut contents and extracted. Fluorescently labeled AMC-hemoglobin was digested in vitro with gut extract at various pH values. The relative rate of degradation of the substrate was determined using the measurement of fluorescence in a continuous hemoglobinolytic assay. The error bars indicate standard deviations of the mean of triplicates.