Positive charge, negative charge. In the magnetic recombination ultrafiltration membrane experiment, when the isoelectric point of amylase is 5.5, ph is lower than the isoelectric point, amylase is positively charged, ph is higher than the isoelectric point, amylase is negatively charged. Amylase, a general term for enzymes that hydrolyze starch and glycogen, catalyzes the hydrolysis of starch slurries on fabrics.