Three methods compared for isoamylase separation in tissue homogenates

Using homogenates of autopsy tissue, we compared three widely available techniques for separating amylase isoenzymes: wheat-germ inhibition (WI), and electrophoresis on cellulose acetate (CA or agarose (AG). WI separated amylase into two isoforms, CA into seven (three pancreatic and four salivary), and AG into nine (five pancreatic and four salivary). CA and WI had similar isoamylase detection limits (8-10 U/L) and similar imprecision in measuring percent S-type vs P-type isoamylase (within-run SD 1-2%), and they demonstrated a linear response to added S or P isoamylase. In contrast, the AG method had higher detection limits (10-15 U/L), greater imprecision (within-run SD 3%), and showed a nonlinear response to added S or P isoamylase. We conclude that CA and WI have essentially equivalent assay attributes, superior to AG, but that CA resolves more amylase isoforms than WI.