Macroamylases: Differences in Activity Against Various-Size Substrates

Abstract

Hyperamylasemia caused by macroamylases can lead to the overdiagnosis of acute pancreatitis. We examined whether interference from macroamylase is less in assays that use high-molecular-weight rather than oligosaccharide substrates. We hypothesized that high-molecular-weight substrates would be sterically excluded from macroamylasemic complexes and thus would be hydrolyzed less efficiently. Eighteen macroamylasemic samples were assayed by using red-dyed amylopectin or blue-dyed starch as polysaccharide substrates or by using maltoheptaose or maltotetraose as oligosaccharide substrates. The oligosaccharide substrates gave comparable results (y = 0.81x + 83); we observed consistently lower activities for amylopectin than for maltotetraose (y = 0.32x + 38). We observed no bias among methods when nonmacroamylasemic specimens were analyzed. The mechanism of this difference was examined by adding anti-human pancreatic amylase antibodies to hyperamylasemic serum samples from patients without macroamylasemia and purified human pancreatic or salivary isoamylases. In each case, polyclonal and monoclonal antibodies lowered amylase activity more in assays with complex polysaccharides than in those with oligosaccharides. The use of high-molecular-weight substrates diminishes interference, and detection of suspected macroamylasemia may be possible through comparison of activities determined from automated methods that use different substrates.