Estimation of serum α2-macroglobulin based on the esterolytic activity of bound α-chymotrypsin

A colorimetric method to estimate α2-macroglobulin (MG) in human serum is described which is based on the capacity of MG: α-chymotrypsin complex to hydrolyze N-acetyl l-tyrosine ethyl ester in the presence of excess crude preparation of a trypsin/chymotrypsin inhibitor from redwood seed. Acetyltyrosine formed was measured using Folin's reagent (7). The method was found to be as reliable as, but at least five times more sensitive than the procedures described using trypsin and soybean trypsin inhibitor. MG level is expressed in terms of micrograms of bovine α-chymotrypsin bound. Serum from healthy males had a lower value (150.5 ± 31.9 μg/ml, n = 20) than in females (196.8 ± 40.4, n = 20). No significant difference between the levels in fasting and postprandial conditions was observed.