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Genetic variation of human alpha 1-antichymotrypsin (ACT) was investigated in sera using thin-layer polyacrylamide gel isoelectric focusing (pH range 4.0-6.5) followed by immunoprinting with a monospecific anti-human ACT antibody. Sialidase-treated samples showed a microheterogeneous banding pattern which consisted of two major and several additional minor components with isoelectric points between pH 5.0 and 5.3. A population study of 200 unrelated individuals from southern Germany revealed no genetic variation. In a clinical investigation, however, we found a unique banding pattern in a female patient suffering from chronic obstructive pulmonary disease. In comparison with the monomorphic normal type the detected variant phenotype shows two additional bands that have lower intensities and are located cathodically to their major bands. Inheritance of the deficient IEF variant "ACT Bochum" was confirmed by a family study. To our knowledge this is the first genetic ACT mutant to be observed at the protein level.

In crossed immunoaffinoelectrophoresis with free concanavalin A in the first dimension, human serum alpha 1-antichymotrypsin, purified or in whole serum, exhibited four peaks in presence of 0.02 M alpha-methyl-D-glucoside added to the second-dimensional gel. alpha 1-Antichymotrypsin purified from the serum of a single healthy donor was separated by affinity chromatography into three fractions on a laboratory-prepared concanavalin A-Sepharose 4B column: a pass-through fraction, a retarded fraction and a bound fraction, eluted from the column on addition of sugar to the buffer. These three fractions were analyzed by crossed immunoaffinoelectrophoresis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing before and after desialylation. The results of electrophoresis as well as chemical analyses indicate that these microheterogeneous forms carry glycans with decreasing degrees of branching from the concanavalin A-pass-through form to the concanavalin A-bound form. This approach represents a first step towards the elucidation of the molecular basis of the microheterogeneity of alpha 1-antichymotrypsin.