Immunological discrimination of diverse forms of human alpha 1-proteinase inhibitor

The immunodiffusion cross-reactivity and competitive inhibition ELISA assays were used for immunological differentiation of latent form, cleaved form and guanidinium hydrochloride (GuHCl) induced polymer of human alpha 1-proteinase inhibitor (alpha 1-PI). Under the conditions studied, the differences between latent form and GuHCl-induced polymers of the inhibitor in terms of immunological response were estimated to amount to about 30% and differences between latent and cleaved alpha 1-PI to about 50%. The immunodiffusion and ELISA data for citrate-induced polymers suggest that in their structure the latent molecule is involved. On the basis of competitive inhibition data, we suggest that the alpha 1-PI protein polymerisation involves insertion of the reactive-site loop (RSL) into the A-sheet under mild conditions and that in the latent form of the inhibitor RSL is incompletely inserted into the A-sheet.