Comparison of the chemical, physical, and survival properties of normal and Z-variant alpha-1-antitrypsins.

A procedure has been developed for the purification of Z-type alpha-1-antitrypsin (alpha-1-AT) which is rapid, gentle, and results in good yields. From 4 units (750 ml) of fresh human plasma, obtained from two individuals possessing the Pizz phenotype, 53 mg of pure Z-type alpha-1-AT was obtained. The preparation was homogeneous by the criteria of polyacrylamide gel electrophoresis, both in the presence and absence of sodium dodecyl sulfate, and by analytical ultracentrifugation. When compared to pure alpha-1-AT from plasma of individuals possessing the normal PiMM phenotype, the two proteins were indistinguishable with respect to amino acid composition, sedimentation coefficient (s20w of 3.33 for both M and Z), molecular weight (51,000 by sodium dodecyl sulfate gel electrophoresis and 47,000 by sedimentation equilibrium for both M and Z), and trypsin-combining ratio (0.91 for Z and 0.99 for M). The only difference which was observed between the variant forms of alpha-1-AT was in the carbohydrate composition. The Z-type alpha1-AT contains between 20 and 25% less carbohydrate than the M-type alpha-1-AT. Specifically, the Z-type alpha-1-AT is deficient in 1 glucosamine residue, 3 neutral sugar residues (1 mannose and 2 galactose), and 2 sialic acid residues. Although the Z-variant is deficient in sialic acid, its survival time in the serum of a rabbit was not significantly different from that of M-type alpha-1-AT.