Allelic variants of alpha-1 antitrypsin carry alphabetical designations, from A to Z, with A representing the fastest variant in a zone electrophoretic separation, and Z the slowest. Two variants, in particular, are associated with the above diseases, the S and the Z allelic products. Both of these exhibit amino acid substitutions at sites that are normally glycosylated. All variants are expressed as allelic co-dominants. Unfortunately, zone electrophoresis is not a sensitive enough technique to allow phenotyping, and subsequent genetic counseling.
Proteins migrate to their isoelectric points where they form tight bands.
IEF, using a narrow pH gradient, gives rise to an eight band pattern for each allelic product. In theory, one cannot distinguish between an individual who is homozygous for an allelic product versus one who has inherited a null allele. However, in practice, null alleles are so rare that this is not a significant problem. Isoelectric focusing is a technique capable of obtaining the greatest resolution of a protein mixture. Polyampholines are small peptides, which arrange themselves according to isoelectric point when exposed to an electric field.