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Human liver mRNA isolated from subjects phenotyped as homozygous PiMM or PiZZ alpha 1-antitrypsin, was translated in a reticulocyte cell-free system, and alpha 1-antitrypsin identified by immunoprecipitation. In the presence of dog pancreas membranes the translated alpha 1-antitrypsin appeared as a larger product. Treatment with endo-beta-N-glucosaminidase yielded a protein smaller than the reticulocyte translated product, presumably due to removal of the N-terminal signal sequence by membranes and sugar residues by endo-beta-N-glucosaminidase. Quantitation of alpha 1-antitrypsin translated from PiMM and PiZZ livers suggests that both mRNA species were present at the same cellular concentration, and that processing to the core glycosylation stage proceeded at identical rates.

Microinjection of human liver mRNA from a patient homozygous for alpha 1-antitrypsin deficiency (PiZZ) into Xenopus oocytes led to a 2--10-fold increase in lysosomal activity. Stimulation of lysosomal activity was not observed when mRNA from a normal human liver (alpha 1-antitrypsin PiMM), or water was injected into the oocyte. This lysosomal activity was oocyte derived and was not due to translation products of the human liver mRNA. Thus a protein that accumulates intracellularly in the secretory pathway is capable of stimulating lysosomal activity.

mRNA was prepared from autopsy liver samples from a homozygote for alpha 1-antitrypsin deficiency (PiZZ) and from a normal (PiMM) subject. Both preparations gave equivalent synthesis of alpha 1-antitrypsin in a wheat germ cell-free system. This suggests that the deficiency of plasma alpha 1-antitrypsin associated with the Z variant is due to a failure of processing and secretion of the protein rather than of its synthesis. It is likely that it is the resultant intracellular accumulation of the Z protein rather than a deficiency of protease inhibitor that is the primary cause of the liver pathology associated with this variant.

Injection of equivalent amounts of normal (PiMM) or abnormal (PiZZ) alpha 1-antitrypsin mRNA into Xenopus oocytes resulted in secretion of both the normal and abnormal alpha 1-antitrypsin. A much lower proportion of the abnormal protein was secreted, and the Z alpha 1-antitrypsin that was not secreted accumulated within the cell in a high-mannose form. The time taken for secretion of the normal and abnormal proteins was identical. Both the secreted and intracellular alpha 1-antitrypsin synthesized by oocytes were functionally active.