N-terminal domain of pepsin as a model for retroviral dimeric aspartyl protease

Autolysis of porcine pepsin at pH 4 affords a derivative possessing intrinsic proteolytic activity. This derivative was isolated by alumina pseudo-affinity chromatography and gel-filtration and was found to result from the tight association of two identical molecules, 135 amino acids long, emerging from the N-terminal domain of pepsin. This finding emphasizes a similarity with the only aspartyl-proteases known to act as dimers, the retroviral proteases.