The quaternary structure of yeast aminopeptidase I. 1. Molecular forms and subunit size.

The smallest active form of aminopeptidase I (EC 3.4.11.1) from yeast has a molecular weight of 6.4 X 10(5). At neutral pH the active enzyme is in equilibrium with two inactive subfragments (Mr = 3.2 X 10(5) and 1.1 X 10(5)) as well as with higher aggregates (Mr greater than or equal 1.2 X 10(6)). All of these species may be dissociated to give a single type of subunits with a molecular weight of 5.3 X 10(4). It is concluded that the active enzyme is a dodecamer whereas the subfragments correspond to dimeric and hexameric forms.