MOLECULAR-PROPERTIES OF AMINOPEPTIDASE EY AS A ZINC-METALLOENZYME

1. Aminopeptidase Ey from hen's egg yolk contains 1.0 g atom of zinc/m ol of a subunit having molecular weight of 150 kDa. The inactive, Zn2-free apoenzyme was reactivated by Co2+, Mn2+, Ca2+, Cd2+, Cu2+ and Ni 2+ in addition to Zn2+, whereas Mg2+ and Fe2+ were ineffective. 2. The enzymatical properties of reconstituted enzymes, except for Zn2+-reco nstituted enzyme, differed from native enzyme. The values for the acti vation energy were calculated by aminopeptidase Ey and Co2+-reconstitu ted enzyme. 3. The isoelectric point of the enzyme was about 2.8 as de termined by isoelectric focusing. An asialo form of the enzyme, obtain ed by treatment with Arthrobacter sialidase, had an isoelectric point of 4.4. 4. The amino terminal sequence of aminopeptidase Ey was determ ined to be acyl-Xaa-Xaa-Pro-Glu-Ala-Ala-Ser-Leu-Pro-Gly. There was no identity with any known sequences of aminopeptidase.