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A copper-containing protein, plastocyanin from poplar leaves, has been crystallized in the oxidized (i.e Cu(II)) state. The deep blue crystals are rhombic prisms with space group P212121 and cell dimensions a=29·6A, b=46·9A, c=57·6 A. The molecular weight is 10,500. There are four molecules of protein in the unit cell, and hence there is one molecule in the asymmetric unit.

A basic protein with a molecular weight of approximately 10,100 and having a single atom of Type I copper has been isolated from cucumber seedlings. The oxidized, cupric, form of the protein has been crystallized as thin olive-green plates with space group P 2 1 2 1 2 1 and cell dimensions a = 30.8 A, b = 45.6 A and c = 66.6 A. There is one protein molecule per asymmetric unit.

An acid protease has been purified 470-fold from mung bean seedlings. With bovine serum albumin as substrate, the enzyme showed an optimum at pH 3·6 and at 45° or incubation for 1 hr. The enzyme was relatively stable after incubation for 20 hr between pH 3.·0 and pH 6·0 but lost activity on incubation at 15° for 15 min at pH 6°8.