DYNAMICS OF PSEUDOMONAS-AERUGINOSA AZURIN AND ITS CYS3SER MUTANT AT SINGLE-CRYSTAL GOLD SURFACES INVESTIGATED BY CYCLIC VOLTAMMETRY AND ATOMIC-FORCE MICROSCOPY (VOL 42, PG 2889, 1997)

Cyclic voltammetry of Pseudomonas aeruginosa azurin on polycrystalline gold is reversible (E-0 = 360 m V vs she: 50 mM ammonium acetate) but the voltammetric signals decay with time constants of about 3 x 10(-3 ) s(-1). No signal is observed for monocrystalline Au(lll). Cys3Ser az urin is electrochemically inactive on either type of gold electrode bu t shows a reversible although decaying peak (362 mV, 50 mM ammonium ac etate; decay time constant approximate to 2 x 10(-3) s(-1)) on edge-pl ane pyrolytic graphite. Ex situ and ill situ atomic force microscopy ( AFM) of the azurins on Au(1 1 1) show initially arrays of protein stru ctures of lateral 100-200 Angstrom and vertical approximate to 50 Angs trom extension. These could be individual molecular images convoluted with the tip curvature. As scanning proceeds the structures in the ex situ mode collect into large two-dimensional assemblies while the adso rbed protein in the in situ mode is largely swept into the solution, r ecovering the free Au(lll) surface. The cyclic voltammetry and AFM dat a are consistent with time dependent adsorption of the azurins on gold ria the disulphide bridge (wild-type) or free thiol group (Cys3Ser mu tant). (C) 1997 Published by Elsevier Science Ltd.