IMAGING PROTEINS BY STM IN AIR

Sonia Antoranz Contera and Hiroshi Iwasaki

The Institute of Scientific and Industrial Research (ISIR), Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.

Due to its very high resolution and capabilities we have applied STM in air to the study of proteins, especially two of them: pseudoazurin and apo-pseudoazurin. Pseudoazurin (13kDa) is a blue redox metalloprotein that contains a copper atom, apo-pseudoazurin is pseudoazurin without the copper. Both proteins adsorbed onto a Au (111) surface are visible to STM individually and in layers and multilayers, in currents from about 55pA to 500pA and tunnelling bias from about -2V to +2V. The size of individual units is about 6nm. Their height varies with the voltage polarity, being higher at negative bias. The bias also affects their shape. High voltage pulses (~ ﾅ}4V) can move and orient the proteins individually and within layers. Larger proteins such as Ferritin could also be imaged.

Acknowledgement: Specimens were provided by Prof. S. Suzuki at Osaka University. We thank Prof. K. Tanizawa for fruitful discussions.