First Direct Observation of Elementary Steps on the Surfaces of Glucose Isomerase Crystals under High Pressure

Abstract

We have succeeded in the first direct observation under high pressure of the elementary steps (7.2 nm high) on {011} faces of glucose isomerase (GI) crystals, by using a laser confocal microscope combined with a differential interference contrast microscope (LCM-DIM) and a specially designed high-pressure vessel with a sapphire window of 1 mm thickness. The images of elementary steps taken under 50 MPa exhibited a sufficiently high contrast level for subsequent studies of crystal growth. By in situ observations, we directly confirmed that, irrespective of pressure, {011} faces of GI crystals grew by two-dimensional (2D) nucleation growth of the polynucleation type, and that pressure did not affect growth morphology. We measured the solubility of GI crystals under high pressure by observing in situ the growth and dissolution of elementary steps and ridges on the crystals. The resulting solubility curve exhibited much higher precision than those determined by interferometry, and revealed a significant decrease in solubility with increasing pressure. We also measured the 2D nucleation rates of 2D islands and the velocities of elementary steps under high pressure.