Direct observation of the transition from calcite to aragonite growth as induced by abalone shell proteins.

The mixture of EDTA-soluble proteins found in abalone nacre are known to cause the nucleation and growth of aragonite on calcite seed crystals in supersaturated solutions of calcium carbonate. Past atomic force microscope studies of the interaction of these proteins with calcite crystals did not observe this transition because no information about the crystal polymorph on the surface was obtained. Here we have used the atomic force microscope to directly observe changes in the atomic lattice on a calcite seed crystal after the introduction of abalone shell proteins. The observed changes are consistent with a transition to (001) aragonite growth on a (1014) calcite surface.

Recent highlights from atomic force microscopy of DNA.

Abstract Seven recent highlights are presented from atomic force microscopy (AFM) of DNA in this lab. The first two involve advances in the observation of enzymatic reactions in near-physiological solutions. E. coli RNA polymerase was observed to process along its DNA template in a series of time-lapse images [S. Kasas, et al., Biochemistry 36, 461 (1997)], and a new small-cantilever atomic force microscope (AFM) imaged DNA degradation by DNase I at rates as fast as two seconds per image. The next five highlights involve structural observations of DNA and DNA-protein complexes, including DNA condensed for gene delivery, sequence-dependent DNA condensation, an AFM assay for RNA polymerase, and AFM evidence for a yeast kinetochore complex that may be involved in holding together sister chromatids during cell division.

Modification of calcite crystal growth by abalone shell proteins: an atomic force microscope study.

A family of soluble proteins from the shell of Haliotis rufescens was introduced over a growing calcite crystal being scanned in situ by an atomic force microscope (AFM). Atomic step edges on the crystal surface were altered in shape and speed of growth by the proteins. Proteins attached nonuniformly to the surface, indicating different interactions with crystallographically different step edges. The observed changes were consistent with the habit modification induced by this family of proteins, as previously observed by optical microscopy. To facilitate further studies in this area, AFM techniques and certain AFM imaging artifacts are discussed in detail.