A flexible instrument control and image acquisition system for a scanning electron microscope.

We have developed an instrument control and image acquisition system for use with scanning electron microscopes. By making the system flexible over a wide range of operating voltages, scan generation and image acquisition modes can be easily accommodated to a wide range of instruments. We show the implementation of this system for use with a custom-built low-voltage scanning electron microscope.

First tests of a dipole lens for a scanning electron microscope.

We have previously shown that a dipole lens has superior properties that are particularly suited for use in a low voltage scanning electron microscope (SEM) (Tsai & Crewe, 1996). The aberrations are lower than for any other type of lens and lead to a prediction of high resolution. We describe the construction details of a microscope based on this principle and present some early results.

Molecular modeling of the interaction of diagnostic radiopharmaceuticals with receptor proteins: m2 antagonist binding to the muscarinic m2 subtype receptor.

Models of the m2 muscarinic receptor have been built and acetylcholine and an antagonist of the quinuclidinyl benzilate family docked to the putative active site. We have incorporated aspects of homology, site-directed mutagenesis studies and structure-activity studies of specific lead compounds in the construction of our receptor models with a primary focus on the structure of the binding sites. We have observed a deep pocket binding of 5-BrQNT, suggesting a plausible explanation for the observation that agonists and antagonists do not bind competitively.

Globins in nonvertebrate species: dispersal by horizontal gene transfer and evolution of the structure-function relationships.

Using a new template based on an alignment of 145 nonvertebrate globins we examined several recently determined sequences of putative globins and globin-like hemeproteins. We propose that all globins have evolved from a family of ancestral, approx. 17-kDa hemeproteins, which displayed the globin fold and functioned as redox proteins.

Alignment of 700 globin sequences: extent of amino acid substitution and its correlation with variation in volume.

Seven-hundred globin sequences, including 146 nonvertebrate sequences, were aligned on the basis of conservation of secondary structure and the avoidance of gap penalties. Of the 182 positions needed to accommodate all the globin sequences, only 84 are common to all, including the absolutely conserved PheCD1 and HisF8. The mean number of amino acid substitutions per position ranges from 8 to 13 for all globins and 5 to 9 for internal positions.