Journal articles

Atomic force microscopy has been used to investigate changes in the plasma membrane overlying the head region of mammalian spermatozoa (bull, boar, ram, goat, stallion, mouse, and monkey) during post-testicular development, after ejaculation, and after exocytosis of the acrosomal vesicle. On ejaculated ram, bull, boar, and goat spermatozoa the postacrosomal plasma membrane has a more irregular surface than that covering the acrosome. The equatorial segment, by contrast, is relatively smooth except for an unusual semicircular substructure within it that has a coarse uneven appearance.

Atomic force microscopy (AFM) has been used to examine perturbations in the tertiary structure of DNA induced by the binding of ditercalinium, a DNA bis-intercalator with strong anti-tumour properties. We report AFM images of plasmid DNA of both circular and linearised forms showing a difference in the formation of supercoils and plectonemic coils caused at least in part by alterations in the superhelical stress upon bis-intercalation.

Evidence is growing that biological membranes contain lipid microdomains or "rafts" that may be involved in processes such as cellular signaling and protein trafficking. In this study, we have used atomic force microscopy to examine the behavior of rafts in supported lipid bilayers. We show that bilayers composed of equimolar dioleoylphosphatidylcholine and sphingomyelin spontaneously form rafts, which are detectable as raised features.

1. Streptavidin is a 60-kDa tetramer which binds four molecules of biotin with extremely high affinity (K(A) approximately 10(14) M(-1)). We have used atomic force microscopy (AFM) to visualize this ligand-protein interaction directly. 2. Biotin was tagged with a short (152-basepair; 50-nm) DNA rod and incubated with streptavidin. The resulting complexes were then imaged by AFM. The molecular volume of streptavidin calculated from the dimensions of the protein particles (105+/-3 nm(3)) was in close agreement with the value calculated from its molecular mass (114 nm(3)).

Bacterial type I restriction/modification systems are capable of performing multiple actions in response to the methylation pattern on their DNA recognition sequences. The enzymes making up these systems serve to protect the bacterial cells against viral infection by binding to their recognition sequences on the invading DNA and degrading it after extensive ATP-driven translocation. DNA cleavage has been thought to occur as the result of a collision between two translocating enzyme complexes.

Renal physiologists focus on events that take place on and around the surfaces of cells. Various techniques have been developed that follow transport functions at the molecular level, but until recently none of these techniques has been capable of making the behavior of molecular structures visible under physiological conditions. This apparent gap may be filled in the future by the application of atomic force microscopy. This technique produces an image not by optical means, but by "feeling" its way across a surface.

The origin of contrast in atomic force microscopy (AFM) lies in the probe's response to forces between itself and the sample. These forces most commonly result from changes in height as the tip is scanned over the surface, but can also originate in properties inherent in the sample. These have been exploited as further means of contrast and have spawned an array of similar imaging techniques, such as chemical force microscopy, magnetic force microscopy, and frictional force microscopy.