Showing papers by "Rod Balhorn published in 1991"
TL;DR: The results of these experiments demonstrate that the amino- and carboxy-terminal ends of the bull protamine molecule are folded inward toward the center of the molecule and are locked in place, each by a single intramolecular disulfide bridge.
Abstract: The authors have identified the disulfide cross-links in bull protamine by titrating intact bull sperm with dithiothreitol (DTT) and following the modification of each cysteine residue with tritiated iodoacetate. The derivatization of each cysteine was monitored by a combination of HPLC, peptide mapping, and protein sequencing. Analyses of total free sulfhydryls show that all seven of the bull protamine cysteines are cross-linked as disulfides in mature sperm. The first disulfide is reduced at a DTT:protamine cysteine (DTT:Cys) ratio of 0.3 and the last at a ratio of 2.0. Intra- and intermolecular disulfides were identified by correlating the reduction of specific disulfides with the dissociation of protamine from DNA in partially reduced sperm and sperm treated with N,N{prime}-ethylenedimaleimide, a bifunctional disulfide cross-linking agent. Three intermolecular and two intramolecular disulfides were identified. The results of these experiments demonstrate that the amino- and carboxy-terminal ends of the bull protamine molecule are folded inward toward the center of the molecule and are locked in place, each by a single intramolecular disulfide bridge. Three intermolecular disulfides cross-link neighboring protamine molecules around the DNA helix in such a manner that the protamines cannot be dissociated from DNA without first reducing the interprotamine disulfides.
74 citations
Journal Article•
TL;DR: These studies provide the first evidence that tunneling microscopy can be used to discriminate between purines and pyramidines.
Abstract: The scanning tunneling microscope has been used to obtain images of DNA that reveal its major and minor grooves and the direction of helical coiling, but sufficient resolution has not yet been achieved to identify its bases. To determine if this technology is capable of identifying individual DNA bases, we have examined the molecular arrangements of adenine and thymine attached to the basal plane of highly oriented pyrolytic graphite. Both molecules form highly organized lattices following deposition on heated graphite. Lattice dimensions, structural periodicities, and the epitaxy of adenine and thymine molecules with respect to the basal plane of graphite have been determined. Images of these molecules at atomic resolution reveal that the aromatic regions are strongly detected in both molecules while the various side-groups are not well-resolved. These studies provide the first evidence that tunneling microscopy can be used to discriminate between purines and pyramidines.
27 citations
TL;DR: The results show that alcohol preservation does not alter the primary structure of the two sperm nuclear proteins and that the preservation of mammalian reproductive organs in alcohol is a viable alternative to freezing tissues collected in the field.
Abstract: Protamines 1 and 2 have been isolated from the sperm of frozen and isopropanol preserved Syrian hamster (Mesocricetus auratus) epididymides and analyzed by gel electrophoresis, high-performance liquid chromatography (HPLC), and amino acid analysis and sequencing. The results show that alcohol preservation does not alter the primary structure of the two sperm nuclear proteins and that the preservation of mammalian reproductive organs in alcohol is a viable alternative to freezing tissues collected in the field. Sperm were isolated from tissues fixed in isopropanol for as long as 7 months without detectable adverse effects on either the isolation of sperm or the primary structure of the protamines.
7 citations
TL;DR: In this paper, images of three different synthetic DNAs have been obtained by scanning tunneling microscopy (STM) following their deposition on graphite using a voltaic pulse. DNA applied to the STM tip is desorbed during a 4 V/10 μs pulse and deposited intact onto the surface of highly oriented pyrolytic graphite.
Abstract: Images of three different synthetic DNAs have been obtained by scanning tunneling microscopy (STM) following their deposition on graphite using a voltaic pulse. DNA applied to the STM tip is desorbed during a 4 V/10 μs pulse and deposited intact onto the surface of highly oriented pyrolytic graphite. Images of 22, 47, and 100 base‐pair molecules show that deposition occurs in close proximity to the tunneling tip and that the molecules appear to deposit singly or in highly oriented groups.
7 citations