Identified taste bud cell proliferation in the perihatching chick [published erratum appears in Chem Senses 1998 Aug;23(4):459]

Developing taste buds in the anterior mandibular floor of perihatching chicks were studied by high voltage electron microscopic autoradiography in order to identify proliferating gemmal cell types. Montaged profiles of 29 taste buds in five cases euthanized between embryonic day 21 and posthatching day 2 were analyzed after a single [3H]thymidine injection administered on embryonic day 16, 17 or 18. Results showed that dark cells comprised 55% of identified (n = 900 cells) and 62% of labeled (n = 568 cells) gemmal cells as compared with light, intermediate, basal or perigemmal bud cells. Dark cells had both a greater (P < 0.05) number of labeled cells and a greater amount of label (grains/nucleus) than the other four bud cell types, irrespective of injection day. The nuclear area (micron 2) of dark cells was not significantly larger (P > 0.05) than that of the other gemmal cell types and therefore cannot account for the greater amount for label in the dark cells. Interestingly, only dark cells showed a positive correlation (P < 0.003) between amount of label and nuclear area. Results suggest that, during the perihatching period of robust cell proliferation, dividing dark cells may give rise primarily, but not exclusively, to dark cell progeny.      

The spatial structure of the axially bound methionine in solution conformations of horse ferrocytochrome c and Pseudomonas aeruginosa ferrocytochrome c 551 by 1H NMR

A generally applicable method for the determination of the spatial structure of the heme iron-bound methionine in c-type ferrocytochromes at atomic resolution is presented. It relies primarily on measurements of nuclear Overhauser effects between the individual hydrogen atoms of the axial methionine, and between individual hydrogens of the methionine and the heme group. Four different methionine conformers, corresponding to the four possible stereospecific assignments for the methionine methylene proton resonances, are generated by a structural interpretation of the nuclear Overhauser effects with the use of an interactive computer graphics technique. A unique structure and unique stereospecific resonance assignments are then obtained by discriminating between these four conformers on the basis of van der Waals' constraints and heme ring current effects on the chemical shifts. The use of the method is illustrated with studies of horse ferrocytochrome c and Pseudomonas aeruginosa ferrocytochrome c 551. Comparison with the crystal structures shows close coincidence between the methionine conformations in solution and in single crystals of these proteins.Abbreviations NMR nuclear magnetic resonance - NOE nuclear Overhauser effect - TOE truncated driven nuclear Overhauser effect