• Applied Microscopy
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• v.22 no.1
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• pp.33-41
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• 1992

To clarify the exocytotic features in adrenal medullary aminergic cells, the authors observed rat adrenal medulla prepared by the TAGO method with transmission electron microscope. Rat adrenal medulla contains two types of aminergic cells, adrenergic and noradrenergic, as described. They were present as a group. In a single group both adrenergic and noradrenergic cells were present, but the same kind of cells showed the tendency forming small groups. Adrenergic cells were characterized with the granules having relatively electroluscent cores. These granules were relatively uniform in size, and the cores filled the granules with only thin halos. Noradrenergic cells were characterized with the granules of various size and forms. Most of the cores of these granules were generally more electron-dense than those of the adrenergic cells and only partly filled the granules without forming the halos. But, some granules were very similar in the shape and electron density as those of the adrenergic cells. Even empty-looking granules were present. Exocytotic figures with the classical omega figures were observed in both types of aminergic cells, but they were more frequent in adrenergic cells. These figures were mainly present along the plasma membranes toward the capillary. The excreted materials could be identified in the cleft of the omega figures. Apocrine-like secretory patterns but without cytoplasmic rims were identified in noradrenergic cells. Some vesicles, possibly formed from the cytoplsmic tubular systems were released. Some irregular lamellar structures of varying sizes were also observed. They looked like membranous structures sneaking through the plasma membranes. We could not, however, found any evidences of their involvement in exocytotic processes. These were present toward the capillaries and found only in the adrenergic cells. The authors conclude that the secretory processes in adrenal chromaffin cells may include not only the classical exocytotic processes but also the unusual direct secretions of granules or parts of cellular organelles. The membranous lamellar structures may indicate the remnants of excreted granules or functionally inactive excess membranes of the organelles removed from the cytoplasm.

• Toxicological Research
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• v.6 no.1
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• pp.99-107
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• 1990

Dopamine beta-hydroxylase (DBH) is a neurotransmitter biosynthetic enzyme which catalyzes the conversion of dopamine to norepinephrine. Although structural studies of the mature form of this enzyme have been extensive, the culmination of these finding had been hightly controversial and contradictory. In this study, biochemical approaches were taken to characterize the structure of mature DBH. Soluble bovine DBH was purified from aderenal medulla. Three bands of 69 kDa, 72 kDa and 75 kDa which were physically separable and similar in structure were observed by SDS-PAGE. Furthermore, gas phase sequence analysis revealed that the 72 kDa band consists of two polypeptides which are present at equimolar concentrations and differed in that one had three extra amino acids at the N-terminus. Taken together, the soluble form of DBH exist in at least four forms, three identified by SDS-PAGE, one of which consists of two polypeptides as identified by N-terminal sequence analysis. The significance of these forms and their possible biosynthetic mechanisms are discussed.

• Journal of Life Science
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• v.6 no.1
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• pp.1-5
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• 1996

Using differential hybridization, a cDNA clone was isolated fortuitously from Amaranthus viridis and sequenced. This nucleotide sequence exhibited 55.1% identity with vma6 which encodes the 36-kD subunit of the vacuolar proton transporting ATPase in Saccharmoyces cerevisiae. The predicted open reading frame encodes a protein of 221 amino acid sequence with a calculated molecular weight of 25,452 and reveals high levels of similarity with subunit D polypeptide of vacuolar H -ATP(e.g., 48.5, 52.1 and 49.3% identity to the vacuolar 36-kD chain of yeast, vacuolar 32-kD polypeptide IV of human and vacuolar 28-kD protein of bovine chromaffin granules, respectively). The hydropathy index computation revealed that this predicted protein is a peripheral protein. These results indicated that the predicted protein may play a sturctural role in the vaculor H -ATPase as does gamma subunit in V-type ATPase.