The lead phosphate precipitation method showed the reaction product of acid phosphatase (which reflects the presence of the enzyme glycoprotein) in peripheral cytoplasmic vesicles in the ascomycetous fungus Claviceps purpurea. The product appeared to diffuse from these vesicles (diameter 100-200 nm) towards the cell wall, usually to its sites covered by the capsular fibres exhibiting also acid phosphatase activity. This observation of diffusion of secretory glycoprotein in the cytoplasmic matrix and its orientation to the plasmalemma and capsular fibrils suggests an alternative to the well-described secretory mechanism of transport and exocytosis of glycoproteins via membrane-bound transport conveyors fusing with the cell membrane. It confirms and enlarges our previous finding of the reaction product of acid phosphatase performed by ultrastructural cytochemistry in vacuoles (lysosomes), in the growing cell septum, in cytoplasmic vesicles and in the fibres of the external capsule.

• MeSH
• Cell Membrane metabolism   MeSH
• Claviceps enzymology   ultrastructure   MeSH
• Cytoplasm metabolism   MeSH
• Cytoplasmic Vesicles enzymology   ultrastructure   MeSH
• Diffusion MeSH
• Acid Phosphatase metabolism   MeSH
• Lysosomes enzymology   ultrastructure   MeSH
• Vacuoles enzymology   ultrastructure   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acid Phosphatase MeSH

Under electron microscope, the matrix of sectioned mitochondria exhibits ribosomes and an oval, electron-transparent zone which is devoid of ribosomes and is named chondriolite. Fine fibers or clumps of an electron-dense material appeared in this zone after several fixation and contrasting steps and were identified with mitochondrial DNA by cytologists. To verify this assumption, we labeled DNA by a monoclonal antibody and a secondary antibody coupled to immunogold. The label was observed in the nucleus and in the chondriolite zone of sectioned mitochondria. Because the ultrastructure of chondriolites resembles that of nucleoids of prokaryotes, we suggest the term mitochondrial nucleoid for the zone of mitochondrial matrix devoid of ribosomes and containing DNA.

• MeSH
• Aspartate Carbamoyltransferase analysis   MeSH
• DNA, Fungal analysis   MeSH
• Microscopy, Immunoelectron methods   MeSH
• Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) analysis   MeSH
• DNA, Mitochondrial analysis   MeSH
• Mitochondria chemistry   ultrastructure   MeSH
• Multienzyme Complexes analysis   MeSH
• Saccharomyces cerevisiae Proteins * MeSH
• Saccharomyces cerevisiae chemistry   genetics   ultrastructure   MeSH
• Submitochondrial Particles chemistry   ultrastructure   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Aspartate Carbamoyltransferase MeSH
• DNA, Fungal MeSH
• Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) MeSH
• DNA, Mitochondrial MeSH
• Multienzyme Complexes MeSH
• Saccharomyces cerevisiae Proteins * MeSH
• URA2 protein, S cerevisiae MeSH Browser

Exponential culture of a Saccharomyces cerevisiae strain with overexpressed aspartate carbamoyltransferase activity (ACTase) was chilled in ice and fractionated by centrifugal elutriation to several cell populations of increasing cell mass. The enzyme activity which belongs to the pyrimidine biosynthesis pathway, was detected in situ by a specific ultracytochemical reaction: the ACTase byproduct, monophosphate, was precipitated by cerium ions to cerium phosphate. During the outgrowth of nonbudding daughter cells (zero cells) the label appeared first in membranes of nuclear envelope and of mitochondria. In larger zero cells, this label appeared also in the endoplasmic reticulum, microvesicles and plasmalemma. In budding mother cells, the label was conspicuous in the whole cell-membrane complex. In most aged cells the ACTase activity was not detectable. The presence of ACTase activity in membranes of compartments conveying glycoproteins via the secretory pathway remains to be explained. To confirm the in situ detection of ACTase activity in membranes, we assayed the enzyme activity in both the 10,000 g sediment and supernatant prepared from yeast homogenate precentrifuged at 3000 g. From 23 to 43% of ACTase activity was detected in the sediments including membranes of wild-type and ACTase-overexpressing strains.

• MeSH
• Aspartate Carbamoyltransferase isolation & purification   MeSH
• Cell Membrane enzymology   ultrastructure   MeSH
• Cell Division MeSH
• Cell Fractionation MeSH
• Intracellular Membranes enzymology   ultrastructure   MeSH
• Cell Compartmentation MeSH
• Organelles enzymology   ultrastructure   MeSH
• Saccharomyces cerevisiae enzymology   growth & development   ultrastructure   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Aspartate Carbamoyltransferase MeSH