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Fine Structure of the Cytomembranes of Nitrosocystis oceanus¹

Department of General Botany, Swiss Federal Institute of Technology, Zuricli, Switzerland
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543

ABSTRACT

Thin-sectioned, negatively stained, and freeze-etched preparations of Nitrosocystis oceanus cytomembranes were compared. The cytomembranes in freeze-etched cells were covered with 80- to 120-A particles. When cells were disrupted and differentially centrifuged, various membrane and particle fractions were obtained. Negatively stained membrane fragments from the pellet centrifuged at 3,000 x g showed 70- to 80-A stalked particles, whereas those from the pellet centrifuged at 39,000 x g exhibited a crystalline array of subunits with a 30- to 40-A periodicity. High-speed supernatant and pellet fractions centrifuged at greater than 39,000 x g contained 40- to 120-A free particles but no membranes. In chemically fixed cells, 40-A particles were found embedded in the matrix of membranes. Results suggest that the larger 80- to 120-A particles are enzyme complexes, whereas the smaller 30- to 40-A particles represent a structural protein or a lipoprotein of the membrane.

² Present address: Woods Hole Oceanographic Institution, Woods Hole, Mass.

¹ Contribution 1475 from the Woods Hole Oceanographic Institution.

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