Abstract
Immunochemical labeling was used to study the subcellular distribution of cytochrome oxidase, a respiratory protein, in Trichodesmium thiebautii. The protein was found associated with both cytoplasmic and thylakoid membranes. About a sixfold variation in the protein content (gold particle count) was found among Trichodesmium cells within a single colony. Double labeling was performed with cytochrome oxidase and nitrogenase antisera. Regression analysis of gold particle counts per unit of cell area of cytochrome oxidase and nitrogenase showed a positive correlation (r = 0.911); cells with higher nitrogenase levels also had higher levels of cytochrome oxidase. The parallel expression of two proteins suggests that respiratory oxygen uptake may be involved in nitrogenase protection (respiratory protection) in Trichodesmium spp.