Involvement of thylakoid membranes in supramolecular organisation of Calvin cycle enzymes in Anacystis nidulans

Abstract

The cells of unicellular photosynthetic cyanobacterium Anacystis nidulans were permeated with lysozyme, toluene, toluene-triton, toluene-triton-lysozyme. Transmission electron microscopy of semi-thin sections (500 nm) using TEM at 160 kV showed that cells permeated with only lysozyme or toluene showed the typical concentric arrangement of thylakoid membranes. However, when toluene-treated cells were further treated with triton and lysozyme the thylakoid membranes were disrupted. Sequential reactions of Calvin cycle were studied in the differentially permeated cells in vivo, using various intermediates such as 3-PGA, GA-3-P, FDP, SDP, R-5-P, RuBP and cofactors like ATP, NADPH depending on the requirement. RuBP and R-5-P+ATP dependent activities could be observed in all types of permeated cells. Sequential reactions of the entire Calvin cycle using 3-PGA could be detected in the cells that had retained the internal organisation of the thylakoid membranes after permeation and were lost on disruption of this organisation. Light dependent CO₂ fixation could be detected only in the cells permeated with lysozyme. This activity was abolished in the cells after treatment with toluene. The results suggested that the integrity of thylakoid membranes may be essential for the organisation of sequential enzymes of the Calvin cycle in vivo and facilitate their functioning.