Effects of UV‐B radiation and nitrogen starvation on enzyme activities in isolated plasma membranes of Euglena gracilis

• Circadian rhythms are characteristic of many physiological and biochemical processes in the freshwater flagellate Euglena gracilis. Earlier, we found that the rhythms of photosynthesis, phototaxis and cell shape followed the same pattern in control organisms, but were differently affected by stress such as UV‐B irradiation and nitrogen deficiency. Here we extend our studies to use isolated plasma membranes to characterize the rhythms of some plasma membrane‐bound enzymes. Also, we wanted to see whether stress‐induced changes of these rhythms could be detected at the subcellular level and possibly be coupled to the changes seen in photosynthesis, phototaxis and cell shape. The isolation of plasma membranes using aqueous polymer two‐phase partitioning was successful, as judged by the large enrichment of the plasma membrane‐marker 5′‐nucleotidase, and the difference in the polypeptide pattern compared with the microsomal fraction from which it was prepared.

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