Comparison of Polypeptides from Chlamydomonas segnis Adapted to Low and High Carbon Dioxide Tensions

Abstract

Chlamydomonas seynis zoospores adapted to air levels of CO 2 rather than to 5% CO 2 in air were capable of active photosynthesis at alkaline p H in the presence of a low (0.38 µM) concrntration of CO 2 . The patterns of detergent-soluble polypeptides, analyzed by two-dimensional isoelectric focusing-polyacrylamide gel electrophoresis, were compared in air- and 5% CO 2 -adapted zoospores. Both types of zoospores had at least 163 polypeptides in common, but diffrred with respect to an additional fifteen polypeptides. Of the latter, three polypeptides were specific to air-adapted zoospores. One of these was a diffuse spot (M r = 42,000) whose p I value ranged from 5.2 to 5.4. The other two polypeptides had the same p I value of approximately 7.7 and slightly different M r -values (20,000 and 22,000). In 5% CO 2 -adapted zoospores, six polypeptides varied from the aforementioned three polypeptides in either the M r -value or p I . The differences could be explained in terms of protein modification. The results suggest that the polypeptides specific to air-adapted zoospores could be linked to their photosynthetic capability at subsaturating concentrations of CO 2 .