Zur Glykolatoxydation einzelliger Grünalgen

Summary

O₂-uptake and CO₂-release by a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris increase on addition of Na-glycolate by factors of 4–5 and 5–6, respectively (Fig. 1). In an enzyme preparation of that alga (sonification, centrifugation, precipitation with 0–30% (NH₄)₂SO₄, dialysis) activity of glycolate oxidase can be demonstrated by O₂-uptake (Fig. 2a) as well as by reduction of the artificial electron acceptor DCPIP (Fig. 2b). The same holds true for whole cells as well as equally prepared enzyme preparations of heterotrophically or autotrophically grown wildtype Chlorella vulgaris, provided the cells are cracked by a “French press” instead of a sonicator (Figs. 3a-c and 4a-c). Glyoxylate is the main reaction product (Table). Oxidation of exogenous glycolate is rapidly performed by whole cells of Scenedesmus quadricauda and of Ankistrodesmus convolutus, too, but hardly or not at all by Chlorella pyrenoidosa and Ankistrodesmus braunii. No definite influence of the level of CO₂ applied during growth is found: Chlorella vulgaris and Ankistrodesmus convolutus show a rapid oxidation of glycolate after growth under 0,03 and 1,5% CO₂ in air, whereas Chlorella pyrenoidosa and Ankistrodesmus braunii do not show an enhanced O₂-uptake on addition of glycolate after either condition (Fig. 5). Various developmental stages of Chlorella pyrenoidosa respond differently to addition of glycolate, the extra O₂-consumption varying between about 25% (mature cells) and 50–60% (young cells) of the endogenous rate (Fig. 6). It thus appears that species of unicellular green algae within the same genus have strong or weak glycolate oxidase activity and that several external factors have only a modifying effect on that enzyme.