Isoenzymes of pyruvate kinase in a chlorophyll-free Chlorella mutant and their blue-light-mediated interconversion [algae]
1981
Ruyters, G. (Bielefeld Univ. (Germany, F.R.). Fakultaet fuer Biologie)
Dark-grown resting cells of the chlorophyll-free, carotenoid-containing mutant no.20 of the green alga Chlorella vulgaris contain two isoenzymes of pyruvate kinase (PK; EC 2.7.1.40). These isoenzymes differ in chromatographic behaviour on anion exchange columns as well as in the affinities to their substrate PEP: the S(0.5) (PEP) for PK(1) is about 3 mM, that for PK(2) approximately 0.7 mM. Blue irradiation of these Chlorella cells causes a decrease in PK(1) and an increase in PK(2), thereby leading to a higher PEP affinity of the enzyme. This blue-light-mediated decrease in S(0.5) occurs also in the presence of protein synthesis inhibitors so that it appears to be the result of an interconversion of PK(1) to PK(2). Since our data also confirm the enhancing effect of blue light on total PK activity - reported earlier for the enzyme in crude cell extracts - the postulated dual effect of blue light on pyruvate kinase of PK(1) to PK(2), and second a de novo synthesis of enzyme protein, probably that of PK(2).
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