Photoinhibition of 5-aminolevulinic acid formation under GO2-free condition

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Abstract
5-Aminolevulinate accumulation in the presence of levulinate was followed in greening Chlorella protothecoides cells. Under the CO2-free condition, ALA formation was severely inhibited by 20 W/m2 white light. The inhibition was removed by CMU. Combined addition of CMU with N, N′-tetramethyl phenylenediamine plus ascorbate again caused photoinhibition of ALA formation, while the addition of CMU with dithiothreitol caused severe inhibition of ALA formation in both light and darkness. Exogenous glucose enhanced ALA formation in darkened algal celb, but not in photo- and DTT-inhibited cells. In either case, glucose seemed to be metabolized mainly by the algal cells through the glycolysis-citric acid system. It was inferred that ALA formation was suppressed at the site of, or related to, an enzyme reaction forming ALA.