Abstract
Chlorophyllide a oxygenase (CAO) is a rieske-type monooxygenase that catalyzes conversion of chlorophyll a to chlorophyll b. CAO protein consists of three domains, namely, A, B and C domains, and A-domain alone is involved in the regulatory mechanism of the CAO protein level. In order to identify the amino acids which are involved in the regulation, we made 1000 mutants in which amino acids of the A domain were mutagenized by the random mutagenesis technique, and analyzed which amino acids were involved in the regulatory mechanism. We found that amino acid substitution of specific 7 residues moderately impaired the regulatory mechanism. Subsequently, we deleted amino acid sequences of A-domain by 10 amino acids from N-terminus, and we found that CAO accumulated excessively by deletion of specific amino acids sequences. From these results, we identified amino acid sequence which is essential for the regulatory mechanism.
