Zr. Sun et al., CLONING AND FUNCTIONAL-ANALYSIS OF THE BETA-CAROTENE HYDROXYLASE OF ARABIDOPSIS-THALIANA, The Journal of biological chemistry, 271(40), 1996, pp. 24349-24352
An Arabidopsis thaliana cDNA encoding the enzyme beta-carotene hydroxy
lase was identified by functional complementation in Escherichia coli.
The product of this cDNA adds hydroxyl groups to both beta rings of t
he symmetrical beta-carotene (beta,beta-carotene) to form zeaxanthin (
beta,beta-carotene-3,3'-diol) and converts the monocyclic beta-zeacaro
tene (7',8'-dihydro-beta,psi-carotene) to hydroxy-beta-zeacarotene (7'
,8'-dihydro-beta,psi-carotene-3-ol). The epsilon rings of delta-carote
ne (epsilon,psi-carotene) and alpha-zeacarotene (7',8'-dihydro-epsilon
,psi-carotene) are poor substrates for the enzyme, The predicted amino
acid sequence of the A. thaliana enzyme resembles the four known bact
erial beta-carotene hydroxylase enzymes (31-37% identity) but is much
longer, with an N-terminal extension of more than 130 amino acids. Tru
ncation of the cDNA to produce a polypeptide lacking the first 69 amin
o acids does not impair enzyme activity in E. coli. Truncation to yiel
d a polypeptide of a length comparable with the bacterial enzymes (lac
king 129 N-terminal amino acids) resulted in the accumulation of the m
onohydroxy intermediate beta-cryptoxanthin (beta,beta-carotene-3-ol),
predominantly, when beta-carotene was provided as the substrate. It is
suggested that amino acid residues 70-129 of the A. thaliana enzyme m
ay play a role in formation of a functional homodimer.