The synthesis of several substrate analogues of the enzyme beta,beta -carot
ene 15,15'-monooxygenase is reported. The substrate specificity of enriched
enzyme fractions isolated from chicken intestinal mucosa was investigated.
Regarding substrate binding/cleavage, these experiments demonstrate that i
) any deviation from the 'rod-like' beta,beta -carotene structure is not to
lerated, ii) one 'natural', unsubstituted beta -ionone ring is required, ii
i) the position and presence of the Me groups attached to the polyene chain
is significant. These results suggest a hydrophobic barrel-like substrate
binding site in which the protein's amino acid residues through interaction
with the Me groups, direct the central C=C bond in binding distance to the
active site's metal-oxo center, supporting the unique regiospecificity of
cleavage to retinal (provitamin A).