Formation of Carotenoid Oxygenated Cleavage Products - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 216

504.4

COOH

CHO

O 502

HO

CH 2 OH

HOH 2 C

547.2

O O

562

O

O

FIGURE 11.1 Chemical structures of carotenoid oxidation products occurring in nature: apocarotenoids:10′-
apolycopen-10′-oic acid (504.4), apo-10′-violaxanthal (502), diapocarotenoid:rosal uin (547.2), and seco-
carotenoid:β-carotenone (562). The compound number corresponds to those in Britton et al. (2004).

After a short presentation of naturally occurring oxygenated cleavage compounds, we describe
different ways by which they can be formed starting from the parent carotenoid, and we give some
information on their mechanisms of formation when available in the literature.

11. 2 OCCURRENCE IN NATURE AND FORMATION
IN BIOCHEMICAL SYSTEMS
In nature, some 117 apocarotenoids have been reported, 88 of which have been fully identii ed.
Another six naturally occurring seco-carotenoids have been referenced as carotenoids (Britton
et al. 2004). Apo- and seco-carotenoids represent around 15% of the carotenoids so far reported.
This subfamily of carotenoids would be even larger if one considers retinoids and norisoprenoids,
but these compounds are excluded by nomenclature rules (IUPAC 1971, 1975) that dictate that they
are not deemed to be carotenoids because of the absence of the two central methyl groups (at C20
and C20 ). Retinoic acid, retinal, and retinol (vitamin A) can be considered as carotenoid oxygen-

ated cleavage products of the provitamin A carotenoids, such as

′

-cryptoxanthin, and
are formed in humans by enzymatic cleavage. The theories of their mechanism of formation were
for many years controversial, with two hypotheses based on a central and/or excentric cleavage.
Krinsky and coworkers have shown that the excentric cleavage of

β -carotene or β

β -carotene occurs, giving rise to

a series of apocarotenals and even retinoic acid, when -carotene is incubated in various biochemi-

cal systems (Tang et al. 1991, Wang et al. 1991, 1992, Yeum et al. 1995). It is only recently that
cleavage enzymes have been identii ed. The i rst central cleavage enzyme was partially purii ed via
cloning of its encoding cDNAs from different organisms (von Lintig and Vogt 2000, Wyss et al.
2000, Paik et al. 2001, Redmond et al. 2001) and was shown to be a monooxygenase-type enzyme
(Leuenberger et al. 2001). Another enzyme that catalyzes the excentric cleavage of

β

β -carotene in

the 9 -carotenal (Kiefer

et al. 2001). A similar enzyme from ferret, a model used to study carotenoid metabolism in humans,

′ ,10 ′ position was shown to occur in humans and mice producing apo-10 ′