Diverse Activities of Carotenoid Cleavage Oxygenases - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 410

At CCD7 (Schwartz et al. 2004). Organic solvent addition (dioxane, DMSO, methanol or acetone)
improved activity under low concentrations (Mathieu et al. 2007). Short chain aliphatic alcohols
activated the enzymes although the reason for this activation is unclear (probably due to inl u-
ences on substrate accessibility or micellar structure). An increase in activity was observed for all
aliphatic alcohols tested, although the optimal concentration lessened with increasing log P values
(Schilling et al. 2007).
19.7 CONCLUSIONS AND OUTLOOK
To date, the majority of the literature on CCO enzymes has been devoted to descriptions of the
homologs from different organisms. However, despite the large number of CCOs described so far,
relatively little is known about the mechanism of this novel class of oxygenases. The low in vitro
activities obtained with recombinant enzymes is a major impediment to biochemical studies. The
necessity of carotenoid cleaving enzymes to interact with membranes to access their hydrophobic
carotenoid substrates creates difi culties in creating optimal assay conditions. With only one solved
structure of a microbial apocarotenoid cleaving CCO, structural analysis of this class of enzymes
severely lags behind other oxygenase family members.
Despite these difi culties, research on CCO enzymes represents one of the most exciting i elds of
carotenoid research. As more examples are discovered in different organisms, the evolutionary his-
tory and current biological functions appear even more complex. The three major areas of research
being pursued that will provide the most exciting results include (1) elucidation of the signaling
pathways through identii cation of downstream targets for the cleavage products and identii cation
of the signals themselves (in the case of CCD7 and CCD8), (2) characterization of the enzymes'
catalytic mechanism and mechanisms of substrate and cleavage site selection, and (3) a greater
understanding of evolution of the nonheme iron oxygenases family in nature.
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