Midchain hydroxylation

Cutin is composed chiefly of a C16 and/or a Cis family of monomers (Fig. 4.2). The usual components of the former are palmitic acid, 16-hydroxypalmitic acid, and 10,16-dihy-droxypalmitic and/or its positional isomers in which the midchain hydroxyl group is at C9, Cs, or C7. Monomers that could be derived from the above acids by further oxidation or reduction also have been found in cutin from some plants. The C18 family consists of stearic acid, oleic acid, linoleic acid, 18-hydroxyoleic acid, 18-hydroxy-9,10-epoxystearic acid, and 9,10,18-trihydroxystearic acid together with their A-12 unsaturated analogs. Members of the Cie family are the dominant components of the cutin of fast-growing plants, whereas the cutin of slower-growing plants with a thicker cuticle consists of a mixture of C16 and C18 monomers (Harwood, 1980). 

Cutin is composed of chiefly a Cig family and/or a Cig family of monomers (Fig. 9). The usual meyor components of the former are palmitic acid, 16-hy-droxypalmitic acid, and 10,16-dihydroxypalmitic acid and/or its positional isomers, in which the midchain hydroxyl group is at C-9, C-8, or C-7 (Kolat-tukudy, 1977b Brieskom, 1978). The dihydroxy acid from papaya and tomato cutin showed a plain-positive rotation, and therefore the L configuration has been assigned to this major cutin monomer (Espelie and... 

Soliday C L, Kolattukudy P E 1978 Midchain hydroxylation of 16-hydroxypalmitic acid by the endoplasmic reticulum fraction from germinating Vida faba. Arch Biochem Biophys 188 338-347... 

Castor oil is a unique natural product used in many industries and many types of products. With its 85-90% content of the hydroxy FA ricinoleic acid, castor oil provides this FA at the equivalent of a technical grade of purity, a rare natural phenomenon. The uses of castor oil in industry are limited by the availability of the oil. The presence of a midchain hydroxyl group and the polyol nature of castor oil provide nearly endless possibilities for chemists to develop new applications for the oil. More widespread cultivation of the castor plant will expand utilization of castor oil by industry. 

Finally, since fatty acid hydroxylations at the o), 00-1, 00-2, 00-3, and co-4 positions also occur in plants and bacteria °, acetylenic fatty acids have also been employed to examine whether these hydroxylases are mechanistically similar to their mammalian counterparts and/or to identify the role of specific plant and bacterial P450 enzymes °. Thus, midchain and terminal acetylenes such as 10-dodecynoic acid have been used as probes of plant lauric acid oo-hydroxylases . Similarly, 17-ODYA has been shown to inactivate P450g, 3 (CYP108), an enzyme that hydroxylates fatty acids at positions other than the terminal (oo) carbon, through a heme alkylation mechanism . 

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