Anaerobic lipoxygenase activity from Chlorella pyrenoidosa.
The micro-alga Chlorella pyrenoidosa expresses an enzymatic activity that cleaves the 13-hydroperoxide derivatives of linoleic acid [13-hydroperoxy-9(Z),11(E)-octadecadienoic acid, 13-HPOD] and linolenic acid [13-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid, 13-HPOT] into volatile C(5) and non-volatile C(13) oxo-products. This enzymic activity initially was attributed to a hydroperoxide lyase enzyme; however, subsequent studies showed that this cleavage activity is the result of lipoxygenase activity under anaerobic conditions. Headspace analysis of the volatile products by GC/MS showed the formation of pentane when the substrate was 13-HPOD, whereas a more complex mixture of hydrocarbons was formed when 13-HPOT was the substrate. Analysis of the non-volatile cleavage products from 13-HPOD by liquid chromatography/MS indicated the formation of 13-oxo-9(Z),11(E)-tridecadienoic acid (13-OTA) along with the 13-keto-octadecadienoic acid derivative. When the substrate is 13-HPOT, liquid chromatography/MS analysis indicated the formation of 13-OTA as the major non-volatile product. Aldehyde dehydrogenase (AldDH) oxidizes 13-OTA to an omega-dicarboxylic acid, whereas alcohol dehydrogenase (ADH) reduces 13-OTA to an omega-hydroxy carboxylic acid. AldDH and ADH require the oxidized (NAD(+)) and reduced (NADH) forms of the cofactor NAD, respectively. By combining the action of AldDH and ADH into a continuous cofactor-recycling process, it is possible to simultaneously convert 13-OTA to the corresponding omega-dicarboxylic acid and omega-hydroxy carboxylic acid derivatives.
Nuñez
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United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA. anunez@arserrc.gov
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D000693:Anaerobiosis; D002708:Chlorella / Q000201:enzymology*; D019787:Linoleic Acid / Q000378:metabolism*; D008084:Lipoxygenase / Q000378:metabolism*; D008956:Models, Chemical; D013379:Substrate Specificity; D017962:alpha-Linolenic Acid / Q000378:metabolism*
D017962:alpha-Linolenic Acid; D019787:Linoleic Acid; D008084:Lipoxygenase