In animals, fatty acid desaturases catalyze key reactions in the synthesis of arachidonic acid and other polyunsaturated fatty acids. A search of the Caenorhabditis elegans DNA databases, using the sequences of Arabidopsis genes, identified several putative desaturases. Here we describe the characterization of the first of these genes, fat-1. The predicted protein encoded by a fat-1 cDNA showed 32-35% identity with both FAD2 and FAD3 of Arabidopsis. When expressed in transgenic plants, fat-1 resulted in a 90% increase in the proportion of ␣-linolenic acid in root lipids. Wild-type Arabidopsis incorporated -6 fatty acids (⌬8,11,14-20:3 and ⌬5,8,11,14-20:4) into membrane lipids but did not desaturate them. By contrast, fat-1 transgenic plants efficiently desaturated both of these fatty acids to the corresponding -3 products. These findings indicate that the C. elegans fat-1 gene encodes the first animal representative of a class of glycerolipid desaturases that have previously been characterized in plants and cyanobacteria. The FAT-1 protein is an -3 fatty acyl desaturase that recognizes a range of 18-and 20-carbon -6 substrates.
Activated oxygen or oxygen free radical mediated damage to plants has been established or implicated in many plant stress situations. The extent of activated oxygen damage to potato (Solanum tuberosum L.) tubers during low temperature storage and long-term storage is not known. Quantitation of oxygen free radical mediated damage in plant tissues is difficult. However, it is comparatively easy to quantitate endogenous antioxidants, which detoxify potentially damaging forms of activated oxygen.Three tuber antioxidants, superoxide dismutase, catalase, and atocopherol were assayed from four potato cultivars stored at 3°C and 90C for 40 weeks. Tubers stored at 30C demonstrated increased superoxide dismutase activities (up to 72%) compared to tubers stored at 90C. Time dependent increases in the levels of superoxide dismutase, catalase, and a-tocopherol occurred during the course of the 40 week storage. The possible relationship between these increases in antioxidants and the rate of activated oxygen production in the tubers is discussed.
~l h e enzyme UDP-glucose pyrophosphorylase (UCPase) from potato (Solanum tuberosum L. cv Norchip) tubers was purified 177-fold to near homogeneity and to a specific activity of 1099 international unitslmg of protein. l h e molecular mass of the purified enzyme was 53 k D as determined by SDS-PACE and gel filtration. lmmunological and activity assays detected UGPase at similar levels in potato stems, stolons, and tubers. Leaves and roots contained lower levels of UCPase activity and protein. LineweaverBurk plots for substrates inorganic pyrophosphate and UDP-glucose were linear in the pyrophosphorolytic diredion, yielding K,,, values of 0.13 and 0.14 mM, respectively. However, LineweaverBurk plots for the substrates glucose-1-P and UTP were biphasic in nature when UCPase was assayed in the direction of UDP-glucose synthesis. At physiological substrate concentrations (Le. from 0.05-0.20 mM), K,,, values of 0.08 mM (glucose-1-P) and 0.12 mM (UTP) were obtained. When substrate concentrations increased above 0.20 mM, K,,, values increased to 0.68 mM (glucose-1-P) and 0.53
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