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Lipoxygenase from potato tubers. Partial purification and properties of an enzyme that specifically oxygenates the 9-position of linoleic acid.

ABSTRACT: A lipoxygenase (EC 1.13.1.13) was partially purified from potato tubers and was shown to differ from previously characterized soya-bean lipoxygenases in the positional specificity and pH characteristics of the oxygenation reaction. The potato enzyme converted linoleic acid almost exclusively (95%) into 9-d-hydroperoxyoctadeca-trans-10,cis-12-dienoic acid. The 13-hydroperoxy isomer was only a minor product (5%). Linolenic acid was an equally effective substrate, which was also oxygenated specifically at the 9-position. The enzyme had a pH optimum at 5.5-6.0 and was inactive at pH9.0. A half-maximal velocity was obtained at a linoleic acid concentration of 0.1mm. No inhibition was observed with EDTA (1mm) and cyanide (1mm) or with p-chloromercuribenzoate (0.2mm). Haemoproteins were not involved in the lipoxygenase activity. The molecular weight of the enzyme was estimated from gel filtration to be approx. 10(5). Preliminary evidence suggested that the enzyme oxygenated the n-10 position of fatty acids containing a penta(n-3, n-6)diene structure.

SUBMITTER: Galliard T

PROVIDER: S-EPMC1177158 | biostudies-other | 1971 Sep

REPOSITORIES: biostudies-other

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Project description:This is a study to characterize gene expression profiles in stored Russet Burbank potato tubers. Tubers were harvested from commercial fields in the central sands region of Wisconsin in the fall of 2006. The tubers were put into storage at 55 degrees F for preconditioning and wound healing. Shortly after the temperature of the storage bin began to decrease, uniform, healthy tubers were selected for use in this microarray analysis. Tubers were at 53.6 degrees F at this time, and pieces of starch-storing tissue were collected for use as the reference sample. Other tubers were moved to temperature-controlled lockers and these were cooled gradually to either 48 or 40 degrees F following industry standard procedures. The expectation was that tubers held at 48 degrees would not have a significant accumulation of glucose and fructose, but that tubers cooled to 40 degrees would undergo low temperature sweetening and accumulate glucose and fructose to a degree that is unsuitable for processing. Three weeks later, when the locker temperatures were 48 degrees F and 41.5 degrees F, tissue samples were collected for RNA analysis. After another three weeks, samples were collected from tubers at 48 degrees F and 40 degrees F. At that time some tubers were moved from the 48 degree locker to the 40 degree locker in order to see if gene expression changes observed as a result of gradual cooling are similar to those that occur following a sudden decrease in temperature. Three weeks later, samples were collected from tubers held at 48 degrees F, tubers held at 40 degrees F, and from the tubers that were moved from 48 to 40 degrees F. At this time another set of tubers was transferred from 48 degrees to 40 degrees. Three weeks later the last samples were harvested from tubers held at 48 degrees F, from tubers held at 48 degrees F and from tubers that were transferred three weeks prior from 48 to 40 degrees. RNA was isolated from tissue extracted from three tubers. Keywords: Reference design

Project description:Background and aimsThe three-dimensional distributions of mineral elements in potato tubers provide insight into their mechanisms of transport and deposition. Many of these minerals are essential to a healthy human diet, and characterizing their distribution within the potato tuber will guide the effective utilization of this staple foodstuff.MethodsThe variation in mineral composition within the tuber was determined in three dimensions, after determining the orientation of the harvested tuber in the soil. The freeze-dried tuber samples were analysed for minerals using inductively coupled plasma-mass spectrometry (ICP-MS). Minerals measured included those of nutritional significance to the plant and to human consumers, such as iron, zinc, copper, calcium, magnesium, manganese, phosphorus, potassium and sulphur.Key resultsThe concentrations of most minerals were higher in the skin than in the flesh of tubers. The potato skin contained about 17 % of total tuber zinc, 34 % of calcium and 55 % of iron. On a fresh weight basis, most minerals were higher in tuber flesh at the stem end than the bud end of the tuber. Potassium, however, displayed a gradient in the opposite direction. The concentrations of phosphorus, copper and calcium decreased from the periphery towards the centre of the tuber.ConclusionsThe distribution of minerals varies greatly within the potato tuber. Low concentrations of some minerals relative to those in leaves may be due to their low mobility in phloem, whereas high concentrations in the skin may reflect direct uptake from the soil across the periderm. In tuber flesh, different minerals show distinct patterns of distribution in the tuber, several being consistent with phloem unloading in the tuber and limited onward movement. These findings have implications both for understanding directed transport of minerals in plants to stem-derived storage organs and for the dietary implications of different food preparation methods for potato tubers.

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Lipoxygenase from potato tubers. Partial purification and properties of an enzyme that specifically oxygenates the 9-position of linoleic acid.

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