Enzyme activities of the β-oxidation pathway in spinach leaf peroxisomes

The Craft of Peroxisome Purification-A Technical Survey Through the Decades

Purification technologies are one of the working horses in organelle proteomics studies as they guarantee the separation of organelle-specific proteins from the background contamination by other subcellular compartments. The development of methods for the separation of organelles was a major prerequisite for the initial detection and characterization of peroxisome as a discrete entity of the cell. Since then, isolated peroxisomes fractions have been used in numerous studies in order to characterize organelle-specific enzyme functions, to allocate the peroxisome-specific proteome or to unravel the organellar membrane composition. This review will give an overview of the fractionation methods used for the isolation of peroxisomes from animals, plants and fungi. In addition to "classic" centrifugation-based isolation methods, relying on the different densities of individual organelles, the review will also summarize work on alternative technologies like free-flow-electrophoresis or flow field fractionation which are based on distinct physicochemical parameters. A final chapter will further describe how different separation methods and quantitative mass spectrometry have been used in proteomics studies to assign the proteome of PO.

Malate dehydrogenase isoenzymes: cellular locations and role in the flow of metabolites between the cytoplasm and cell organelles

Malate dehydrogenases belong to the most active enzymes in glyoxysomes, mitochondria, peroxisomes, chloroplasts and the cytosol. In this review, the properties and the role of the isoenzymes in different compartments of the cell are compared, with emphasis on molecular biological aspects. Structure and function of malate dehydrogenase isoenzymes from plants, mammalian cells and ascomycetes (yeast, Neurospora) are considered. Significant information on evolutionary aspects and characterisation of functional domains of the enzymes emanates from bacterial malate and lactate dehydrogenases modified by protein engineering. The review endeavours to give up-to-date information on the biogenesis and intracellular targeting of malate dehydrogenase isoenzymes as well as enzymes cooperating with them in the flow of metabolites of a given pathway and organelle.

Apparent induction of key enzymes of the glyoxylic acid cycle in senescent barley leaves

The activities of two key enzymes of the glyoxylic-acid cycle, isocitrate lyase and malate synthase, can barely be detected in mature, presenescent primary leaves of barley (Hordeum vulgare L.) but are apparently induced in senescent leaf tissue. Upon incubation of leaf segments in permanent darkness, the activities appear and increase dramatically up to the sixth day and thereafter decline. The glyoxylic-acid cycle may thus be functional during foliar senescence. The main period of galactolipid loss is characterized by RQ values as low as 0.63, indicating that long-chain fatty acids produced from thylakoidal acyl-lipids may be utilized for gluconeogenesis involving corresponding glyoxisomal metabolic pathways. Foliar senescence may be characterized by a peroxisomeglyoxysome transition analogous to the glyoxisome-peroxisome transition in greening cotyledons of fat-storing seeds.

Is protein degradation correlated with either the charge or size of Lemna proteins?

Evidence is presented that the organelles of Lemna minor do not degrade as functional units. The proteins of Lemna show wide differences in their rates of degradation and ribulose bisphosphate carboxylase (EC 4.1.1.39) has a particularly slow rate of degradation. Contrary to some earlier evidence, we found no correlation between the rate of soluble-protein degradation and either charge or size of proteins. We could find no correlation between protein degradation and subunit size in any of the organelles of Lemna.

The dual location of β-oxidation enzymes in germinating pea cotyledons

β-Oxidation enzymes were detected both in the mitochondria and microbodies of pea cotyledons. Intact mitochondria did not show β-oxidation enzyme activity but in ruptured mitochondria this activity was high. It is apparent that the mitochondrial membrane barrier prevents rapid access of acyl-CoA substrates to matrix β-oxidation sites. Removal of the membrane barrier permits rapid access of acyl-CoAs and these enzyme activities may then be measured.

Localization of β-oxidation enzymes in peroxisomes isolated from nonfatty plant tissues

Peroxisomes from spinach leaves, mungbean hypocotyls, and potato tubers catalyze a palmitoyl-CoA-dependent, KCN-insensitive O2 uptake. In the course of this reaction O2 is reduced to H2O2 in a 1:1 stoichiometry and palmitoyl-CoA oxidized, in a 1:1 stoichiometry, to a product serving as substrate for enoyl-CoA hydratase. These findings demonstrate the existence of a peroxisomal acyl-CoA oxidase in these tissues. Enoyl-CoA hydratase (EC 4.2.1.17), 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35), and thiolase (EC 2.3.1.9) are also associated with the peroxisomes from mung-bean hypocotyls and potato tubers (as well as with spinach leaf peroxisomes as recently reported; Gerhardt 1981, FEBS Lett. 126, 71). The low activities of these enzymes in mitochondrial fractions seem to be due to contaminating peroxisomes since the ratio of β-oxidation enzyme activities to catalase activity did not significantly differ between peroxisomal and mitochondrial fractions isolated on sucrose density gradients. The proof of localization of β-oxidation enzymes in peroxisomes without glyoxysomal function leads to the concept that fatty-acid oxidation is a consistent basic function of the peroxisome in cells of higher plants.

Fatty acid β-oxidation and glyoxylate cycle enzyme activities of induced glyoxysomes from anise suspension cultures

Homogenates of dedifferentiated anise (Pimpinella anisum L.) suspension cultures grown in B-5 medium with sucrose as source of carbon show all but 3 glyoxysomal enzyme activities: NAD-dependent oxidation of palmitoyl-CoA, isocitrate lyase, and malate synthase are lacking. Substitution of 20 mmol/l acetate for sucrose leads to the appearance of these enzyme activities. Only then glyoxysomes with a buoyant density of 1.23 kg/l in sucrose gradients are formed showing the enzyme activities for both ß-oxidation of fatty acids and glyoxylate cycle. Quantitatively and qualitatively they resemble glyoxysomes isolated from endosperm of 4 d old anise seedlings. Therefore, the suspension cultures constitute a valuable system for the study of both mechanisms and regulation of glyoxysome formation in anise.