Isolation and characterization of a homogeneous isoenzyme of wheat germ acid phosphatase

An acid phosphatase (orthophosphoric monoester phosphohydrolase, acid optimum; EC 3.1.3.2) isoenzyme from wheat germ was purified 7000-fold to homogeneity. The effect of wheat germ sources and their relationship to the isoenzyme content and purification behavior of acid phosphatases was investigated. Extensive information about the purification and stabilization of the enzyme is provided. The instability of isoenzymes in the latter stages of purification appeared to be the result of surface inactivation together with a sensitivity to dilution that could be partially offset by addition of Triton X-100 during chromatographic procedures. Added sulfhydryl protecting reagents had no effect on activity or stability, which was greatest in the pH range 4-7. The purified isoenzyme was homogeneous by polyacrylamide gel electrophoresis and exhibited the highest specific activity and turnover number reported for any acid phosphatase. The molecular weights of the pure isoenzyme and of related isoenzymes from wheat germ were found to be identical (58,000). The pure isoenzyme contained a single polypeptide chain and had a negligible carbohydrate content. The amino acid composition was determined. Of the various reasons that were considered to explain isoenzyme occurrence, a genetic basis was considered most likely. The enzyme was found to exhibit substrate inhibition with some substrates below pH 6, while above pH 8 it exhibited downwardly curving Lineweaver-Burk plots of the type that are generally described as "substrate activation". The observation of a phosphotransferase activity was consistent with the formation of a covalent phosphoenzyme intermediate, while inactivation by diethyl pyrocarbonate was consistent with the presence of an active site histidine.

Acid phosphatase localization in the fungus Whetzelinia sclerotiorum

Acid phosphatase was localized by light and electron microscopy in chains of vacuoles in hyphal tip cells of Whetzelinia sclerotiorum. The enzyme was present in these vacuoles whether or not conditions favored extracellular acid phosphatase secretion. Apical vesicles, microbodies, Woronin bodies, and lipid bodies did not contain acid phosphatase. The implications regarding terminology of organelles in filamentous fungi are discussed with special reference to the fungal spherosome concept.

Effect of calcium, (2-chloroethyl) phosphonic acid and ethylene on bean leaf abscission

The effects of CaCl2, (2-chloroethyl) phosphonic acid (Ethephon) and ethylene on leaf abscission of debladed and intact bean plants (Phaseolus vulgaris L.) were studied. Ethephon (1000 μg/l) and ethylene (8 μl/l) induced abscission in debladed and intact plants in 24-72 h whereas IAA (10(-5)M), cycloheximide (10(-5)M) and CaCl2 (0.068M) delayed abscission in debladed plants. CaCl2 completely inhibited the abscission-enhancing effect of Ethephon in intact bean leaves. When CaCl2 and Ethephon were applied simultaneously to separate halves of the leaf blade, leaves with Ethephon applied closest to the pulvinus abscised rapidly; when CaCl2 was applied closest to the pulvinus, abscission was prevented. Calcium pre-treatment prior to ethylene (8 μl/l) treatment of debladed plants delayed abscission as compared to those treated with ethylene alone.

Isolation and properties of lysosomes from dark-grown potato shoots

A method is described for the isolation of lysosomal fractions from dark-grown potato shoots using a single stage separation on a Ficoll gradient. Peaks of acid hydrolase activity consisting of acid phosphatase, phosphodiesterase, ribonuclease, carboxylic esterase and β-glycerophosphatase were well separated from peaks of mitochondrial and glyoxysomal enzymes. A heavy lysosomal fraction with particle diameters from 0.1 to 1.6 μ and density of 1.10 g cm(-3) containing relatively low hydrolase activity was distinguishable from a light fraction with diameters 0.025 to 0.6 μ and density of 1.07 g cm(-3) with a higher level of hydrolase activity. Both fractions appeared heterogeneous by electron microscopy, but the fine structure of the membranes of both heavy and light lysosomes was similar. The heavy lysosomal fraction was rich in autophagic vacuoles (secondary lysosomes) containing organelles and amorphous cytoplasmic material. Both fractions were rich in ribonucleic acid.Freezing and thawing, high speed blending and ultrasonication either singly or in combination solubilised a maximum of ca. 30% of the acid phosphatase from crude lysosomal fractions derived from dark-grown potato shoots. Treatment with Triton X-100 and deoxycholate released appreciably more enzyme activity but acetone and carbon tetrachloride failed to solubilise any acid phosphatase. Only detergent treatments gave marked overrecovery of enzyme and indicated structure-linked latency. Liberation of enzyme from lysosomes varied with pH and was almost complete at both extremes of pH. Crude snake venom was rapid and effective in solubilising acid phosphatase from lysosomal preparations, purified phospholipase A was less effective and phospholipases C and D had negligible effects. Phospholipase and venom mediated release of acid phosphatase was accompanied by the coincident release of an acid end-product. Gel filtration of acid phosphatase liberated from heavy and light lysosomal fractions by snake venom digestion revealed that each of these fractions was characterised by the presence of distinct molecular forms of the enzyme. The nature of the association of acid phosphatase with potato shoot lysosomes is discussed.

Effect of senescence and hormone treatment on the activity of a β-1,3-glucan hydrolase in Nicotiana glutinosa leaves

A high level of activity of a β-1,3-glucan hydrolase is present in leaves of Nicotiana glutinosa and the enzyme is also present in the roots, midribs, petioles and stems. By comparison, very low levels of β-1,4-glucan hydrolase are found throughout the plant. The activity of the β-1,3-glucan hydrolase in leaves aged on the plant was found to increase 14-fold during the course of leaf senescence and to reach a maximum in yellow-green leaves. Detached leaves and leaf discs floated on water in the dark showed similar patterns of change.The increase in β-1,3-glucan hydrolase activity during senescence is apparently not due to the loss of an inhibitor from young green leaves or to the formation of an enzyme activator in yellow leaves. The enzyme in yellow leaves was electrophoretically indistinguishable from that in green leaves. The hydrolase is not firmly attached to the cell walls and is not present in the particulate fraction sedimenting at 105400xg for 60 min. Within the leaf cell it is therefore likely to be located either in the cytoplasm or in an easily disrupted structure such as a vacuole.The relationship of the hydrolase to leaf senescence was investigated by examining the effect of plant hormones on the changes in level of hydrolase, protein and chlorophyll in leaf discs during senescence. IAA (10 μM) and GA3 (50 μM) did not alter the normal patterns of change, whilst Kin (50 μM) delayed the loss of protein and chlorophyll and also delayed and decreased the rise in hydrolase activity. In contrast, ABA (190 μM) which increased the rate of loss of protein and chlorophyll, also caused a decrease in the rate and extent of the rise in hydrolase.Possible functions of the hydrolase in the leaf are discussed.

Fine-structural characterization of plant microbodies

Morphology and distribution of the relatively less well known organelles of plants have been studied with the electron microscope in tissues fixed in glutaraldehyde and postfixed in osmium tetroxide. An organelle comparable morphologically to the animal microbody and similar to the plant microbody isolated by MOLLENHAUER et al. (1966) has been encountered in a variety of plant species and tissues, and has been studied particularly in bean and radish roots, oat coleoptiles, and tobacco roots, stems and callus. The organelle has variable shape and is 0.5 to 1.5 μ in the greatest diameter. It has a single bounding membrane, a granular to fibrillar matrix of variable electron density, and an intimate association with one or two cisternae of rough endoplasmic reticulum (ER). Microbodies are easily the most common and generally distributed of the less well characterized organelles of plant cells. It seems very probable that they contain the enzymes characteristic of animal lysosomes (containing hydrolases) or animal microbodies (containing catalase and certain oxidases). Spherosomes are also possible sites of enzyme activity but are not as common or as widely distributed as microbodies. For this reason it appears likely that the particles designated as "plant lysosomes", "spherosomes", "peroxisomes", etc., in some of the cytochemical and biochemical studies on enzyme localization will prove to be microbodies.Variations in the morphology and ER associations of microbodies in tissues of bean and radish are described and discussed. "Crystal-containing bodies" (CCBs) are interpreted as a specialized type of microbody characteristic of metabolically less active cells. Stages in the formation of CCBs from microbodies of typical appearance are illustrated for Avena.The general occurrence of microbodies in meristematic and differentiating cells and their close association with the ER suggest that they may play active roles in cellular metabolism. The alterations in their morphology and numbers that are observed in certain differentiating cells suggest further that the enzyme complements and metabolic roles of microbodies might change during cellular differentiation. If so, microbodies could be the functional equivalent of both microbodies and lysosomes of animal cells.

Lysosomes of root tip cells in corn seedlings

Nine acid hydrolases are present in lysosomes which are found in the mitochondrial fraction of a cell-free extract prepared from root tips of corn seedlings.Light and heavy lysosomes can be distinguished. The latter are sedimentable in a sucrose-medium, the former only in sorbitol-medium. The fraction of heavy lysosomes is in turn composed of at least three populations of lysosomes differing in density and enzyme content.Light lysosomes are membrane-bound particles with diameters from 0.3 to 1.5 μ. Electron micrographs of frozen-etched tissue and isolated particles provide evidence that light lysosomes are identical with small vacuoles. This type of lysosome is characterized by presence of transaminases in addition to that of hydrolases. Heavy lysosomes are small spheres (diameters from 0.1-0.3 μ) with membranes resembling those of vacuoles and of the endoplasmic reticulum. These lysosomes are characterized by high specific activities of two oxydoreductases known to occur also in the membranes of the reticulum.The different types of particles are thought to represent stages of the development of the lysosomal apparatus; according to this hypothesis the large vacuole of parenchymatous cells represents the end product of this process.

A CYTOCHEMICAL STUDY OF ACID PHOSPHATASE AND NUCLEASE ACTIVITY IN THE PLASTID OF CLOSTERIUM ACEROSUM(1)

Acid phosphatase activity in Closterium acerosum has been studied using the Gomori and the azo dye procedures. A modification of the Gomori method was used for detecting the distribution of acid nucleases. The plastid is the major site of acid phosphatase activity luhich may be primarily within pyrenoids, between pyrenoids, or throughout the plastid. The Gomori procedure showed activity within the pyrenoids or in the central core of the plastid, whereas the azo dye method showed activity throughout with an occasional tendency to be localized near the ends. No other cytoplasmic activity was ob-served but evidence for occasional activity in the nucleus is presented. Alkaline phosphatase could not be detected. Acid nuclease activity, which results in the degradation of DNA, RNA, and RNA-Core, has been found in both the nucleus and the plastid. Plastid activity is heat labile, whereas nuclear activity is only slightly diminished after 5 min at 100 C. The results arc interpreted as indicating at least 2 acid phosphatases and 2 nucleases in C. acerosum. The findings are discussed with respect to the distribution of similar enzymes in other organisms.

[Intracellular localization and function of hydrolytic enzymes in tobacco]

1. Four acid hydrolases are partially sedimentable from cell free extracts of tobacco seedlings; these enzymes have the following pH-optima: acid protease pH 3,5; acid RNase pH 6,2; acid phosphatase pH 5,4 and 5,8 and acid unspecific esterase pH 5,5. 2. After differential centrifugation of cell free extracts the sedimentable hydrolases are recovered in the mitochondrial and microsomal fractions. 3. Treatments of the sedimentable material which destroy cytoplasmic membranes result in the solubilization of the acid hydrolases. 4. Isopycnic centrifugation in sucrose-gradients revealed the presence in cell free extracts of two particulate fractions carrying hydrolases; the relative densities of these particles are 1,11 and 1,09g cm(-3). 5. The lighter fraction consists mainly of spherosomes, as can be demonstrated by fluorescence microscopy of the particles stained with berberine sulfate. The heavier fraction probably consists of so-called prospherosomes. 6. The hydrolases from isolated spherosomes are able to digest isolated mitochondria in vitro. 7. The total activities as well as the quantity of sedimentable fractions are highest in seedlings and decrease markedly during ontogenesis of the plant. 8. The isolation of mature leaves causes the mobilization of the cytoplasm of the mesophyll cells within a few days; the chlorophyll disappears completely within 6 days whereas protein and lipid disappear gradually over a period of 16 days. 9. Immediately after the isolation of the leaves new sedimentable protease and esterase activity is formed; new RNase is synthesized a few days later. Soon after their formation these enzymes appear in the soluble fraction. 10. Treatment of detached leaves with kinetin delays the mobilization of chlorophyll, lipid and protein markedly. In addition the synthesis of acid hydrolases is suppressed almost completely. 11. The spherosomes are viewed as organelles of the plant cells equivalent to the lysosomes of animal cells. The intracellular localization and significance of the hydrolases occuring in the soluble fraction of cell free extracts is discussed. 12. The events taking place in mature detached leaves are interpreted as a catabolic mobilization of the cytoplasm due to the action of the spherosomal enzymes.

[Enzymatic characterization of lysosome equivalents (spherosomes) in corn seedlings]

1. The following acid hydrolases are partially sedimentable from cell-free extracts of corn seedlings: protease (pH-optimum 4,2), phosphatase (pH-optimum 5,0 and 6,5), unspecific esterase (pH-optimum 5,2), RNase (pH-optimum 6,5), arylsulphatase-C (pH-optimum 5,0) and α- and β-amylase (pH-optimum 7,0 and 5,0 respectively). 2. After differential centrifugation of cell-free extracts the sedimentable hydrolases are recovered mainly in the mitochondrial and microsomal fraction. 3. It could be demonstrated that the acid hydrolases protease, phosphatase, RNase, and esterase of the mitochondrial fraction are contained in membrane-bound particles. 4. Isopycnic centrifugation of cell-free extracts in sucrose gradients revealed the presence of three particulate fractions carrying hydrolases. The heaviest fraction has a relative density of 1,138 g\sdcm(-3) and contains acid protease,-phosphatase,-RNase, and acid esterase. A lighter fraction (d=1,105 g\sdcm(-3)) contains the same acid hydrolases. The specifically lightest cell fraction (d=1,070 g\sdcm(-3)) contains the acid hydrolases glucose-6-phosphatase, arylsulphatase-C and small amounts of \ga- and \gb-amylase activity. This fraction also contains NADH-diaphorase activity. 5. By means of enzymatic characterization and staining with fluorochromes the structures carrying hydrolases were identified as two kinds of spherosomes and as fragments of the endoplasmatic reticulum. From these results it is concluded that the spherosomes represent organelles equivalent to the lysosomes of animal cells. 6. β-Glucuronidase, phospholipase-C, lipase, and arylsulphatase A and-B, all of with are typical enzymes of animal lysosomes, are completely absent in cell-free extracts of corn seedlings. 7. The isolated spherosomes do not exhibit indophenoloxydase activity; thus the histochemical demonstration of this enzyme in spherosomes must be considered to be an artifact. 8. Isolated lipid droplets, spherosomes, prospherosomes, and mitochondria incorporate H(-3)-acetate into lipids. Consequently they contain all the nessesary enzymes for lipid synthesis. The high activity of lipid synthesis in the spheroromes points to a possible conversion of these organelles into lipid bodies. 9. Two transaminases are partially bound to the mitochondria; the rest of the activity is probably bound to fragments of membranes less dense than an 18% sucrose solution.