Philippe Matile

The vacuole as the lysosome of the yeast cell

SummaryVacuoles can be isolated by flotation from suspensions of lysed proto-plasts in the presence of Ficoll. The purity of the respective preparations is demonstrated by the complete absence of enzymes of the mitochondria and of the groundplasm, as well as by morphological observations. Hydrolytic enzymes (two acid proteases, p-nitrophenylacetate-esterase, RNase and leucylaminopeptidase) are present in high specific activities in isolated vacuoles. The vacuole therefore represents the lysosome of the yeast cell.

Lysosomes of root tip cells in corn seedlings.

SummaryNine 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.

Vacuolar dynamics in synchronously budding yeast

SummaryA simple and rapid method for obtaining synchronously budding cultures of Saccharomyces cerevisiae is described. Synchronous cultures were started with homogeneous cell fractions isolated from exponentially growing cultures by isopycnic centrifugation in osmotically inactive media. The technique of fractionation is based on changes of cell density throughout the budding cycle. These changes are correlated with vacuolar changes observed in the light and electron microscope. During bud initiation the large vacuoles in late budding cells shrink and fragment into small vacuoles. Simultaneously the density of the cells increases. Later stages of the budding cycle are characterized by the distribution of the small vacuoles between mother and daughter cell, followed by their fusion and expansion, and by a decreasing density of the cells. The relative changes in cell density and dry weight and in the content of different macromolecules during the budding cycle suggest a cyclic change between utilization of endogenous and exogenous substrates. This is discussed in terms of a cyclic consumption and accumulation of vacuolar pools.

Isolation of glucanase-containing vesicles from budding yeast

SummaryIn an investigation of the role of glucanases in modifying yeast cell walls at the location of new buds, vesicles derived from the endoplasmic reticulum, which are secreted locally into the cell wall of growing buds, and may be involved in the secretion of glucanases, have been isolated.In yeast, exo-β-1,3-glucanase is present both extra- and intracellularly. Exponentially growing cells contain at least 11% of the enzyme activity intracellularly (within the plasmalemma). Most of this intracellular glucanase is sedimentable. Of the three classes of subcellular particles that contain glucanase, one is almost completely absent from stationary phase cells and largely absent from cells of the late budding phase of the cell cycle. These particles were isolated from budding cells by combined differential and density gradient centrifugation. They contain exo- and endo-β-1,3-glucanases, mannan and protein. The isolate consists mainly of membrane-bounded vesicles with diameters corresponding to those of the secretory vesicles observed in situ. It is concluded that these particles are identical with the vesicles derived from the endoplasmic reticulum.

Zur Charakterisierung der Gasvacuolen der Blaualge Oscillatoria rubescens

ZusammenfassungDie Hohlspindeln aus Oscillatoria rubescens enthalten in ihrem Innern ein Gas und sind die Elemente der lichtmikroskopisch beobachtbaren Gas- oder Pseudovacuolen. Sie können mit Hilfe der Dichtegradienten-zentrifugation von den Thylakoiden, die den photosynthetischen Apparat enthalten, und den anderen Strukturen abgetrennt werden. Zwar verlieren sie bei der Isolation ihre Spindelform, doch besitzen die entstandenen Blasen eine mit Osmium stabilisierbare Membran, an deren Aufbau die zwei Polyene β-Carotin und 4-Keto-β-Carotin und vermutlich Fettsäuren beteiligt sind.

Subcellular distribution of yeast invertase isoenzymes

Homogenates from yeast cells contain 1% or less of sedimentable invertase activity. Sedimentability is equally low in homogenates from cells repressed or derepressed with regard to invertase secretion. Intracellularly, the mannanprotein form of invertase is largely localized in vacuoles whereas the small isoenzyme is largely present in the soluble cell fraction. These findings indicate that vesicles are not involved in the secretion of invertase. A soluble mode of invertase secretion is discussed.

Catabolism of carotenoids: Involvement of peroxidase?

In primary leaves of barley allowed to senesce under natural conditions, carotenoids, like chlorophylls, disappear gradually. Commercial horse-radish peroxidase catalizes the oxidation of lutein to unknown colorless products. This reaction depends on the presence of 2,4 dichlorophenol. It is independent of peroxide but is nullified in the presence of catalase. Preparations of thylakoids from barley chloroplasts show an activity with features comparable to those of horse-radish peroxidase.

On the Fading of an Ephemeral Flower

Summary The mechanism in the ribs which leads to the curling up of the corolla of Ipomoea tricolor was investigated. It seems that two processes are involved in this movement. Due to differential turgor changes the ribs start to roll up. At the same time extracellular enzymes cause a reduction of the tensions in the structure of the cell walls. This modification enables the ribs to continue the curling up process.

Introduction: Lysis and the Lytic Compartment

The metabolism of natural ecosystems is characterized by a balance between the primary production in the photoautotrophs and the utilization and eventual mineralization of primary products along the complex food chains. Obviously, the lytic phenomena such as degradation of macromolecular compounds produced in plants by herbivorous animals and in saprophytic microorganisms play a prominent role. It is often less appreciated that the plants themselves produce lytic enzymes that are capable of degrading their own cellular constituents. Hence, lysis must have a significant function in the plant’s own metabolism.

Functions of the Lytic Compartment

Although it has been recognized that various cellular constituents are metabolically labile, detailed studies on turnover have mainly concerned protein and, to a lesser extent, RNA. This is, of course, due to the importance of protein turnover in biochemical cell differentiation. When a species of protein is synthesized at the expense of amino acids produced by the hydrolysis of other protein species, cells may consequently change their biochemical nature. There are, however, comparatively few examples which demonstrate this particular aspect of protein turnover.