ATP-dependent acidification of intact and disrupted lysosomes. Evidence for an ATP-driven proton pump

The chromaffin vesicle and the energetics of storage organelles

In the chromaffin vesicle, energy for amine transport is provided by a proton-translocating adenosine triphosphatase. The ATPase pumps protons into the vesicle; a pair of protons is then exchanged for each catecholamine taken up. In terms of transport, the adrenal chromaffin vesicle is an important model for non-mitochondrial organelles of all types. These organelles include adrenergic synaptic vesicles, other secretory and neurotransmitter storage vesicles, and lysosomes and other intracellular organelles as well. The membranes of these organelles all possess an ATPase that pumps H+ ions into the vesicles. This proton pump presumably drives the transport of ions and molecules into the organelle and powers other energy-requiring functions of the membrane.

Effects of hyperthermia on plasma glycoprotein catabolism by the isolated perfused rat liver

Clearance and degradation of the glycoprotein, asialofetuin (AF), by the isolated perfused rat liver at supranormal temperatures were investigated. The half-life for disappearance of AF was similar at 37, 41, and 42 degrees C, P greater than 0.05. There was a significant difference between the amount of hydrolysis of AF at 37, 41, and 42 degrees C, P less than 0.05. This indicates that there was significant retardation of lysosomal proteolysis or receptor endocytosis by the hepatocyte at elevated temperatures.

Sorting and recycling of cell surface receptors and endocytosed ligands: the asialoglycoprotein and transferrin receptors

With few exceptions, receptor-mediated endocytosis of specific ligands is mediated through clustering of receptor-ligand complexes in coated pits on the cell surface, followed by internalization of the complex into endocytic vesicles. During this process, ligand-receptor dissociation occurs, most probably in a low pH prelysosomal compartment. In most cases the ligand is ultimately directed to the lysosomes, wherein it is degraded, while the receptor recycles to the cell surface. We have studied the kinetics of internalization and recycling of both the asialoglycoprotein receptor and the transferrin receptor in a human hepatoma cell line. By employing both biochemical and morphological/immunocytochemical approaches, we have gained some insight into the complex mechanisms which govern receptor recycling as well as ligand sorting and targeting. We can, in particular, explain why transferrin is exocytosed intact from the cells, while asialoglycoproteins are degraded in lysosomes. We have also localized the intracellular site at which endocytosed receptor and ligand dissociate.

Intracellular membrane traffic: pathways, carriers, and sorting devices

Multiple pathways of intracellular membrane traffic have been detected in various cell types. The major established routes are (a) the exocytosis pathway, utilized in secretory cells for the discharge of secretory products, and which is also believed to be used for delivery of intrinsic membrane glycoproteins in all cell types; (b) the plasmalemma to Golgi route, also highly developed in secretory cells, which is believed to be utilized for the recovery and recycling of the membranes of containers used in packaging of secretory products (i.e., secretory granules or vesicles); (c) the lysosomal pathway, which is available in all cells but is the major route utilized in phagocytic cells; (d) the transcellular route, which represents the major type of traffic encountered in nonfenestrated, capillary endothelial cells and also appears to be the preferred route for the transport of immunoglobulins (intact) across cells; and (e) the biosynthetic pathways used for transport of secretory products, lysosomal enzymes, and membrane proteins from the ER to the Golgi complex and for transport of lysosomal enzymes from the Golgi complex to lysosomes in all cell types. It has become clear that cells repeatedly reutilize or recycle the vesicular membranes involved in carrying out these various transport operations. Clathrin-coated vesicles have been found to be involved in transport along all the routes detected so far, suggesting that there are multiple populations of coated vesicles with different transport functions in every cell. It has become clear that considerable sorting of membrane constituents and ligands takes place at the plasmalemma (receptor-mediated uptake), in the Golgi complex, and in endosomes. The Golgi complex is the intracellular site where much of the biosynthetic and recycling membrane traffic converges and where products are sorted and directed to their correct destinations. In summary, we have become aware of the existence of multiple pathways of membrane traffic and of the extensive reutilization or recycling of membranes that occurs in cells. The basic pathways are similar in all cells except that some are emphasized or deemphasized according to the predominant function and organization of a given cell type. What now remains to be done is to determine how these transporting membranes and the membranes of the receiving compartments are constructed, how their specific interactions are controlled, and how individual cell types utilize these pathways to carry out their specific functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and properties of an ATPase in vacuolar membranes of Neurospora crassa

Using a vacuolar preparation virtually free of contamination by other organelles, we isolated vacuolar membranes and demonstrated that they contain an ATPase. Sucrose density gradient profiles of vacuolar membranes show a single peak of ATPase activity at a density of 1.11 g/cm3. Comparison of this enzyme with the two well-studied proton-pumping ATPases of Neurospora plasma membranes and mitochondria shows that it is clearly distinct. The vacuolar membrane ATPase is insensitive to the inhibitors oligomycin, azide, and vanadate, but sensitive to N,N'-dicyclohexylcarbodiimide (Ki = 2 microM). It has a pH optimum of 7.5, requires a divalent cation (Mg2+ or Mn2+) for activity, and is remarkably unaffected (+/- 20%) by a number of monovalent cations, anions, and buffers. In its substrate affinity (Km for ATP = 0.2 mM), substrate preference (ATP greater than GTP, ITP greater than UTP greater than CTP), and loss of activity with repeated 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid washes, the vacuolar membrane ATPase resembles the F1F0 type of ATPase found in mitochondria and differs from the integral membrane type of ATPase in plasma membranes.

Effects of ATP on lysosomes: inhibition of the loss of latency caused by cooling

Triton-filled lysosomes from rat liver and a crude lysosomal fraction from livers of rats not injected with Triton have been used to study the ability of ATP to protect lysosomes against the effects of incubation in vitro at 37 degrees C. When incubation was carried out in a sucrose-NH4Cl medium at pH 8.0 or in buffer containing 0.15 M KCl at pH 7.4, ATP protected against the loss of lysosomal enzyme latency that occurred at 37 degrees C and also against the additional loss of latency that occurred when the incubated lysosomes were cooled to 0 degrees C. The inhibition of the effects of cooling was found to result from a decrease in the loss of latency caused specifically by cooling the lysosomes through the temperature range of the membrane phase transition (15-0 degrees C); ATP did not affect the basic rate of loss of latency at 0 degrees C. Protection was minimal when incubation was carried out in 1 mM ethylenediaminetetraacetic acid without added divalent metal ion and was enhanced by the addition of either Mg2+ or Ca2+. Kinetic studies were carried out on the ATP-protective action against the effects of cooling by adding ATP to lysosomes that had been incubated at 37 degrees C and that were then cooled to 0 degrees C at various times after addition of the ATP. Susceptibility to the effects of cooling continued to decrease until the ATP had been present at 37 degrees C for approximately 3 min before cooling. The concentration of ATP required for maximum initial rates of protection was found to be 10(-3) M or possibly lower. The rate of decrease in susceptibility to the effects of cooling was much slower when ATP was added at 22 than at 37 degrees C, suggesting that enzyme action may be involved in the protective mechanism. Possible mechanisms for the ATP-protective action are discussed.