Superoxide dismutase isozymes in cerebral organoids from autism spectrum disorder patients

Autism spectrum disorder is a pervasive neurodevelopmental disorder with a substantial contribution to the global disease burden. Despite intensive research efforts, the aetiopathogenesis remains unclear. The Janus-faced antioxidant enzymes superoxide dismutase 1-3 have been implicated in initiating oxidative stress and as such may constitute a potential therapeutic target. However, no measurement has been taken in human autistic brain samples. The aim of this study is to measure superoxide dismutase 1-3 in autistic cerebral organoids as an in vitro model of human foetal neurodevelopment. Whole brain organoids were created from induced pluripotent stem cells from healthy individuals (n = 5) and individuals suffering from autism (n = 4). Using Pierce bicinchoninic acid and enzyme-linked immunosorbent assays, the protein and superoxide dismutase 1, 2, and 3 concentrations were quantified in the cerebral organoids at days 22, 32, and 42. Measurements were normalized to the protein concentration. Results represented using medians and interquartile ranges. Using Wilcoxon matched-pairs signed-rank test, an abrupt rise in the superoxide dismutase concentration was observed at day 32 and onwards. Using Wilcoxon rank-sum test, no differences were observed between healthy (SOD1: 35.56 ng/mL ± 3.46; SOD2: 2435.80 ng/mL ± 1327.00; SOD3: 1854.88 ng/mL ± 867.94) and autistic (SOD1: 32.85 ng/mL ± 5.26; SOD2: 2717.80 ng/mL ± 1889.10; SOD3: 1690.18 ng/mL ± 615.49) organoids. Cerebral organoids recapitulate many aspects of human neurodevelopment, but the diffusion restriction may render efforts in modelling differences in oxidative stress futile due to the intrinsic hypoxia and central necrosis.

Microbiota-derived metabolite promotes HDAC3 activity in the gut

The coevolution of mammalian hosts and their beneficial commensal microbes has led to development of symbiotic host-microbiota relationships1. Epigenetic machinery permits mammalian cells to integrate environmental signals2; however, how these pathways are fine-tuned by diverse cues from commensal bacteria is not well understood. Here we reveal a highly selective pathway through which microbiota-derived inositol phosphate regulates histone deacetylase 3 (HDAC3) activity in the intestine. Despite the abundant presence of HDAC inhibitors such as butyrate in the intestine, we found that HDAC3 activity was sharply increased in intestinal epithelial cells of microbiota-replete mice compared with germ-free mice. This divergence was reconciled by the finding that commensal bacteria, including Escherichia coli, stimulated HDAC activity through metabolism of phytate and production of inositol-1,4,5-trisphosphate (InsP3). Both intestinal exposure to InsP3 and phytate ingestion promoted recovery following intestinal damage. Of note, InsP3 also induced growth of intestinal organoids derived from human tissue, stimulated HDAC3-dependent proliferation and countered butyrate inhibition of colonic growth. Collectively, these results show that InsP3 is a microbiota-derived metabolite that activates a mammalian histone deacetylase to promote epithelial repair. Thus, HDAC3 represents a convergent epigenetic sensor of distinct metabolites that calibrates host responses to diverse microbial signals.

DNA Damage Activates TGF-β Signaling via ATM-c-Cbl-Mediated Stabilization of the Type II Receptor TβRII

Activation of both the DNA damage response (DDR) and transforming growth factor β (TGF-β) signaling induces growth arrest of most cell types. However, it is unclear whether the DDR activates TGF-β signaling that in turn contributes to cell growth arrest. Here, we show that in response to DNA damage, ataxia telangiectasia mutated (ATM) stabilizes the TGF-β type II receptor (TβRII) and thus enhancement of TGF-β signaling. Mechanistically, ATM phosphorylates and stabilizes c-Cbl, which promotes TβRII neddylation and prevents its ubiquitination-dependent degradation. Consistently, DNA damage enhances the interaction among ATM, c-Cbl, and TβRII. The ATM-c-Cbl-TβRII axis plays a pivotal role in intestinal regeneration after X-ray-induced DNA damage in mouse models. Therefore, ATM not only mediates the canonical DDR pathway but also activates TGF-β signaling by stabilizing TβRII. The double brake system ensures full cell-cycle arrest, allowing efficient DNA damage repair and avoiding passage of the damaged genome to the daughter cells.

Genetic Manipulation of Human Intestinal Enteroids Demonstrates the Necessity of a Functional Fucosyltransferase 2 Gene for Secretor-Dependent Human Norovirus Infection

Human noroviruses (HuNoVs) are the leading cause of nonbacterial gastroenteritis worldwide. Histo-blood group antigen (HBGA) expression is an important susceptibility factor for HuNoV infection based on controlled human infection models and epidemiologic studies that show an association of secretor status with infection caused by several genotypes. The fucosyltransferase 2 gene (FUT2) affects HBGA expression in intestinal epithelial cells; secretors express a functional FUT2 enzyme, while nonsecretors lack this enzyme and are highly resistant to infection and gastroenteritis caused by many HuNoV strains. These epidemiologic associations are confirmed by infections in stem cell-derived human intestinal enteroid (HIE) cultures. GII.4 HuNoV does not replicate in HIE cultures derived from nonsecretor individuals, while HIEs from secretors are permissive to infection. However, whether FUT2 expression alone is critical for infection remains unproven, since routinely used secretor-positive transformed cell lines are resistant to HuNoV replication. To evaluate the role of FUT2 in HuNoV replication, we used CRISPR or overexpression to genetically manipulate FUT2 gene function to produce isogenic HIE lines with or without FUT2 expression. We show that FUT2 expression alone affects both HuNoV binding to the HIE cell surface and susceptibility to HuNoV infection. These findings indicate that initial binding to a molecule(s) glycosylated by FUT2 is critical for HuNoV infection and that the HuNoV receptor is present in nonsecretor HIEs. In addition to HuNoV studies, these isogenic HIE lines will be useful tools to study other enteric microbes where infection and/or disease outcome is associated with secretor status.IMPORTANCE Several studies have demonstrated that secretor status is associated with susceptibility to human norovirus (HuNoV) infection; however, previous reports found that FUT2 expression is not sufficient to allow infection with HuNoV in a variety of continuous laboratory cell lines. Which cellular factor(s) regulates susceptibility to HuNoV infection remains unknown. We used genetic manipulation of HIE cultures to show that secretor status determined by FUT2 gene expression is necessary and sufficient to support HuNoV replication based on analyses of isogenic lines that lack or express FUT2. Fucosylation of HBGAs is critical for initial binding and for modification of another putative receptor(s) in HIEs needed for virus uptake or uncoating and necessary for successful infection by GI.1 and several GII HuNoV strains.

Qualitative cytological criteria for the validation of enzyme histochemical techniques

Qualitative cytological criteria are concerned with the 'precision' of a histochemical reaction and form part of the general criteria for the validation of enzyme histochemical techniques. Three major problem areas are considered: (a) the general artifacts which interfere with the 'clean' appearance of the tissue sections; (b) the exact intracellular localization of the final reaction product and its relationship to specific subcellular compartments; (c) the problem of diffusion of enzymes or reaction products, or both, from their primary subcellular sites. Each of these points is discussed and illustrated by a few examples and the conclusion is drawn that by careful consideration of various criteria the enzyme cytochemical techniques can provide 'quantitative' information comparable to biochemical measurements of enzyme activity in tissue homogenates. In the example of localization of catalase with 3,3'-diaminobenzidine it is demonstrated that biochemical enzyme assays corrrelate closely with quantitative morphometric data obtained from cytochemical preparations through an automatic image analyser system.

A three-dimensional in vitro model system to study the adaptation of craniofacial skeletal muscle following mechanostimulation

The aim of this study was to investigate the in vitro response of human craniofacial muscle-derived myotubes (primitive/nascent muscle fibres), in three-dimensional constructs, to strain in vitro to mimic clinical scenarios, using expression of the mechanoresponsive gene gelatinase-A/matrix metalloproteinase-2 (MMP-2) as a marker of remodelling of muscle extracellular matrix. Three-dimensional (3D) constructs of cells derived from explants of human masseter muscle (human craniofacial muscle-derived cells; hCMDC) in collagen sponges were subjected to mechanical, uniaxial strain using the Bio-Stretch system. 3D myotube constructs were exposed to the strain regimes of rapid ramp stretch (RRS) or cyclical ramp strain (CRS) with 7.5% and 15% strain. The activity of MMP-2 was assessed by zymography of construct-conditioned medium, whilst lysates of the constructs were used to measure creatine phosphokinase (CPK) activity to confirm the presence of myotubes in the strained constructs. Scanning electron microscopy of the collagen sponges and the CPK assays confirmed the presence of myotubes. MMP-2 was expressed by all the samples and controls, but expression was found to be significantly higher in those cultures strained continuously (RRS), compared to cyclical strain (CRS), and in those strained at 15% compared to 7.5%. Thus, MMP-2 expression, and hence extracellular matrix remodelling, is up-regulated in response to strain and is dependent upon the amount and type of strain to which the muscle is subjected.

Expression of cytochrome P450 enzymes in hepatic organoid reconstructed by rat small hepatocytes

BACKGROUND AND AIMS

Small hepatocytes (SH), which are hepatic progenitor cells, were isolated from an adult rat liver. SH in a colony sometimes change their shape from small to large and from flat to rising/piled-up. The morphological changes of SH may be correlated with hepatic maturation. Cytochrome P450s (CYP) are drug-metabolizing enzymes and the expression is one of hepatic differentiated functions. However, it is well known that the re-expression and maintenance of CYP activity are very difficult in cultured hepatocytes. We investigated the expression of CYP and the enzymatic activities in long-term cultured SH.

METHODS

SH were isolated from adult rat livers and SH colonies were collected, replated on new dishes, and then cultured. CYP1A1/2, CYP2B1, CYP3A2, CYP4A1, and CYP2E1 were induced by the addition of 3-methylcholanthrene, phenobarbital, pregnenolone-16alpha-carbonitrile, clofibric acid, and ethanol, respectively. Immunocytochemistry, immunoblots, and enzyme activities were examined.

RESULTS

SH could differentiate into mature hepatocytes by the addition of Matrigel and re-express constitutive CYPs. The expression of CYP1A1/2, CYP2B1, CYP3A2, and CYP4A1 dose-dependently increased and the amounts gradually increased with time in culture, especially in the cells treated with Matrigel. Activities of CYP1A, CYP2B, CYP3A and CYP2E in SH treated with Matrigel induced by each of the inducers were approximately 120-fold, 2.8-fold, 6.4-fold and 0.8-fold higher than in the control.

CONCLUSION

The matured SH could re-express the constitutive CYP and recover inducibility, not only of protein expression but also of enzyme activities.

Alterations in the expression and localization of protein kinase C isoforms during mammary gland differentiation

Protein kinase C (PKC) is involved in signaling that modulates the proliferation and differentiation of many cell types, including mammary epithelial cells. In addition, changes in PKC expression or activity have been observed during mammary carcinogenesis. In order to examine the involvement of specific PKC isoforms during normal mammary gland development, the expression and localization of PKCs alpha, delta, epsilon and zeta were examined during puberty, pregnancy, lactation, and involution. By immunoblot analysis, expression of PKC alpha, delta, epsilon and zeta proteins was increased in mammary epithelial organoids during the transition from puberty to pregnancy. In mammary gland frozen sections, PKCs alpha, delta, epsilon and zeta were stained in the luminal epithelium and myoepithelium, in varying isoform-and developmental stage-specific locations. PKC alpha was found in a punctate apical localization in the luminal epithelium during pregnancy. During lactation, PKC epsilon was present in the nucleus, and PKC zeta was concentrated in the subapical region of the luminal epithelium. Additionally, marked staining for PKCs alpha, delta, epsilon, and zeta was observed in the myoepithelial cells at the base of ducts and alveoli. This basal ductal and alveolar staining differed in intensity in a developmentally-specific fashion. During most time points (virgin, pregnant, lactating, and early involution), myoepithelial cells of the duct were more intensely stained than those lining the alveoli for PKCs alpha, delta, epsilon and zeta. During late involution (days 9-12), the preferential staining of ducts was lost or reversed, and the myoepithelial cells lining the regressing alveolar structures stained equally (PKCs epsilon and zeta) or more intensely (PKCs alpha and delta), coincident with the thickening of the myoepithelial cells surrounding the regressing alveoli. The increased PKC isoform staining at the base of alveoli during involution suggests that alveolar regression may be influenced by alterations in signaling in the alveolar myoepithelium.

Butyrylcholinesterase regulates laminar retinogenesis of the chick embryo in vitro

During chicken neurogenesis, the sequential expression of butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) between final cell proliferation and differentiation is functionally not understood. Recently, cholinesterases have been shown to regulate neurite growth in vitro. Here, we investigated the effects of inhibition of BChE on laminar histogenesis in retinospheroids that arise from dissociated embryonic chicken retinal cells in rotation culture. In the presence of the BChE inhibitor iso-OMPA (tetraisopropyl pyrophosphoramide), the number of spheroids/dish is increased, and their diameter is decreased by about 20%, corresponding to about 50% volume size. As a corollary, the course of histotypical differentiation is dramatically accelerated. Thus as a consequence of BChE inhibition both, organization of nuclear cell layers and of plexiform-like (neuropile) areas, as detected by an antibody to the fiber fasciculation protein F11, is temporally advanced by at least two days. Moreover, AChE is almost fully diminished in these areas. The results further demonstrate novel roles of cholinesterases during laminar histogenesis of coherent neural networks in vitro.

[An ultracytochemical study of the hydrogenosomes of Trichomonas vaginalis]

The ultracytochemical study of cultural T. vaginalis has been carried out. The activity of magnesium-dependent ATPase, transport (sodium-potassium-dependent) ATPase and adenylate cyclase was detected in dense corpuscles, located on the membranes of hydrogenosomes having a rounded form. The authors suggest that the dense corpuscles are the zones of the active transport of ions through the membranes of hydrogenosomes.

Melanogenic regulatory factors in coated vesicles from melanoma cells

Coated vesicles have been found to contain much higher tyrosinase and gamma-glutamyl transpeptidase activities than premelanosomes. This indicates that similar to tyrosinase, gamma-glutamyl transpeptidase, an enzyme responsible for pheomelanogenesis, is highly concentrated in coated vesicles after its maturation in Golgi associated endoplasmic reticulum (GERL). Furthermore, in the pre- and post-dopaquinone melanogenic pathway, coated vesicles convert dopachrome to colorless indole compounds more quickly than in premelanosomes because of their higher dopachrome conversion factor activity. Melanosomes have been found to exhibit indole conversion factor activity, while coated vesicles show indole blocking factor activity. In moderately tyrosinase-rich premelanosomes, the levels of dopachrome conversion factor and indole blocking factor are lower than in coated vesicles or melanosomes. High levels of indole blocking factor in coated vesicles may indicate why melanin polymer formation does not occur there in vivo despite their high tyrosinase activity.

Inhibition of vacuolar H+-ATPases by fusidic acid and suramin

The vacuolar system of eukaryotic cells is energized by a few ATP-driven ion pumps. One of these, the H+-ATPase, plays a major role in providing the protonmotive force for several organelles, as well as maintaining the proper pH inside the organelles. Formation of the protonmotive force in organelles isolated from the vacuolar system was inhibited by fusidic acid. The inhibition results from a combination of uncoupling the proton pumping and inhibition of the H+-ATPase activity. Suramin is also a potent inhibitor of the H+-ATPase from chromaffin granules. A possible connection between these activities and inhibition of HIV infection is pointed out.

The cDNA sequence of the 69-kDa subunit of the carrot vacuolar H+-ATPase. Homology to the beta-chain of F0F1-ATPases

Vacuolar ATPases constitute a novel class of N-ethylmaleimide- and nitrate-sensitive proton pumps associated with the endomembrane system of eukaryotic cells. They resemble F0F1-ATPases in that they are large multimeric proteins, 400-500 kDa, composed of three to nine different subunits. Previous studies have indicated that the active site is located on the approximately 70-kDa subunit. Using antibodies to the approximately 70-kDa subunit of corn to screen a carrot root lambda gt11 cDNA library, we have isolated cDNA clones of the carrot 69-kDa subunit. The complete primary structure of the 69-kDa subunit was then determined from the nucleotide sequence of its cDNA. The 69-kDa subunit consists of 623 amino acids (Mr 68,835), with no obvious membrane-spanning regions. The carrot cDNA sequence was over 70% homologous with exons of a Neurospora 69-kDa genomic clone. The protein sequence of the carrot 69-kDa subunit also exhibited 34.3% identity to four representative F0F1-ATPase beta-chains over a 275-amino-acid core stretch of similar sequence. Alignment studies revealed several regions which were highly homologous to beta-chains, including sequences previously implicated in catalytic function. This provides definitive evidence that the vacuolar ATPase is closely related to the F0F1-type ATPases. A major functional difference between the 69-kDa and beta-subunits is the location of 3 critical cysteine residues: two in the putative catalytic region (Cys-248 and Cys-256) and one in the proposed Mg2+-binding site (Cys-279). These cysteines (and two others) probably account for the sensitivity of the vacuolar H+-ATPase to the sulfhydryl reagent, N-ethylmaleimide. It is proposed that the two ATPases may have arisen from a common ancestor by the insertion or deletion of a large stretch of nonhomologous sequence near the amino-terminal end of the subunit.

Immunogold determination of amylase concentrations in pancreatic subcellular compartments

We used the immunogold method on ultrathin cryosections to measure intracellular amylase (Am) concentrations in subcellular compartments of rat exocrine pancreatic cells. Previously, the quantitation procedure was characterized in a model system consisting of Am dispersed at known concentration in a matrix of gelatin. Variations in labeling efficiency, due to differences in matrix density, were equalized by embedding in 30% polyacrylamide (PAA). Here we applied these model conditions to rat pancreas and established intracellular Am concentrations [Am]. Specimen blocks were composed of tissue and a reference layer of gelatin mixed with a known Am concentration ([Am]r), both fixed in glutaraldehyde. Cryosections of the PAA embedded blocks were immunogold labeled for Am. The labeling density was measured in the reference layer (LDr) and in structures in exocrine cells that were involved in Am synthesis and transport (LDs). In each of these structures the Am concentration ([Am]s) was calculated from: [Am]s = [Am]r. LDs/LDr In this way we measured average concentrations ranging from 63 mg/ml in rough endoplasmic reticulum to 261 mg/ml in secretory granules. Concentration of Am appeared to occur mainly in the most cis- and the most trans-Golgi cisternae. To check whether sterical hindrance was an inherent bias to the [Am] measurements in compartments that contained high concentrations of the enzyme, the labeling efficiency for Am in intact isolated secretory granules in gelatin and embedded in PAA, was compared with the efficiency when the granules were lysed and approximately 50 times diluted in gelatin before PAA embedment. It appeared that Am was detected with similar efficiency under both conditions. This demonstrated that sterical hindrance did not cause errors in the measurements of cellular Am concentrations.

Studies on the submicrosomal fractions of bovine oligodendroglia: lipid composition and glycolipid biosynthesis

Oligodendroglia were isolated from bovine brain, and a "crude" microsomal fraction obtained from cell homogenates was subfractionated into myelin (MP), plasma membranes (PM), Golgi (GF), smooth (SER) and rough (RER) endoplasmic membranes using discontinuous-sucrose gradient centrifugation. The submicrosomal fractions were characterized by ultrastructural examination and analysis of the specific organelle markers. The myelin and plasma membrane rich fractions contained characteristically the highest amounts of the lipid with lower mole percentages of total phospholipids and phosphatidylcholine, and higher concentrations of phosphatidylethanolamine (+ plasmalogens), cholesterol and galactolipids. Considerable amounts of the typical myelin galactolipids (galacto-cerebrosides, sulfatides and monogalactosyl diglycerides) were also found in the Golgi fraction (GF). The GF fraction had the greatest enrichment of glycolipid-forming galactosyltransferases, and the distribution of these enzymes correlated well with that of the Golgi marker enzymes. The results give evidence that intracellular Golgi apparatus of oligodendroglia is rich in the myelin-specific lipids, and suggest its involvement in the synthesis and processing of myelin lipids.

Solubilization and purification of alpha-mannosidase, a marker enzyme of vacuolar membranes in Saccharomyces cerevisiae

Yeast alpha-mannosidase, a marker enzyme of vacuolar membranes, was solubilized and purified from commercial bakers' yeast. The alpha-mannosidase was solubilized efficiently with 10 mM Na2CO3. A high pH (greater than 8.5) and a sufficient amount of a detergent such as 0.2% (w/v) Triton X-100 were required to keep the enzyme in a soluble state. This suggested that the enzyme is either a peripheral membrane protein or an ecto-type integral membrane protein. After 4,300-fold purification by conventional chromatography, the alpha-mannosidase gave a single band on nondenaturing polyacrylamide gel electrophoresis, but could be fractionated into active isoforms, which consisted of 107-, 73-, and 31-kDa polypeptides, with a Mono Q anion exchange fast protein liquid chromatography system. Apparent molecular weight of the native enzyme was determined as 560,000. It suggested that the composition of isoforms will be described as (107 kDa)n (73 kDa)6-n (31 kDa)6-n, where n is 0-6. The 107- and 73-kDa polypeptides were purified further under denaturing conditions. One-dimensional peptide map analysis and immunological analysis of these polypeptides indicated that they are closely related proteins. Immunoblotting of crude cell lysates revealed that the 107-kDa polypeptide appeared first, and then the 73-kDa polypeptide appeared along growth phase. It suggested that proteolytic conversion of the 107-kDa polypeptide occurs to form the 73- and 31-kDa polypeptides and leads to formation of isoforms of the enzyme.

N,N'-dicyclohexylcarbodiimide-binding proteolipid of the vacuolar H+-ATPase from oat roots

The inhibitor N,N'-dicyclohexylcarbodiimide (DCCD) was used to probe the structure and function of the vacuolar H+-translocating ATPase from oat roots (Avena sativa var. Lang). The second-order rate constant for DCCD inhibition was inversely related to the concentration of membrane, indicating that DCCD reached the inhibitory site by concentrating in the hydrophobic environment. [14C]DCCD preferentially labeled a 16-kDa polypeptide of tonoplast vesicles, and the amount of [14C]DCCD bound to the 16-kDa peptide was directly proportional to inhibition of ATPase activity. A 16-kDa polypeptide had previously been shown to be part of the purified tonoplast ATPase. As predicted from the observed noncooperative inhibition, binding studies showed that 1 mol of DCCD was bound per mol of ATPase when the enzyme was completely inactivated. The DCCD-binding 16-kDa polypeptide was purified 12-fold by chloroform/methanol extraction. This protein was thus classified as a proteolipid, and its identity as part of the ATPase was confirmed by positive reaction with the antibody to the purified ATPase on immunoblots. From the purification studies, we estimated that the 16-kDa subunit was present in multiple (4-8) copies/holoenzyme. The purification of the proteolipid is a first step towards testing its proposed role in H+ translocation.

Proton ATPase in rat renal cortical endocytotic vesicles

To relate ATPase activity to the ATP-driven H+-pump in rat renal endocytotic vesicles we applied an in vitro coupled optical test and a Pi-liberation assay. Endocytotic vesicles contain an ouabain-, vanadate- and oligomycin-insensitive ATPase. The ionophores for K+ and H+, valinomycin and carbonylcyanide p-chloro-methoxyphenylhydrazone (CCCP), respectively, stimulated ATPase activity, indicating its relation to the electrogenic H+-pump. This conclusion is supported by a similar distribution on a Percoll gradient of ATP-driven H+ uptake into endosomes and ionophore-stimulated ATPase activity. Coupled optical and Pi-liberation assays were then used to characterize the H+-ATPase with respect to the requirement for pH, nucleotides, anions, and mono- and divalent cations. The H+-ATPase activity was decreased by widely used blockers: N-ethylmaleimide (NEM), dicyclohexylcarbodiimide (DCCD) and diethylstilbestrol (DES). Different sensitivities to these blockers proved that alkaline phosphatase and H+-ATPase are separate entities. To investigate whether the NEM-, DCCD- and DES-sensitive ATPase activity is confined to intact endocytotic vesicles, cellular membranes from rat kidney cortex were separated on a Percoll density gradient. Surprisingly, endocytotic vesicles contain only a small fraction of the total NEM-, DCCD- and DES-sensitive ATPase activity. The majority of the blocker-sensitive ATPases belongs to membranes of as yet undefined cellular origin.

Characterization and function of catalytic subunit alpha of H+-translocating adenosine triphosphatase from vacuolar membranes of Saccharomyces cerevisiae. A study with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole

Subunit alpha (Mr 89,000) from vacuolar membrane H+-translocating adenosine triphosphatase of the yeast Saccharomyces cerevisiae was found to bind 8-azido[alpha-32P]adenosine triphosphate. Labeling by this photosensitive ATP derivative was saturable with an apparent dissociation constant of 10(-6) to 10(-5) M and decreased in the presence of ATP and ADP. The enzyme was inactivated by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl), with about 1 microM causing half-maximal inactivation in the neutral pH range. This inactivation was prevented by the presence of ATP, ADP, or adenosyl-5'-yl imidodiphosphate (AMP-PNP). The original activity was restored by treating the inactivated enzyme with 2-mercaptoethanol. Kinetic and chemical studies of the inactivation showed that the activity was lost on chemical modification of a single tyrosine residue per molecule of the enzyme. When the enzyme was inactivated with [14C]NBD-Cl, subunit alpha was specifically labeled, and this labeling was completely prevented by the presence of ATP, GTP, ADP, or AMP-PNP. From these results, it was concluded that subunit alpha of yeast vacuolar H+-ATPase has a catalytic site that contains a single, essential tyrosine residue. The kinetics of single site hydrolysis of [gamma-32P]ATP (Grubmeyer, C., Cross, R. L., and Penefsky, H. S. (1982) J. Biol. Chem. 257, 12092-12100) indicated the formation of an enzyme-ATP complex and subsequent hydrolysis of bound ATP to ADP and Pi at the NBD-Cl-sensitive catalytic site. NBD-Cl inactivated the single site hydrolysis and inhibited the formation of an enzyme-ATP complex. Dicyclohexylcarbodiimide did not affect the single site hydrolysis, but inhibited the enzyme activity under steady-state conditions.

Synthesis and assembly of H+-ATPase complex by isolated "rough" thylakoids

The synthesis and assembly of chloroplast H+-ATPase complex were studied by analyzing the incorporation of [35S]methionine into the constituent subunits with isolated intact chloroplasts and with thylakoid membranes that had been prepared from the chloroplasts so that they would retain ribosomes. The complex was isolated from thylakoids after labeling and identified by immunoprecipitation with an antiserum specific to CF1. The mechanism for the assembly of the complex was demonstrated to be active in the isolated chloroplasts by the following observations: the plastid genome-regulated subunits (alpha, beta, epsilon, I, and III) were labeled by in organello translation and recovered with the complex, and three other subunits (gamma, delta, and II) were labeled when intact chloroplasts were incubated with translation products from polyadenylated RNA. The two largest subunits, alpha and beta, were translated on thylakoid-bound ribosomes when the thylakoid membranes were incubated with soluble factors from Escherichia coli. They were recovered with the H+-ATPase complex, suggesting that they are translated on the bound ribosomes in the chloroplast, and that the isolated membranes retain the ability to assemble a complete complex. Provided that these observations are the result of de novo assembly of the complex, the imported and processed nuclear-coded subunits are presumed to be pooled not in stroma but on the membrane.

Localization of acid phosphatase in lamellar bodies of tannic acid treated alveolar type II cells

Acid phosphatase was demonstrated in well preserved lamellar bodies of rats' alveolar type II cells. The highly ordered lamellar organization was preserved by using tannic acid in the tissue procession protocol. Acid phosphatase reaction products were observed in the amorphous regions of the lamellar bodies adjacent to the limiting membranes and in the central core regions. No reaction product was observed in the lamellar areas. 85% +/- 5% of the lamellar bodies were positively reactive, unrelated to their size. Multivesicular bodies were only partially reactive (approx. 50%), except for those attached to lamellar bodies which all had reaction product.

Effect of DL-alpha-difluoromethylornithine on methionine cycle intermediates in Trypanosoma brucei brucei

Activities of enzymes involved in transmethylation reactions were determined in bloodstream trypomastigotes of Trypanosoma brucei brucei infection in rats. S-Adenosyl-L-methionine synthetase (EC 2.5.1.6), S-adenosyl-L-homocysteine hydrolase (EC 3.3.1.1), cystathionine synthase (EC 4.2.1.21), as well as several transmethylases were detected and localized in cytosolic rather than particulate fractions. High performance liquid chromatography analysis of methionine cycle intermediates in cells from untreated rats and from rats treated with the ornithine decarboxylase inhibitor DL-alpha-difluoromethylornithine (DFMO) indicated that the inhibitor causes pronounced changes in concentrations of these intermediates and dramatically alters the methylation index of the cell. These findings demonstrate another in the wide range of metabolite disturbances attributable to DFMO and reflect the belief that multiple biochemical events are a sequel of its action on trypanosomes.

An improved procedure for the isolation of lamellar bodies from human lung. Lamellar bodies free of lysosomes contain a spectrum of lysosomal-type hydrolases

We have recently shown that lamellar body fractions purified from human lung contain a distinct acid alpha-glucosidase distinguishable from lysosomal acid alpha-glucosidase in that it does not cross-react with antibodies raised against the lysosomal enzyme and does not bind to concanavalin A (De Vries, A.C.J., Schram, A.W., Tager, J.M., Batenburg, J.J. and Van Golde, L.M.G. (1985) Biochim. Biophys. Acta 837, 230-238). In order to study the relationship between the non-concanavalin A-binding alpha-glucosidase and lamellar bodies more closely a method was developed for the further purification of the organelles. A purified lamellar body preparation isolated from human lung homogenate by discontinuous sucrose density centrifugation was subjected to gel filtration with Sepharose 4B followed by Percoll density gradient centrifugation, which yielded a lamellar body preparation with a phospholipid phosphorus/protein ratio of 12.57 +/- 0.38 (mumol/mg) (n = 3) as compared to a ratio of 3.34 +/- 0.16 (mumol/mg) (n = 3) in the sucrose density gradient preparation. Concomitantly there was a 3.3 +/- 0.1 (n = 3)-fold enrichment in the content of total acid alpha-glucosidase and a 3.2 +/- 0.1 (n = 3) -fold enrichment of non-concanavalin A-binding acid alpha-glucosidase. The new purification method removes adhering proteins without changing the phospholipid composition. During the successive purification steps the concanavalin A-sensitive and -insensitive alpha-glucosidases remained fully lamellar body fraction associated. Differences between a lysosome-enriched fraction and a lamellar body preparation at varying stages of purification with respect to the ratio between soluble acid hydrolases and the membrane-associated lysosomal enzyme glucocerebrosidase indicate that the purified lamellar bodies were not contaminated with lysosomes. The absence of lysosomes in the purified lamellar body fraction was confirmed by experiments with the weak base glycyl-L-phenylalanine-beta-naphthylamide, which is an artificial substrate for the lysosomal enzyme cathepsin C and brings about lysis of lysosomes. Morphological examination by electron microscopy endorses the absence of contaminating vesicles and organelles and showed a structural integrity of the lamellar bodies in the final preparation. The improved isolation procedure strongly suggests that the concanavalin A-insensitive acid alpha-glucosidase is endogenous to lamellar bodies and supports our earlier idea that it can be used as a lamellar body-specific marker enzyme. In addition, the experiments show that lamellar bodies free of lysosomes contain a spectrum of lysosomal-type enzymes.

Trafficking of lysosomal enzymes

The targeting of lysosomal enzymes from their site of synthesis in the rough endoplasmic reticulum (RER) to their final destination in lysosomes is directed by a series of protein and carbohydrate recognition signals on the enzymes. Lysosomal enzymes, along with secretory and plasma membrane proteins, contain amino-terminal signal sequences that direct the vectorial discharge of the nascent proteins into the lumen of the RER. The three classes of proteins also share a common peptide signal for asparagine glycosylation. The next signal is unique to lysosomal enzymes and permits their high-affinity binding to a specific phosphotransferase that catalyzes the formation of the mannose 6-phosphate recognition marker. This carbohydrate determinant allows binding to specific receptors that translocate the lysosomal enzymes from the Golgi complex to an acidified prelysosomal compartment. There the lysosomal enzymes are discharged for final packaging into lysosomes. Two distinct mannose 6-phosphate receptors have been identified, and cDNAs encoding their entire sequences have been cloned. An analysis of the deduced amino acid sequences of the receptors shows that each is composed of four structural domains: a signal sequence, an extracytoplasmic amino-terminal domain, a hydrophobic membrane-spanning region, and a cytoplasmic domain. The entire extracytoplasmic region of the small receptor is homologous to the 15 repeating domains that constitute the extracytoplasmic portion of the large receptor.

Protease B of the lysosomelike vacuole of the yeast Saccharomyces cerevisiae is homologous to the subtilisin family of serine proteases

The PRB1 gene of Saccharomyces cerevisiae encodes the vacuolar endoprotease protease B. We have determined the DNA sequence of the PRB1 gene and the amino acid sequence of the amino terminus of mature protease B. The deduced amino acid sequence of this serine protease shares extensive homology with those of subtilisin, proteinase K, and related proteases. The open reading frame of PRB1 consists of 635 codons and, therefore, encodes a very large protein (molecular weight, greater than 69,000) relative to the observed size of mature protease B (molecular weight, 33,000). Examination of the gene sequence, the determined amino-terminal sequence, and empirical molecular weight determinations suggests that the preproenzyme must be processed at both amino and carboxy termini and that asparagine-linked glycosylation occurs at an unusual tripeptide acceptor sequence.

[Electron microscopic-cytochemical heterogeneity of succinate dehydrogenase activity in rat cardiomyocytes]

The ultrastructural localization of succinate dehydrogenase in white rat heart myocytes is studied and heterogeneity of reaction products in separate mitochondria and their groups is described. The enzyme activity is cardiomyocyte electron density dependent. This dependence, in all probability, is the result of different structural and functional states of cells and their organelles, that is revealed by electron microscopy as different electron density of these. It is found that middle electron density cells have the maximum enzyme activity. The mechanisms of enzyme activity dependence of cell electron density are discussed.

Immunohistochemical localization of AMP deaminase in rimmed vacuoles in human skeletal muscle

High AMP deaminase reactivity was detected in the rimmed vacuoles in skeletal muscles in adult onset acid maltase deficiency and distal myopathy with rimmed vacuole formation histochemically as well as immunohistochemically. Acid phosphatase activity was positive but myosin ATPase activity was negative in the vacuoles. AMP deaminase found in rimmed vacuoles does not seem to be associated with myosin but is possibly bound to lysosomes or other related organelles in accordance with the proliferation of autophagic vacuoles.

Isolation and nitrogenase activity of vesicles from Frankia sp. strain EAN1pec

Vesicles, specialized cell structures thought to be the site of nitrogen fixation in the actinorhizal bacteria, were isolated from Frankia sp. strain EAN1pec by using French pressure disruption of mycelia followed by differential and isopycnic gradient centrifugation. The isolated vesicles reduced acetylene when incubated anaerobically with Mg2+ ions, ATP, and dithionite. No nitrogenase activity was detected in the disrupted mycelial fractions. Vesicles permeabilized by freeze-thaw or detergents showed increased rates of acetylene reduction due to increased permeability of dithionite. The effect on nitrogenase activity of different ATP concentrations was the same in normal and permeabilized vesicles. The endogenous respiratory rate of vesicles was significantly lower than that of mycelia, and the respiration rate of vesicles did not increase following the addition of succinate. The low respiratory activity of vesicles and their apparent dependence on externally supplied ATP for acetylene reduction suggest that the energy and reducing power for nitrogen fixation may be supplied from the mycelia to which they are attached.

The influence of calcium ions on the adsorption of glycolytic enzymes to cellular structure

In order to provide information on the influence of Ca2+ ions on the adsorption of glycolytic enzymes to cellular structure, the release of these enzymes from digitonized cells has been studied. Increases in the calcium ion concentration were found to cause corresponding decreases in the extent of release of all the glycolytic enzymes, as well as a parallel increase in the extent of polymerization of actin. These observations have been discussed in relation to the effect of physiological concentrations of these ions on the association between glycolytic enzymes and the cytoskeleton.

Characterization of the bioluminescent organelles in Gonyaulax polyedra (dinoflagellates) after fast-freeze fixation and antiluciferase immunogold staining

To characterize the microsources of bioluminescent activity in the dinoflagellate Gonyaulax polyedra, an immunogold labeling method using a polyclonal antiluciferase was combined with fast-freeze fixation and freeze substitution. The quality of the preservation and the specificity of the labeling were greatly improved compared to earlier results with chemical fixation. Two organelles were specifically labeled: cytoplasmic dense bodies with a finely vermiculate texture, and mature trichocysts, labeled in the space between the shaft and the membrane. The available evidence indicates that the dense bodies are the light-emitting microsources observed in vivo. The dense bodies appear to originate in the Golgi area as cytoplasmic densifications and, while migrating peripherally, come into contact with the vacuolar membrane. Mature organelles protrude and hang like drops in the vacuolar space, linked by narrow necks to the cytoplasm. These structural relationships, not previously apparent with glutaraldehyde fixation, suggest how bioluminescent flashes can be elicited by a proton influx from a triggering action potential propagated along the vacuolar membrane. Similar dense bodies were labeled in the active particulate biochemical fraction (the scintillons), where they were completely membrane bound, as expected if their necks were broken and resealed during extraction. The significance of the trichocyst reactivity remains enigmatic. Both organelles were labeled with affinity-purified antibody, which makes it unlikely that the trichocyst labeling is due to a second antibody of different specificity. But trichocysts are not bioluminescent; the cross-reacting material could be luciferase present in this compartment for some other reason, or a different protein carrying similar antigenic epitopes.

Maturation of vacuolar (lysosomal) enzymes in yeast: proteinase yscA and proteinase yscB are catalysts of the processing and activation event of carboxypeptidase yscY

Studies were performed to unravel the activation and maturation mechanism of vacuolar (lysosomal) proteinases in Saccharomyces cerevisiae. In vivo and in vitro studies show that proteinase yscA and proteinase yscB are involved in the activation and processing event of pro-carboxypeptidase yscY. Processing and activation of pro-carboxypeptidase yscY by proteinase yscA depends on an additional factor contained in the vacuolar fraction. Comparable activation can be mimicked by sodium polyphosphate. Optimum pH for processing by this proteinase yscA-triggered event is 5. The proteinase yscA-triggered maturation process of pro-carboxypeptidase yscY leads to an intermediate mol. wt form of the enzyme which is, however, fully active. Proteinase yscB transfers the intermediate mol. wt form of the original precursor to the apparently authentic, mature and active carboxypeptidase yscY. An activation and maturation scheme is devised.

Subcellular distribution of renal tripeptide-releasing exopeptidases active on collagen-like sequences

The rat kidney cortex was found to contain two N-terminal exopeptidases of the tripeptidyl peptidase (TPP) class. Each required a free N-terminus to catalyze the release of collagen-related (Gly-Pro-X) "triplets." In accordance with their apparent pH optima, activities were routinely determined fluorimetrically at pH 4.0 (TPP 4) and at pH 7.0 (TPP 7) on Gly-Pro-Met-2-naphthylamide. The specific activity in both the homogenate and the classical subfractions was much greater at pH 7 than at pH 4. Subfractionation of the microsomal fraction by equilibrium banding in sucrose did not separate the TPP 4 and TPP 7 activities. The banding density (1.18 g/ml) and the distribution patterns for TPP 7 in the microsomal subfractions, and also in the subfractions of the small lysosomes in the mitochondrial-lysosomal (ML) fraction, demonstrate that TPP 7 is associated with smooth membranes. The TPP 4 and TPP 7 activities were clearly separated during subfractionation of the ML fraction. Rate sedimentation demonstrated that TPP 4 was present in the large, fast-sedimenting lysosomes (protein droplets) and in a heterogeneous broad band of smaller lysosomes. Equilibrium banding of the small lysosomes gave two distinct TPP 4-containing populations at densities 1.20 and 1.235 g/ml. Notably, dipeptidyl peptidase II (DPP II) gave identical banding densities and showed distributions very similar to TPP 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme activities in biopsy specimens from large-bowel mucosa in ulcerative colitis

Biopsy specimens from all main segments of the large bowel, obtained from 16 patients with ulcerative colitis, were examined histologically and assayed for a series of organelle marker enzymes. Compared with a control group of 20 subjects, significant dependence on diagnosis was demonstrated for N-acetyl-beta-D-glucosaminidase (p less than 0.01) and monoamine oxidase (p less than 0.05), when dependence on segment was taken into account. Significant correlation with degree of inflammatory cell infiltration was seen in the gamma-glutamyltransferase (p less than 0.0001), 5'-nucleotidase (p less than 0.05), and monoamine oxidase (p less than 0.0001) activities. Patients with dysplasia had lower activity of N-acetyl-beta-D-glucosaminidase (p less than 0.05) than those without dysplasia when evaluated by two-way analysis of variance modified for repeated measurements. Multienzyme analysis could distinguish between specimens with dysplasia and aneuploidy and those without when discriminant analyses were used.

Nonspecific esterase activity expressed in Weibel-Palade bodies of cloned guinea pig aortic endothelial cells

We studied the localization of nonspecific esterase activities in cloned guinea pig aortic endothelial cells using ultrastructural cytochemistry. Weibel-Palade bodies (WPB), which are known to contain von Willebrand protein, were positive for esterase, defining a heretofore unrecognized activity of these organelles. Esterase activity was also found localized to the external surface of the plasma membrane, to cytoplasmic lipid bodies, and to the outer (cytoplasm-facing) surface of certain membrane-bound cytoplasmic vacuoles. Localization of esterase activity to these four discrete sites probably reflects the presence of a number of endothelial cell enzymes capable of hydrolyzing alpha-naphthyl acetate or butyrate. The physiological substrate and biological function of these enzyme activities are not presently understood.

The effects in the excess administration of prostaglandin E1 on the indicator enzymes of organella membrane in gastric mucosa

Administration of excess vitamin A to rats causes gastric ulceration. In this study the effects on the gastric mucosa of excess vitamin A and excess prostaglandin E1, alone and in combination, were studied. Prostaglandin E1 protected against ulceration by vitamin A. Vitamin A labilized marker enzymes from four different membrane systems, namely those of the lysosomes, mitochondria, endoplasmic reticulum and plasma membrane, whereas only the effect on lysosomes was prevented by prostaglandin E1. Indeed, the prostaglandin alone labilized the enzymes from plasma membrane and endoplasmic reticulum and also damaged mitochondrial membranes. Both vitamin A and prostaglandin E1 caused a reduction in the total number and an increase in irregularly-shaped mitochondria in the parietal cells and produced dilation of the endoplasmic reticulum in both parietal and chief cells. It is noteworthy that prostaglandin E1 effectively prevents ulceration by vitamin A despite the extent to which it damages these membrane systems. These findings lend support to the hypothesis that vitamin A ulceration of the gastric mucosa is mediated via release of lysosomal enzymes, following damage to the lysosomal membranes.

ATPase of basal bodies of Tetrahymena pyriformis

The Ca2+-ATPase activity in basal bodies of Tetrahymena pyriformis was determined by cytochemical and biochemical methods. It was found that the sites of the Ca2+-ATPase activity are associated with the basal body microtubules. A method for the isolation of the basal bodies in a purified form in amounts for biochemical assay has been developed. Some properties of basal body ATPase were examined. It was established that the enzyme activity is specific for the hydrolysis of ATP and deoxy-ATP. The characteristic behaviour of the ATPase activity in response to divalent cations was assessed: the enzyme is stimulated by Ca2+ and inhibited by Mg2+. Basal body ATPase has a pH optimum of 7.5. Electrophoretic analysis of the protein composition of basal bodies revealed proteins with molecular weights of 56 and 43 kDa, corresponding to those of tubulin and actin respectively. It is suggested that the basal body ATPase may be involved in beating of the cilia, participating in the mechanochemical processes needed for motility of Tetrahymena pyriformis.

Protein sorting in yeast: the localization determinant of yeast vacuolar carboxypeptidase Y resides in the propeptide

We have isolated cis-acting mutations in the gene encoding the yeast vacuolar protein carboxypeptidase Y (CPY) that result in missorting and aberrant secretion of up to 95% of newly synthesized CPY. The CPY polypeptides synthesized by these mutants use the late secretory pathway to exit the cell, since the late-acting sec1 mutation prevents their secretion. The mutant versions of CPY are secreted as the proCPY zymogen and are enzymatically activatable in vivo and in vitro. All the mutations, including small deletions and an amino acid substitution, map to the amino-terminal propeptide region and define a discrete yeast vacuolar localization domain whose integrity is required for efficient sorting of the CPY zymogen. Thus, the N-terminal propeptide of CPY carries out at least three functions: it mediates translocation across the endoplasmic reticulum, renders the enzyme inactive during transit, and targets the molecule to the vacuole.

Distinct sequence determinants direct intracellular sorting and modification of a yeast vacuolar protease

We have mapped a sequence determinant in the vacuolar glycoprotein carboxypeptidase Y (CPY) that directs intracellular sorting of this enzyme. Through the study of hybrid proteins, consisting of amino-terminal segments of CPY fused to the secretory enzyme invertase, we have found that the N-terminal 50 amino acids of CPY are sufficient to direct delivery of a CPY-Inv hybrid protein to the yeast vacuole. Our data suggest that this 50 amino acid segment of CPY contains two distinct functional domains; an N-terminal signal peptide followed by a segment of 30 amino acids that contains the vacuolar sorting signal. Deletion of this putative vacuole sorting signal from an otherwise wild-type CPY protein leads to missorting of CPY. Furthermore, examination of the Asn-linked oligosaccharides present on CPY and CPY-Inv hybrid proteins suggests that an additional determinant in CPY specifies the extent to which these proteins are glycosylated in the Golgi complex.

[Effect of a NaCl gradient on the transport of para-aminohippuric acid into the vesicles of the basolateral membrane of the kidney cortex]

Basolateral membrane vesicles were isolated from the rat kidney cortex by a modified method of cation precipitation. Different steps of preparation were analysed using the marker enzymes: Na+,K+-ATPase (for basolateral membrane), alkaline phosphatase (for apical membrane), glucose-6-phosphatase (for membranes of endoplasmic reticulum) and succinate dehydrogenase (for mitochondria). The basolateral membrane was purified by a 8-9-fold treatment with Na+,K+-ATPase, while other membrane contaminations were as low as 2% (as compared to homogenate). The transport of 3H-p-aminohippurate (3H-PAH) by basolateral membrane vesicles was measured under different experimental conditions. The 3H-PAH uptake was found to be Na-gradient dependent. The initial rate of 3H-PAH uptake in the presence of NaCl gradient (500 pM/mg X min) was higher than without the gradient (88 pM/mg X min). It is concluded that the PAH transfer across the basolateral membrane may be energized by the Na+ chemical gradient.

Increased degradation in rat liver induced by antilipolytic agents: a model for studying autophagy and protein degradation in liver?

A dramatic increase in the plasma glucagon/insulin ratio can be induced by treating fasted rats with antilipolytic drugs (e.g., with 3,5-dimethylpyrazole, 12 mg/kg body wt). These hormone changes are the physiologically appropriate response to a rapid decrease in free fatty acids and glucose plasma levels. Under this experimental condition, many vacuolated lysosomes can be observed at the electron microscopic level as early as 30 min and autophagic vacuoles are detectable in the liver cells 1 hr after the administration of the drug. By 1 hr and 45 min, vacuoles often contain recognizable peroxisomes. At the biochemical level, liver proteolysis in vitro is increased significantly. Very interestingly, changes in peroxisomal (but not mitochondrial or reticulum or cytosolic) enzyme activities are detected that are preventable by the administration of glutamine (i.e., of an inhibitor of proteolysis in vivo) but not by an isocaloric amount of glycine or alanine. It is concluded that the administration of antilipolytic agents to fasted animals may provide a convenient (i.e., an inexpensive, highly reproducible and timable) physiologic model to study hormone-induced autophagy in liver cells.

Accessibility of Trypanosoma brucei procyclic glycosomal enzymes to labeling agents of various sizes and charges

The high efficiency of glycolysis in Trypanosoma brucei has been attributed to impermeability of the glycosomal membrane to most metabolites. However, the strong stimulation of the glycolytic rate by exogenous metabolites and coenzymes in intact glycosomes is only compatible with their accessibility to the internal space. The accessibility of glycosomal enzymes to protein labeling agents of varying charge and size has been investigated. The results show that the glycosomal membrane is permeable to small molecules of the size of metabolites, but impermeable to larger molecules.

Phospholipase A2 activity in prostasomes from human seminal plasma

Phospholipase A2 (PLA2) activity was measured and partially characterized in prostasomes isolated from human seminal plasma. The results show high PLA2 activity in seminal plasma with a threefold enrichment in the isolated prostasomes. Highest activity was found at pH 8.0 and 10.5, and there was an absolute requirement for calcium with almost total inhibition of PLA2 activity in the presence of 1 mM EDTA. Analysis with two-dimensional gel electrophoresis of prostasome material revealed a complex protein pattern with most of the proteins in the molecular weight interval of 10,000-90,000 daltons. The possible role of PLA2 in prostasomes is discussed.

Hydrogenosomal ATP:AMP phosphotransferase of Trichomonas vaginalis

1. ATP:AMP phosphotransferase (adenylate kinase) is present in Trichomonas vaginalis, primarily with hydrogenosomal localization. 2. Adenylate kinase has been purified from hydrogenosome-enriched fractions by solubilization with Triton X-100 and KCl followed by affinity chromatography and gel filtration. 3. The enzyme has a Mr = 28,000, a broad pH optimum of pH 7-9, requirement for Mg2+ and specificity for adenine and deoxyadenine nucleotides. 4. The activity is competetively inhibited by P1,P5-di(adenosine-5') pentaphosphate (Ki 200 nM) and reversibly inactivated by 5,5'-dithiobis-(2-nitrobenzoate). 5. Catalytic properties of this enzyme are similar to those of enzymes from other organisms. Other properties indicate its uniqueness, however, since its molecular mass and Ki for P1,P5-di(adenosine-5'-)-pentaphosphate bring it closer to the mitochrondrial isoenzyme, while it shares a requirement for reduced thiol groups with the cytosolic isoenzyme.

The proton pump ATPase of lysosomes and related organelles of the vacuolar apparatus

In this review, I hope to achieve the following: (a) to document the presence of a lysosome-like proton pump ATPase in many different membrane systems of animal, plant and microbial origin; (b) to glean from the diverse data common characteristics of these ATPases, especially as regards their similarities and differences with mitochondrial-type F1F0 proton pump ATPases; and (c) to consider questions of synthesis and regulation of a cellular proton pump system with such a widespread distribution.

Electrically neutral Na+-H+ exchange in endosomes obtained from rabbit renal cortex

Endocytotic vesicles (i.e., endosomes) were prepared from rabbit renal cortex following the intravenous injection of horseradish peroxidase. The endosomal population was derived from a 100,000-g pellet and was found at equilibrium in the lightest area of a sucrose density gradient. This population was separate from other organelles as determined by enzyme markers and had a 2.5-fold enrichment of horseradish peroxidase specific activity compared with the homogenate specific activity corrected for soluble horseradish peroxidase activity. The endosomes contain an oligomycin-insensitive, electrogenic H+-translocating ATPase. They also contain an electroneutral Na+-H+ exchanger. This exchanger is not inhibited by amiloride, and lithium is not a substrate for the exchanger. Lithium does inhibit the Na+-H+ exchanger when added prior to the addition of sodium. The Michaelis constant for sodium of the endosomal Na+-H+ exchanger was found to be 10.0 mM. These data indicate that a population of endosomes from rabbit renal cortex contain an electrogenic H+-ATPase and an electroneutral Na+-H+ exchanger and that the exchanger is distinct from the brush-border membrane Na+-H+ antiporter.

[Activity of organelle-specific enzymes in rat organs during consumption of different amounts of protein]

Activity of enzymes from mitochondrial plasmatic membranes, lysosomes, peroxisomes and endoplasmic reticulum was studied in rat liver, kidney, spleen tissues and blood serum under various conditions of protein consumption. Excess of protein, up to 36%, did not affect distinctly the activity of the enzymes studied, whereas specific reactions of lysosomal and peroxisomal enzymes, which were especially distinct in liver tissue, were found in response to protein deficiency (4%). The data obtained suggest the possible functional interrelationship between the enzymatic systems of lysosomes and peroxisomes under conditions of adaptation to protein deficiency.