Phosphomannosyl-enzyme receptors in rat liver. Subcellular distribution and role in intracellular transport of lysosomal enzymes

beta-Hexosaminidase B purified from human fibroblast secretions was used as a ligand to study phosphomannosyl-enzyme receptors in membranes from rat tissues. Enzyme binding to rat liver membranes was saturable, competitively inhibited by mannose 6-phosphate, not dependent on calcium, and destroyed by prior treatment of the hexosaminidase with either alkaline phosphatase or endoglycosidase H. Most (90%) of the phosphomannosyl-enzyme receptors were found in endoplasmic reticulum, Golgi apparatus, and lysosomes; 9.5% in the plasma membrane, and less than 1% in nuclei and mitochondria. Receptors were vesicle-enclosed in all fractions except plasma membrane. Receptors in the endoplasmic reticulum apparently were occupied by endogenous ligands, but most receptors in lysosomes and plasma membrane were unoccupied. Most of the endogenous beta-hexosaminidase was in lysosomes and was released from vesicles by detergent treatment. Displacement of the residual receptor-bound endogenous beta-hexosaminidase (mostly in endoplasmic reticulum and Golgi apparatus) from detergent-treated membranes by mannose 6-phosphate released high uptake enzyme with properties expected for phosphomannosyl-enzymes. Mannose 6-phosphate-inhibitable enzyme receptor activity was found in nine rat organs and correlated roughly with their lysosomal enzyme content. These data support a general model for lysosomal enzyme transport in which the phosphomannosyl-enzyme receptor acts as a vehicle for delivery of newly synthesized acid hydrolases from the endoplasmic reticulum to lysosomes.

The ribosome binding sites recognized by E. coli ribosomes have regions with signal character in both the leader and protein coding segments

Oligonucleotide analysis, by a novel computerized procedure, was first applied to determine the sequence of an ideal E. coli promoter (Scherer et al., Nucl. Acids Res. 1978, 5:3759-3773) and has now been used to obtain the sequence of nucleotides that should be present in a messenger RNA for optimum binding to the E. coli ribosome. This sequence is: UU.UUAAAAAUUAAGGAGGUAUAUUAUGAAAAAAAUUAAAAAACUCAA AA U A AUA A CUC G. Comparison of this sequence with each of the 68 ribosome binding site sequences used to generate it shows a preference rather than an absolute requirement for a specific base in any given position. The preference for certain bases persists along the whole length of the RNA within the ribosome binding domain even though nearly half of that length includes translated codons. Thus messages without leader sequences (like lambda CI mRNA) can still have some affinity for the ribosome. Part of the model sequence is complementary to the 3'end of 16S rRNA.

Cytochemical demonstration of NADH-ferricyanide reductase and nucleoside diphosphatase activities in dictyosome-like structures of guinea pig spermatocytes

Structures superficially resembling dictyosomes of Golgi apparatus are present in guinea pig spermatocytes and in spermatids in late stages of development. They coexist with Golgi apparatus. In this report, we demonstrate that the dictyosome-like structures (DLS) and Golgi apparatus share cytochemical "markers", inosine diphosphatase and thiamine pyrophosphatase. Additionally, the cytochemical marker for the mature face of conventional Golgi apparatus as well as most plasma membranes, a glutaraldehyde-resistant NADH-ferricyanide reductase, is present in DLS. The latter reaction is also given by the membranes of the acrosome and that portion of the conventional Golgi apparatus (i.e., the thick cisternae) presumed to be responsible for acrosome formation. A distinguishing feature between DLS and Golgi apparatus is in the distribution of reaction product. Golgi apparatus reaction product is concentrated toward one face of each dictyosome while DLS reaction product is usually randomly distributed across the stacks.

Ganglioside biosynthesis in rat liver: alteration of sialyltransferase activities by nucleotides

CMP-NAcNeu:GM3 ganglioside sialyltransferase (GD3 synthase) was characterized with respect to regulation of activity by nucleotides and compared in this regard with other sialyltransferases of ganglioside biosynthesis. Nucleotides preferentially inhibited the activity of GD3 synthase. Di- and trinucleotides inhibited most strongly and cytidine nucleotides were the most inhibitory class. The mode of inhibition by CMP (competitive or noncompetitive) varied with storage conditions of Golgi apparatus membranes; CMP inhibition was decreased during a series of consecutive freeze-thawings of membranes. Also, GD3 synthase inhibition by CDP was only partially relieved by excess Mg2+. With lactosylceramide as the in vitro precursor, synthesis of GM3 was always less inhibited by cytidine nucleotides than was that of GD3 and GT3. An 8-fold reduction in the ratio GD3/GM3 in the reaction products was obtained at 1.5 mM CTP. Separate incubations for the sialylation of GM3 or GM1 showed cytidine nucleotides increased synthesis of GD1a relative to GD3 by 3.5-fold.

Ganglioside biosynthesis in rat liver: characterization of cytidine-5'-monophospho-n-acetylneuraminic acid:hematoside (GM3) sialyltransferase

CMP-NAcNeu:GM3 ganglioside sialytransferase (GD3 synthase) was concentrated 80-100-fold, relative to total homogenates, in Golgi apparatus fractions from rat liver. Ultrasound treatment of Golgi apparatus in a low salt medium extracted 40-60% of the original protein but did not dissociate the transferase from membranes. The acivity was greatest in the presence of certain detergents, had a pH optimum of 6.2, was stimulated by mg2+ and diacylphospholipids and was inhibited by lysophospholipids. Apparent Km values for CMP-NAcNeu and GM3 were about 0.8 and 0.2 mM, respectively. On chromatographic separation, virtually all the reaction product migrated as GD3. GD3 synthase appeared to be a glycoprotein since the activity bound to concanavalin A-Sepharose and was eluted, with increased specific activity, by alpha-methyl mannoside.

Characteristics of transplantable tumors induced in the rat by N-2-fluorenylacetamide: elevations in tissue and serum sialic acid

The correlation between levels of sialic acid and sialic acid-containing glycolipids (gangliosides) in tumors and serum with the growth characteristics of the tumors was investigated in transplantable hepatomas and squamous cell carcinomas initiated with the carcinogen N-2-fluorenylacetamide and propagated in vivo and in tissue culture. Tumor lines varied in histologic classification, growth rate, and ability to form pulmonary metastases. There was neither a correlation between growth rate and histologic classification nor between either of these two parameters and the ability to metastasize. Total and ganglioside sialic acid levels were elevated in carcinogen-treated liver and in transplantable hepatomas when contrasted with normal liver. Levels of sialic acid showed a weak correlation with the growth rate of hepatomas. Gangliosides from nonmetastatic hepatoma lines exhibited less N-acetylneuraminic acid--galactose--glucose-N--acylsphingosine (GM3) and an increased ratio of total monosialogangliosides to disialogangliosides than did metastatic lines. Ganglioside patterns of metastatic hepatoma lines more closely resembled the ganglioside patterns of normal liver than did those of the nonmetastatic lines. Concomitant elevations of total and ganglioside sialic acid levels were observed in sera of animals bearing subcutaneous implants. Serum levels of total sialic acid did correlate with total sialic acid levels found in the tumor tissues. The levels of serum sialic acid were not correlated directly with levels of serum sialyltransferase activity. Elevations of both tissue and serum ganglioside sialic acid were consistent features of liver tumorigenesis in the rat after N-2-fluorenylacetamide administration. They appeared, furthermore, to be early events not directly related to tumor cell differentiation or metastasis.

Identification of etioplast membranes in fractions from soybean hypocotyls

Three independent methods, one cytological and two biochemical, were used to estimate contributions of plastids and plastid fragments to various membrane fractions. In thin sections viewed by electron microscopy, KMnO(4) selectively enhanced the images of plastid membranes in situ as well as in isolated fractions. The amounts of plastid fragments in isolated membrane fractions were determined by electron microscopic morphometry of fractions fixed with KMnO(4) in conjunction with analysis of galactolipids and carotenoids. Monogalactosyl and digalactosyl diglyceride contents were directly correlated with the amount of plastid membranes in the fractions identified by electron microscope morphometry. Amounts of carotenoids also correlated with plastid membranes except at very low levels where estimates based on carotenoids exceeded those based on morphometry.

Distribution of insulin receptors among mouse liver endomembranes

Specific binding of insulin to highly purified preparations of rough endoplasmic reticulum, Golgi apparatus, and plasma membrane of mouse liver was determined. 125I-labeled insulin bound maximally to the plasma membrane in radio-receptor assays. Golgi apparatus fractions exhibited binding 10--20% that of plasma membrane and rough endoplasmic reticulum exhibited only 1--2% of plasma membrane binding. Binding was proportional to membrane concentration and dose vs. response curves were very similar for the different fractions. Scatchard analysis of the insulin binding data for the plasma membrane and Golgi apparatus fractions showed curvilinear plots yielding similar apparent binding affinities (0.9 and 3.0-10(8) M-1, respectively). Purity of the isolated endomembranes was analyzed by morphometry and (Na+ + K+ + Mg2+)-ATPase and these preparations displayed less than 1% contamination by plasma membrane. These findings provide important confirmation of the presence of insulin receptors in Golgi apparatus membranes comparable to those located on the plasma membrane. Finally, the present study did not allow us to verify the existence of insulin receptors in the endoplasmic reticulum.

Calcium uptake by sarcoplasmic reticulum of rat muscle: inhibition by DDT

Sarcoplasmic reticulum fragments capable of accumulating calcium were isolated from rat skeletal muscle by differential and sucrose gradient centrifugation. The ability of these fragments to accumulate calcium was impaired by adding 2,2-bis-(p-chlorophenyl)-1,1,1-trichloroethane (DDT) to the assay medium at concentrations of 0.06 to 6 muM. DDT (6 muM) caused a sharp lag in calcium uptake, with an 82% reduction in reaction rate 30 sec after calcium was added and a 62% reduction after one min. Basal ATPase activity of the microsomal fraction was inhibited by DDT but the calcium-stimulated increment of ATP hydrolysis was not. The findings show that DDT hinders calcium uptake by sarcoplasmic reticulum, but by some means other than inhibition of the calcium-stimulated ATPase. An apparent antagonism between DDT and ouabain or oligomycin was indicated. We propose that the presence of the lipid-soluble DDT molecule within the membrane of the sarcoplasmic reticulum interferes with the normal rapid uptake of calcium ions required for muscle relaxation, and that this interference may contribute to loss of muscle control in organisms poisoned by DDT.

Lipoprotein secretion by rat liver Golgi apparatus. Lipoprotein particles and lipase activity

Lipoprotein particles of the size range of very low density lipoproteins in smooth endoplasmic reticulum, peripheral elements of the Golgi apparatus, and secretory vesicles of the immature Golgi apparatus face are 55 to 80 nm in diameter. Particles in mature secretory vesicles are smaller (45 nm). Concomitant with the change in particle size, the lumina of mature vesicles increase in electron density. A technique to fractionate immature and mature secretory vesicles was based on precipitation of a cupric-ferrocyanide complex (Hatchett's brown) through the action of a NADH-ferricyanide oxido-reductase resistant to glutaraldehyde which is characteristic of the membranes of mature secretory vesicles and of the plasma membrane of liver. Mature secretory vesicle fractions so isolated were enriched in cholesterol and depleted in triglycerides relative to immature vesicles on a phospholipid basis. Lipase activity was present in secretory vesicle fractions of the Golgi apparatus as shown by biochemical analysis and by cytochemistry. Cytochemical studies showed lipase to be present in both mature and immature vesicles but most evident in immature vesicles. The findings suggest that some very low density lipoprotein particles are converted to particles of smaller diameter during transit through Golgi apparatus. A lipase-mediated hydrolysis of triglycerides may relate to the transformation.

B-type cytochromes in plasma membranes isolated from rat liver, in comparison with those of endomembranes

Fractions of plasma membranes, Golgi apparatus, endoplasmic reticulum (ER), and nuclear envelope were isolated from rat liver and were characterized by electron microsocpe and biochemical methods. The purity of the fractions was controlled by morphometry and by marker enzyme activities. Amounts of cytochromes b5, P-450, and P-420 were measured, as well as the NADPH- and NADPH-cytochrome c reductase activities. The pigments of the microsomal electron transport system were found in all membrane fractions in relatively high amounts, thus excluding an origin by microsomal contamination. Purified preparations of plasma membrane and Golgi apparatus contained approximately 30% of the cytochrome b5 and cytochrome P-450 + P-420 found in ER membranes. Plasma membranes were also characterized by a high ratio of P-420/450. Degradation of cytochromes P-450 and P-420 was relatively rapid in all fractions, except in the ER. Cytochrome b5 extracted from plasma membranes was spectrophotometrically and enzymatically indistinguishable from ER cytochrome b5. However, immunnlogical characterization with rabbit antibodies against the trypsin-resistant core of microsomal cytochrome b5 showed the presence of at least two types of cytochrome b5 in ER membranes, in contrast to the plasma membranes in which only one of these components was detected. This immunological differentiation also demonstrates that the plasma membrane-bound cytochrome b5 is endogenous to this membrane and does not reflect contamination by ER elements. We conclude that cytochromes b5, P-450, and P-420 are not confined only to ER and nuclear membranes but also occur in signficant amounts in Golgi apparatus and plasma membranes. The findings are discussed in relation to observations of similar redox components in Golgi apparatus, secretory vesicles, and plasma membranes of other cells.

Ganglioside patterns of metastatic and non-metastatic transplantable hepatocellular carcinomas of the rat

In previous investigations, we correlated levels of sialic acid, gangliosides, and ganglioside glycosyltransferases with tumorigenesis over a 24-week continuum of growth of hepatocellular neoplasms of the rat induced by the carcinogen N-2-fluorenylacetamide. However, metastatic tumors developed only rarely and were not analyzed. To investigate surface changes associated with metastasis, well-differentiated and poorly differentiated hepatocellular carcinomas were transplanted to syngeneic recipient rats. From those, several metastatic and nonmetastatic isolates were obtained and compared. Both total and ganglioside sialic acid amounts in transplantable hepatomas were elevated above control liver values but were significantly lower for metastatic lines than for nonmetastatic lines. The nonmetastatic lines were characterized by ganglioside patterns depleted in the precursor ganglioside GM3 (sialic acid-galactose-glucose-ceramide) and elevated in the products of the monosialoganglioside pathway. In contrast, metastatic isolates exhibited a restoration of GM3 and nearer normal amounts of other gangliosides. The findings point to differences in sialic acid-containing glycolipids, comparing metastatic and nonmetastatic hepatocellular carcinomas, and further extend the concept that ganglioside alterations do not cause tumorigenesis but are the end result of a cascade of events which apparently continue beyond the onset of metastasis.

Action and Inhibition of Endogenous Phospholipases during Isolation of Plant Membranes

Endogenous phospholipase D and phosphatidic acid phosphatase activities were demonstrated in membrane fractions isolated from soybean (Glycine max L.) hypocotyls. Phospholipase D activity was distributed widely among different membrane fractions while phosphatidic acid phosphatase was found predominantly in membranes equilibrating in lower sucrose densities. Phospholipase D action was unaffected by ethylenediaminetetraacetic acid, sodium salt or ethylene glycol-bis(beta-aminoethyl ether)-N,N'-tetraacetic acid but was prevented by a mixture of 4% choline and 4% ethanolamine. Phosphatidic acid phosphatase was inhibited by 10 millimolar glycerol 1-phosphate or by homogenization media prepared with coconut milk as a solvent instead of water. Under fully protected conditions the phospholipid composition of soybean membrane fractions remained unchanged for at least 1 hour at 20 C. Membranes prepared under protected conditions had low phosphatidic acid contents and the phospholipid compositions closely resembled those of corresponding animal membranes.

Cytochemical demonstration of glutaraldehyde-resistant NADH-ferricyanide oxido-reductase activities in rat-liver plasma membranes and Golgi apparatus

NADH-ferricyanide reductase activity was demonstrated in rat liver endomembranes by cytochemical procedures. The activity observed in plasma membrane and mature portions of the Golgi apparatus resisted fixation in 0.1% glutaraldehyde, a characteristic which permitted differentiation of the NADH-ferricyanide reductase of plasma membranes and mature Golgi apparatus elements from those of mitochondria, microbodies, endoplasmic reticulum and nuclear envelope. With the latter membranes, activity could be demonstrated only with unfixed material or following brief glutaraldehyde fixation and was greatest with broken cells or isolated fractions due to problems of penetration of reagents. Biochemical studies paralleled cytochemical findings with respect to glutaraldehyde fixation and sensitivity to other metabolic inhibitors. The findings provide evidence that a NADH-ferricyanide reductase may be among the membrane constituents conserved and/or modified during flow differentiation of membranes. The basis for a method to evaluate plasma membrane contamination of endoplasmic reticulum fractions and to differentiate among mature and immature secretory vesicles of the Golgi apparatus is also indicated.

Structural differences contrast higher plant and animal Golgi apparatus

The intercisternal spacings between cisternae of dictyosomes of higher plants differ from those of mammalian dictyosomes. In plants, the spacings increase from an average of about 8.0 nm at the forming face to about 14.0 nm at the maturing face. The increase in spacing coincides with the appearance within the intercisternal space of parallel filaments called intercisternal elements. In mammals, the intercisternal spacings are more nearly constant, and intercisternal elements have not been observed. Plant and animal dictyosomes may differ as well in the relative widths of the cisternal lumina, the widths of the intercisternal spacings, and in more subtle ways involving the appearance of the membranes. These structural differences may be indicative of some functional differences that contrast higher plant and animal Golgi apparatus.

Serum sialic acid levels increased in tumor-bearing dogs

Serum concentrations of lipid-soluble (glycolipid) sialic acid were determined for 96 client-owned dogs, of which 24 were diagnosed as bearing tumors. A markedly increased concentration of lipid-soluble serum sialic acid was found in 22 of 24 tumor-bearing dogs (92%) compared with 17 of 72 dogs with other definitely false-positive, based on necropsy and follow-up work. Almost all others had acute infections or terminal congestive disorders and were potential tumor bearers. The values obtained appeared to be independent of the sex or age (or both) of the dogs. Based on the analysis of a single biochemical variable, the procedure may permit cancer detection applicable to a wide range of tumor types in dogs if evaluated in terms of the general health status of the animal.

Nature of the phosphotungstic acid-chromic acid (PACP) stain for plasma membranes of plants and mammalian sperm

The selective staining of plasma membranes of plants and porcine spermatozoa given by a mixture consisting of 1% phosphotungstic acid in 10% chromic acid (PACP) applied following periodic acid destaining of glutaraldehyde-osmium tetroxide-fixed electron microscope sections is reduced or eliminated by prior extraction of the tissues with lipid solvents, including ethanol. The ethanol-soluble fraction of sperm contains constituents which restore the PACP-staining reaction when added to ethanol-extracted and lyophilized sperm. Analysis of the ethanol extracts by thin layer chromatography revealed two major components which reacted with both phosphotungstic acid (PTA) and alpha-naphthol detection reagents. These PTA-positive constituents were concentrated in plasma membranes of sperm; components with similar mobilities were found in fractions of plasma membranes from plants. Addition of the PTA-positive constituents from either sperm or plants to extracted and lyophilized sperm restored the PACP staining. The findings are interpreted to mean that one or more low molecular weight constituents (saccharides or glycolipids), rather than glycoproteins, concentrated in plaslma membranes are responsible for the unique PACP staining in both plants and porcine sperm.

Distribution of adenylate cyclase among membrane fractions of rat liver

Adenylate cyclase activity was detected in plasma membranes, Golgi apparatus, and endoplasmic reticulum from rat liver. Adenylate cyclase activities of purified membranes were determined biochemically by two methods. In one, the synthesis of radioactive cyclic AMP from ATalpha32P was monitored. In the other, the synthesis of cyclic AMP was quantitiated using a protein which specifically binds cyclic AMP. The enzyme activity was responsive to activation by both glucagon and sodium fluoride although differences in degree of activation were noted comparing plasma membrane, Golgi apparatus, and endoplasmic reticulum. Cytochemical studies, using both whole tissue and purified cell fractions and conducted in parallel, confirmed the biochemical results. Deposition of lead phosphate, enhanced by glucagon and NaF with samples incubated with appropriate substrates, was not restricted to plasma membranes of hepatocytes but was present in intracellular membranes as well. Adenylate cyclase of rat hepatocytes appears more widely distributed among internal membranes than previously recognized.

Gangliosides of liver tumors induced by N-2-fluorenylacetamide. I. Ganglioside alterations in liver tumorigenesis and normal development

Hyperplastic nodules and hepatocellular carcinomas were induced in livers of rats by a low-protein diet containing 0.05% of the carcinogen N-2-fluorenylacetamide. Ganglioside amounts and composition were determined for histologically different hepatocellular carcinomas and compared with those for control livers, hyperplastic nodules, and liver tissue surrounding hepatomas and nodules as well as those for livers of fetal, newborn, 1-week-old, weanling, and adult Sprague-Dawley rats. Ganglioside sialic acid levels were elevated above those of normal adult liver in all liver tissues following the carcinogen treatment regimen. Livers of fetal and newborn rats contained nearly twice the amount of ganglioside sialic acid on a protein or DNA basis as did livers of adult rats. Analyses of individual nodules and hepatomas revealed two populations of tumors in which the levels of ganglioside sialic acid were 2.3 and 3.8 times normal. Ganglioside sialic acid content was at hepatoma levels in small nodules. Individual gangliosides were evenly distributed between products of the monosialoganglioside and disialoganglioside pathways in normal liver with a ratio of [N-acetylneuraminic acid (sialic acid)] (NAN)-galactose (Gal)-N-acetylgalactosamine (GalNAc)-(NAN)-Gal-glucose (Glc)-ceramide (Cer) (GD1a) to Gal-GalNAc-(NAN)2-Gal-Glc-Cer (GD1b) of about one. In contrast, the monosialogangliosides predominated in liver tissues following administration of the carcinogen. Increased levels of specific monosialogangliosides were present in nodules, in liver of carcinogen-treated animals prior to the appearance of tumors, and in the liver tissues surrounding nodules and hepatomas. In single hepatomas, ganglioside patterns correlated with tumorigenicity. A well-differentiated hepatoma had a normal complement of most gangliosides but was deficient in trisialogangliosides. In a poorly diferentiated but well-circumscribed hepatoma, the relative levels of all higher gangliosides were reduced. The monosialoganglioside Gal-GalNAc-(NAN)-Gal-Glc-Cer (GM1) accounted for 80% of the total ganglioside in a poorly circumscribed and poorly differentiated hepatoma. The ganglioside pattern of fetal livers most closely resembled that of a poorly differentiated hepatoma. During the first week post natum, levels of all higher monosialogangliosides and disialogangliosides declined, but the decline was most pronounced for gangliosides GM1 and GD1a. The ratio of GM1 + GD1a to GD1b + NAN-Gal-GalNAc-(NAN)2-Gal-Glc-Cer or (NAN)3-Gal-Glc-Cer (GT), used as an index of the relative predominance of the monoslaloganglioside and disialoganglioside pathways, fell from 2.7 for fetal liver to 0.4 for adult liver. Pools of precursor gangliosides increased during development, transiently for GalNAc-(NAN)-Gal-Glc-Cer and for more than 3 weeks for NAN-Gal-Glc-Cer. When hyperplastic nodules and hepatocellular carcinomas were compared, a reverse pattern was observed. The ratio of GM1 + GD1a to GD1b + GT rose steadily to values of 2.7 and 11...

Enzymatic synthesis of trisialoganglioside by particulate fractions of rat liver

Rat liver contains a particulate (membrane-bound) glycosyl transferase, concentrated in Golgi apparatus fractions, which catalyzes the synthesis of a trisialoganglioside from the ganglioside precursor disialohematoside (GD3). Sialic acid was not incorporated into exogenous GD1a from CMP-N-acetylneuraminic acid suggesting that GD1a is an endproduct of the monosialoganglioside pathway. Thus, the disialoganglioside pathway may be a primary source of trisialoganglioside and higher ganglioside homologs in adult rat liver.

Polyribosomes associated with forming acrosome membranes in guinea pig spermatids

Ribosomes, some of which are arranged in polyribosomal configurations, are attached to specialized regions of the acrosomal membrane in guinea pig spermatids. This finding indicates a new functional dimension for the acrosomal membrane, that of protein synthesis, and suggests that during acrosome formation, proteins of the acrosomal membrane or acrosomal contents need not be synthesized before or during passage through the Golgi apparatus.

Glycolipids as indicators of tumorigenesis

Hyperplastic liver nodules and hepatocellular carcinomas were induced in rats by oral administration of the carcinogen N-2-fluorenylacetamide. Neoplastic tissue was compared with control, fetal, neonatal, and precancerous liver tissues. The development of the tumors was slow, such that temporal changes in the biochemical and morphologic development of carcinogenesis could be identified. Ganglioside sialic acid levels were elevated in all but the most poorly differentiated tumors. Experiments to monitor individual enzymes suggested that the alterations in glycolipid composition were a direct effect of alterations in biosynthetic activities. The pattern during tumorigenesis was the inverse of that during normal development. Also, ganglioside patterns showed a progressive simplification from hyperplastic nodules to well-differentiated hepatomas and through two grades of poorly differentiated hepatomas. An increase in the activity of the branchpoint enzyme of ganglioside biosynthesis preceded both a decrease in the branchpoint enzyme of the disialoganglioside pathway and a marked increase in the galactosyltranferase of GM1 formation. The results indicate that ganglioside deletions are the end result of a cascade of events in the tumorigenic transformation. The onset of ganglioside deletions but not of the cascade per se may correlate with the onset of malignancy. Glycolipid levels are elevated early in certain surrounding tissues especially in the blood. In rats bearing transplantable hepatomas, serum levels of lipid-bound sialic acid were elevated 2.5-fold. Similar results were obtained with sera of mice bearing transplantable mammary carcinomas and of cancer patients. These findings provide new emphasis for gangliosides in both cancer detection and as regulatory signals for growth and multiplication of cells.

Dictyosome-like structures with cylindrical intersaccular connections (microtubules?) in guinea pig spermatocytes

Structures superficially resembling dictyosomes were present in guinea pig primary spermatocytes and in spermatids in late stages of development. The dictyosome-like structures (DLS) were composed of 2 to 17 saccules. Each saccule averaged about 20 nm in thickness (membranes plus lumen) and 400 nm in diameter and was separated from adjacent saccules in a stack by an intersaccular space of about 12 nm. Single saccules separated from the DLS were also present. Tubules up to 60 nm in diameter were continuous with the edges of the saccules and sometimes extended for several micrometers into the cytoplasm. The membranes of the tubules appeared similar to the saccule membranes. Some DLS saccules and tubules had coated vesicles attached to them. A distinguished feature of DLS was the presence of microtubule-like structures, about 10 nm in diameter, that bridged the inter-saccular spaces. Some of these bridging structures appeared continuous through one or more saccules. The bridging structures were often arranged in linear arrays or in clusters of three to four. The membranes of the DLS appeared tripartite but stained differently from the membranes of the endoplasmic reticulum or Golgi apparatus. The inner (luminal) leaflet of the tripartite membrane usually appeared discontinuous or globular after fixation in glutaraldehyde-osmium tetroxide. The DLS could be distinguished from all other cellular components and may represent a new organelle unique to spermatogenesis.

Glycolipid-bound sialic acid in serum: increased levels in mice and humans bearing mammary carcinomas

In mice bearing transplantable mammary carcinomas, serum levels of sialic acid-containing glycolipids were elevated 2.5-fold in pooled serum samples from which gangliosides were purified by column chromatography. A method is also described by which ganglioside content was estimated on as little as 1.0 ml of whole blood to permit studies with individual tumor-bearing mice and age- and litter-matched controls. Using this method, we observed similar elevations in ganglioside levels that were independent of age and sex of the animal and appeared in advance of palpable tumors. Following excision of the tumors, the glycolipid sialic acid values dropped below control levels and remained there. Serum sialic acid of the glycolipid fraction was elevated nearly 2-fold in human carcinoma patients and appeared to decline after surgery.

Evidence for an increase in microviscosity of plasma membranes from soybean hypocotyls induced by the plant hormone, indole-3-acetic Acid

The plant hormone indole-3-acetic acid (IAA or auxin) added at a concentration for half-maximal promotion of cell elongation (1 mum) caused an increase of 25% in the fluorescence polarization of the membrane-bound probe N-phenyl-1-naphthylamine, when added to fractions enriched in plasma membranes from soybean hypocotyls (Glycine max L. var. Wayne), with no measurable change in fluorescence lifetime. The amplitude of the polarization increase was maximal in the temperature range 12 to 22 C. The findings provide evidence for a cell-free response of isolated plasma membranes to the hormone and imply that the response involves an increase in the microviscosity of hydrocarbon regions of the membrane.

Ultrastructural alteration of plant plasma membranes induced by auxin and calcium ions

Ultrastructural changes in isolated and in situ plasma membranes of etiolated soybean hypocotyls (Glycine max L. cv. Wayne) were induced by indole-3-acetic acid (IAA), other auxins, and calcium chloride. Fixed and embedded preparations were stained by a phosphotungstate-chromate procedure to identify and accentuate plasma membrane. Measurements were on micrographs obtained with an electron optical system calibrated and corrected for reproducible and accurate size measurements. Plasma membranes treated for 20 minutes with 1 mum IAA were 10 to 15% thinner than controls. The response to IAA was rapid, reproducible, auxin-specific, temperature-dependent, and reversible. Comparable responses were obtained with isolated and in situ membranes. Membranes treated with 0.5 m calcium chloride for 20 minutes were 15 to 20% thicker than controls. Multiple cycles of alternating calcium and IAA treatments yielded membranes with dimensions that reflected the last treatment of the series. The findings show a direct response of plasma membranes to growth regulating agents and provide evidence for a cell-free response of isolated plasma membranes to a hormone.

Synthesis in vitro of intrinsic membrane proteins by free, membrane-bound, and Golgi apparatus-associated polyribosomes from rat liver

A fraction of intrinsic membrane proteins was prepared from the major membranous cell components of rat liver by extraction of the membranes with KCl and deoxycholate. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the compositions of the intrinsic protein fractions from rough and endoplasmic reticulum, smooth endoplasmic reticulum. Golgi apparatus, plasma membrane, and nuclear envelope were similar to each other but distinct from that of mitochondria. Among endomembranes, differences were in the ratios of protein constituents plus a few protein bands of Golgi apparatus and plasma membranes not found in endoplasmic reticulum or nuclear envelope. The abilities of total rough endoplasmic reticulum, polysomes released from rough endoplasmic reticulum, and free polysomes to incorporate amino acids into the intrinsic protein fraction were tested in vitro. Polysomes bound to endoplasmic reticulum has the greatest capacity to synthesize proteins of this fraction as shown by co-purification of radioactive products and by immunoprecipitation. Although the majority of the radioactive products synthesized by bound polysomes were distinct from those synthesized by free polysomes, certain radioactive products synthesized by free polysomes also co-purified with intrinsic membrane proteins. The results show no absolute segregation between free and bound polysomes in the synthesis of intrinsic membrane proteins. However, the majority of these proteins appear to be synthesized by polysomes bound to the endoplasmic reticulum. Several intrinsic proteins found in plasma membranes do not appear in rough endoplasmic reticulum. To determine where these proteins were synthesized, the ability of other endomembrane components to support in vitro incorporation of [14C]leucine into protein was examined. In contrast to plasma membranes, isolated Golgi apparatus fractions did incorporate [14C]leucine to an extent greater than could be explained by contamination with rough endoplasmic reticulum. Golgi apparatus in situ and isolated from rat liver have polyribosomes associated with a zone of cytoplasm at the Golgi apparatus periphery occupied by tubules and vesicles. The polysomes are not directly attached to membranes as with rough endoplasmic reticulum and may represent a special class of "Golgi apparatus-associated" polysomes. The polysomes, when associated with Golgi apparatus membranes, incorporated amino acids in vitro. The products synthesized in vitro were analyzed by treatment with KCl and deoxycholate and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Certain proteins synthesized by the Golgi apparatus-associated polysomes remained insoluble after the treatment with KCl and deoxycholate. The proteins synthesized by the Golgi apparatus fraction had mobilities similar to proteins in plasma membranes which were absent from endoplasmic reticulum, and which were relatively minor components of Golgi apparatus...

Inhibition of 5'-nucleotidase by concanavalin A: evidence for localization on the outer surface of the plasma membrane

5'-Nucleotidase activity of rat liver plasma membrane is markedly inhibited by concanavalin A. Taken together with a unilateral pattern of labelling of concanavalin A binding sites with hemocyanin, the results indicate that an allosteric site of the enzyme is at the outer surface of the membrane.

Ganglioside biosynthesis. Characterization of uridine diphosphate galactose: GM2 galactosyltransferase in golgi apparatus from rat liver

An enzyme that transfers galactose from UDP-Gal to ganglioside GM2 (Tay-Sachs ganglioside) was concentrated 50 times in Golgi apparatus from rat liver relative to total homogenates. This enzyme required detergents or phospholipids as dispersing agents. Of the numerous detergents tested, sodium taurocholate and Triton CF-54 were most effective in stimulating the reaction. Cardiolipin alone was more effective than any of the detergents tested in stimulating enzyme activity. The pH optimum for the reaction varied with the nature of the dispersing agent. With sodium taurocholate, Triton CF-54 and cardiolipin, the pH optima were 6.2, 5.9, and 5.6, respectively. The enzyme had a nearly absolute requirement for Mn2+, with maximum activity being attained at a concentration of 15 mM Mn2+. Other divalent or trivalent cations were either less effective than Mn2+ or inhibited the transferase reaction. The Km values calculated for UDP-Gal and GM2 were 1.1 X 10(-4) M and 9.9 X 10(-5) M, respectively. The enzyme could not be dissociated from Golgi apparatus fractions by treatment with ultrasound, indicating that it is tightly associated with the membrane and not part of the luminal contents. The newly synthesized GM2, the product of the reaction, was incorporated into or became tightly associated with the membranes of the Golgi apparatus.

Association of Phytochrome with Rough-surfaced Endoplasmic Reticulum Fractions from Soybean Hypocotyls

Distribution of phytochrome (as Pfr) among membranes from soybean hypocotyls (Glycine max L. cv. Wayne) was determined by the combined techniques of cell fractionation, difference spectrometry, and electron microscopic morphometry. More than 90% of the phytochrome was found in the soluble fraction. With homogenates prepared in the presence or absence of Mg(2+), the portion associated with membrane was only 6.5% and 1%, respectively. In the presence of Mg(2+), the content of particulate phytochrome correlated with the amount of endoplasmic reticulum with attached ribosomes in the fractions but not with mitochondria or other membranes (including endoplasmic reticulum membranes from which the ribosomes may have been lost during cell fractionation). In the absence of Mg(2+), phytochrome was associated with a "heavy" plasma membrane fraction. The phytochrome content was sufficiently low to be accounted for by a contamination of less than 10% by rough-surfaced fragments of endoplasmic reticulum. The findings show association of phytochrome with a particulate fraction enriched in rough-surfaced fragments of endoplasmic reticulum but do not rule out cosedimentation of some unknown or unspecific phytochrome aggregate with this fraction.