Glycoproteins of the chromaffin granule membrane: separation by two-dimensional electrophoresis and identification by lectin binding

Chromogranin A from bovine adrenal medulla: molecular characterization of glycosylations, phosphorylations, and sequence heterogeneities by mass spectrometry

Chromogranin A (CGA) is a member of a family of acidic glycoproteins present in endocrine and neuroendocrine tissues. One of its suggested physiological roles is being a precursor molecule for several peptide hormons. Further interest in this protein has recently originated from its potential role in pathophysiological processes of Alzheimer's disease. The concentration of CGA in the brain has been used for diagnosis of this disease, and CGA as an insoluble deposit has been found in the extracellular beta-amyloid plaques. By developing a new purification procedure we were able to isolate abundant CGA in high purity from bovine chromaffin cells. A MALDI-MS analysis of the intact protein revealed a heterogeneous molecular mass of ca. 50 kDa, indicating several structure modifications. By use of several subsequent proteolytic/chemical cleavage steps, HPLC isolation, a newly developed deglycosylation procedure, and several MS and MS-MS fragmentation approaches, the complete primary structure of CGA including four sequence heterogeneities, two O-glycosylations, five phosphorylations, and one disulfide bridge could be characterized. For both glycans six different forms could be identified. Ser167 was found to be mainly glycosylated by a trisaccharide, and Thr231 was found to be mainly glycosylated by a tetrasaccharide. Ser81, Ser124, and Ser297 residues were partially phosphorylated, whereas Ser372 and Ser377 were found completely phosphorylated. Sequence heterogeneities were identified in positions 293 (H/R), 301 (K/E), and 373 (Q/R) and at the partly missing C-terminal residue. Furthermore, a disulfide bridge between Cys17 and Cys38 was ascertained.

Membrane composition of adrenergic large and small dense cored vesicles and of synaptic vesicles: consequences for their biogenesis

The membrane proteins of adrenergic large dense cored vesicles, in particular those of chromaffin granules, have been characterized in detail. With the exception of the nucleotide carrier all major peptides have been cloned. There has been a controversy whether these vesicles contain antigens like synaptophysin, synaptotagmin and VAMP or synaptobrevin found in high concentration in synaptic vesicles. One can now conclude that large dense core vesicles also contain these peptides although in lower concentrations. The biosynthesis of large dense core vesicles is analogous to that of other peptide secreting vesicles of the regulated pathway. One cannot yet definitely define the biosynthesis of small dense core vesicles which apparently have a very similar membrane composition to that of large dense core vesicles. They may form directly from large dense core vesicles when their membranes have been retrieved after exocytosis. These membranes may become sorted in an endosomal compartment where peptides may be deleted or added. Such an addition could be derived from synaptophysin-rich vesicles present in adrenergic axons. However small dense core vesicle peptides may also be transported axonally independent of large dense core vesicles. For proving one of these possibilities some crucial experiments have been suggested.

Chromaffin granule membrane glycoprotein IV is identical with Ac45, a membrane-integral subunit of the granule's H(+)-ATPase

Glycoprotein IV of bovine adrenal chromaffin granule membranes was purified by membrane fractionation with Triton X-114 and lectin affinity chromatography. An antiserum raised against this protein recognized the same component as one directed against subunit Ac45 of the proton-translocating adenosine triphosphatase in the granule membrane. Amino acid sequencing confirmed that glycoprotein IV and Ac45 are identical proteins, and also showed that they are derived from a larger precursor by removal of a 246-amino acid N-terminal sequence. Enzymatic deglycosylation indicated an apparent polypeptide molecular mass of 29 kDa for the mature Ac45/glycoprotein IV. Blue Native electrophoresis confirmed that this protein is a component of the membrane sector of the V-ATPase.

Glycoprotein III (clusterin, sulfated glycoprotein 2) in endocrine, nervous, and other tissues: immunochemical characterization, subcellular localization, and regulation of biosynthesis

Specific antisera were raised against the A and B chains of glycoprotein III. Immunoblotting revealed that in adrenal medulla both chains migrate very closely together in two-dimensional electrophoresis. Both chains with slightly differing molecular sizes are found in several endocrine tissues and in brain, kidney, liver, and serum. The mRNA has an analogous widespread distribution. In primary cultures of chromaffin cells the level of message becomes significantly increased by treatment with histamine or 12-O-tetradecanoylphorbol 13-acetate/forskolin. However, the increase is small when compared with that of secretogranin II. The subcellular localization of glycoprotein III in endocrine organs and in the posterior pituitary was investigated by subcellular fractionation and immunoelectron microscopy. Glycoprotein III was found to be confined to the large dense-core vesicles of these organs. For a discussion of the function of glycoprotein III, its localization in these organelles has to be taken into account.

The interaction of tetanus toxin with intact bovine adrenal chromaffin cells: binding of toxin and subsequent inhibition of catecholamine release

Tetanus toxin (about 1 nM) inhibits 70% of the nicotine-evoked release of catecholamines from intact adrenal medullary chromaffin cells after 20 h of incubation and 30% of the K(+)-evoked release. Inhibition of Ca(2+)-evoked release from detergent-permeabilized cells requires higher concentrations of toxin (about 1 microM) toxin, but is maximal after 12 min. Preincubation of the intact cells with ganglioside GT1 in the absence of toxin also inhibits evoked secretion. 125I-labelled toxin bound specifically to these cells; the binding capacity was greater at pH 6 (about 1 pmol toxin/mg cell protein) than at pH 7.4 (about 0.25 pmol). In both cases there were at least two binding components: one of high affinity (Kd about 1 nM) accounting for about 20% of total binding and one of lower affinity (Kd 10-20 nM). Preincubation of the cells with ganglioside increased the binding capacity, but did not affect the Kd of the lower affinity component. Similar observations could be made when binding was measured immunocytochemically. Extraction of gangliosides from chromaffin cells and overlay experiments with radiolabelled toxin showed that, as well as GM3, the major ganglioside component of chromaffin cell membranes, a ganglioside having the chromatographic mobility of GT1 was a major ligand for toxin.

Developmental and strain-specific heterogeneity of rat adrenal chromaffin cells recognized by a monoclonal antibody against intact chromogranin B

We have raised a monoclonal antibody (MAB-1E10) reactive with the intact forms but not the processing products of the chromaffin cell vesicle protein chromogranin B (CgB). The antibody recognizes rat and human, but not bovine and chick adrenal chromaffin cells. In addition, MAB-1E10 immunoreactivity was detected in rat PC 12 pheochromocytoma cells and in pituitaries. Several other tissues, including pancreas, small intestine and superior cervical ganglia, which are known to contain CgB in endocrine cells or neurons, respectively, were found not to be reactive with MAB-1E10. Using short-term cultures of dissociated adrenal chromaffin cells from Hannover-Wistar rats, we found that the expression of intact CgB is developmentally regulated. Between embryonic day 19 and postnatal day 40, about 80% of adrenal chromaffin cells--identified by their reactivity with an antibody against the enzyme dopamine-beta-hydroxylase--were found to be reactive with MAB-1E10. The proportion of positive cells subsequently decreased to about 5% at postnatal day 90. In the presence of glucocorticoids, this decrease was reduced to about 45% CgB-positive cells at postnatal day 90. In another rat strain, Sprague-Dawley rats, the proportion of MAB-1E10-immunoreactive chromaffin cells (about 50%) remained constant from birth to adulthood. Our results indicate that CgB is differentially expressed and/or processed in different rat tissues, strains and during development, and furthermore, that expression or processing in rat chromaffin cells might be regulated by glucocorticoids. Intact CgB appears to be a marker for a subpopulation of chromaffin cells, but its function(s) remains to be clarified.

Characterization and purification of the monoamine transporter of bovine chromaffin granules

The monoamine transporter of the chromaffin granule membranes can be specifically labeled by the photoaffinity reagent 7-azido-8-[125I]iodoketanserin. The characteristics of the labeled protein have been investigated. Two-dimensional gel electrophoresis of the labeled membranes indicated a MW of about 70,000 and an isoelectric point ranging from 3.8 to 4.6. No clear protein spot was associated with the radioactive material, which migrated between glycoproteins GPII and GPIV. The diffuse aspect of the radioactive material indicated a heterogeneity, which was not modified after a second electrophoresis. This heterogeneity was, at least partially, due to glycosylation of the transporter; neuraminidase treatment increased the protein pI up to 6.3, whereas digestion with N-glycopeptidase markedly decreased the apparent MW, from 70,000 to 50,000. SDS-polyacrylamide gel electrophoresis showed that, at low acrylamide concentrations, the labeled material migrated more rapidly than predicted from the mobility of the markers of molecular weight, a behavior which indicated a marked hydrophobicity of the transporter. The labeled protein was purified to homogeneity by a combination of chromatography on DEAE-cellulose at pH 4.5, on immobilized wheat germ agglutinin, and on hydroxylapatite in the presence of SDS. During this purification, the specific radioactivity was increased by a factor of 300-500, with a yield of 10-20%.

Immunological characterization of the endoproteases PC1 and PC2 in adrenal chromaffin granules and in the pituitary gland

Specific antisera against synthetic fragment of the endoproteases, PC1 and PC2, were used to characterize these proteins. In one-dimensional immunoblots these antisera labelled components of 85 kDa for PC1 and of 70 kDa for PC2 in purified bovine chromaffin granules and anterior and posterior pituitary of ox and rat. In membranes of bovine chromaffin granules glycoprotein H was identified as the major PC2 immunoreactive spot. A major part of these endoproteases appeared membrane bound.

Glycosylation and transmembrane topography of bovine chromaffin granule p65

The bovine homologue of p65, a calmodulin-binding protein located in the membranes of synaptic vesicles and endocrine secretory granules, has been studied by the use of monoclonal antibodies directed against this antigen and against dopamine beta-mono-oxygenase. The protein (apparent molecular mass 67 kDa; pI = 5.5-6.2) is partially degraded by treatment with neuraminidase or endoglycosidase F. Trypsin treatment of intact adrenal chromaffin granules or of granule membranes releases a soluble 39 kDa fragment of p65 which corresponds to the whole of its cytoplasmic domain. This domain contains both the epitope for the monoclonal antibody cgm67 and the calmodulin-binding site. The 20 amino acids at the N-terminus of this fragment are identical to part of the rat p65 sequence.

Amphiphilic and nonamphiphilic forms of bovine and human dopamine beta-hydroxylase

We show that human and bovine dopamine beta-hydroxylases (DBH) exist under three main molecular forms: a soluble nonamphiphilic form and two amphiphilic forms. Sedimentation in sucrose gradients and electrophoresis under nondenaturing conditions, by comparison with acetylcholinesterase (AChE), suggest that the three forms are tetramers of the DBH catalytic subunit and bind either no detergent, one detergent micelle, or two detergent micelles. By analogy with the Gna4 and Ga4 AChE forms, we propose to call the nonamphiphilic tetramer Dna4 and the amphiphilic tetramers Da4I and Da4II. In addition to the major tetrameric forms, DBH dimers occur as very minor species, both amphiphilic and nonamphiphilic. Reduction under nondenaturing conditions leads to a partial dissociation of tetramers into dimers, retaining their amphiphilic character. This suggests that the hydrophobic domain is not linked to the subunits through disulfide bonds. The two amphiphilic tetramers are insensitive to phosphatidylinositol phospholipase C, but may be converted into soluble DBH by proteolysis in a stepwise manner; Da4II----Da4I----Dna4. Incubation of soluble DBH with various phospholipids did not produce any amphiphilic form. Several bands corresponding to the catalytic subunits of bovine DBH were observed in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but this multiplicity was not simply correlated with the amphiphilic character of the enzyme. In the case of human DBH, we observed two bands of 78 and 84 kDa. As previously reported by others, the presence of the heavy subunit characterizes the amphiphilic forms of the enzyme. We discuss the nature of the hydrophobic domain, which could be an uncleaved signal peptide, and the organization of the different amphiphilic and nonamphiphilic DBH forms. We present two models in which dimers may possess either one hydrophobic domain or two domains belonging to each subunit; in both cases, a single detergent micelle would be bound per dimer.

Glycoprotein II from adrenal chromaffin granules is also present in kidney lysosomes

Glycoprotein II (GP II) is a protein found in the membranes of chromaffin granules from adrenal medulla. Immunoblotting (one- and two-dimensional) revealed that this antigen is also present in liver and in kidney. Subcellular fractionation of the latter organ indicated that GP II was present in lysosomes. This was confirmed by immunoelectron microscopy. The antiserum against GP II immunolabelled the membranes of organelles which could be identified as lysosomes by the labelling of their contents with an antiserum against cathepsin D. Thus GP II is an antigen common to secretory vesicles and lysosomes.

Identification and characterization of glycoproteins after extraction of bovine chromaffin-granule membranes with lithium di-iodosalicylate. Purification of glycoprotein II from the soluble fraction

Chromaffin-granule membranes were separated into insoluble and soluble fractions after extraction with lithium di-iodosalicylate (LDIS). These fractions were characterized by one- and two-dimensional gel electrophoresis, and glycoproteins were detected after electroblotting with peroxidase-labelled concanavalin A and wheat-germ agglutinin (WGA). The LDIS-insoluble fraction contained components identified as glycoproteins III, H, J and K (carboxypeptidase H). Microsequence analysis indicated that component J is an N-terminally extended form of glycoprotein K. A major glycoprotein, GpII (Mr 80,000-100,000), present in the LDIS-soluble fraction was purified by affinity chromatography on WGA-Sepharose. This was characterized by one- and two-dimensional gel electrophoresis with Coomassie Blue staining, by amino acid analysis and automated N-terminal sequence analysis. Extraction of chromaffin-granule membranes with LDIS is a simple and rapid procedure that facilitates studies concerned with the structure and function of membrane glycoproteins from these and other secretory granules.

Synaptophysin and chromogranins/secretogranins--widespread constituents of distinct types of neuroendocrine vesicles and new tools in tumor diagnosis

Normal and neoplastic neuroendocrine (NE) cells have been identified for many years by morphological criteria only. With the advent of immunocytochemistry, antibodies against NE-specific polypeptides have been used to identify NE cells that had been missed by conventional techniques, thus improving the diagnosis of NE cells. In this review article we discuss (i) the biochemical, cell biological and molecular biological data obtained so far for two major types of NE markers, synaptophysin, which is characteristic of the small "transparent-looking" neurosecretory vesicles, and the chromogranins/secretogranins, which are widespread constituents of the larger "dense-cored" secretory granules; (ii) the immunohistochemical data obtained for these marker proteins in normal and neoplastic human NE cells and tissues; and (iii) future possible developments involving these as well as other proteins that are associated with these two distinct secretory organelles of NE cells and may serve as potential markers in NE cell diagnosis.

Biochemical and immunological characterization of the surface proteins of Borrelia burgdorferi

The immunodominant proteins and glycoproteins of Borrelia burgdorferi were analyzed by one-dimensional (1D) and 2D gel electrophoresis. More than 100 polypeptide species could be detected on silver-stained 2D gels. Separation of sonic extracts of the organism by differential centrifugation (100,000 X g) revealed several of the major proteins to reside predominantly within the pellet fraction. The antigenicity of the individual polypeptides was determined by Western (immuno-) blot analysis with sera from humans with chronic Lyme disease and from rabbits immunized with B. burgdorferi. Surface proteins of viable B. burgdorferi labeled with 125I or long-arm hydroxysuccinimide biotin were identified by gel analyses. Thirteen major surface proteins were apparent, including the highly immunogenic 41-kilodalton (kDa) endoflagellar antigen. Two of these proteins, with molecular masses of 22 and 41 kDa, were further characterized by electroblotting and microsequencing their amino termini. Significant (35%) homology between the first 20 amino acids of the 22-kDa protein and the deduced amino acid sequence of the 31-kDa (outer surface protein A) protein of B. burgdorferi may indicate that these proteins are processed similarly or are part of a gene family expressed at the surface of the organism. In addition, highly significant (88%) homology was found between the first nine amino acids of the 41-kDa protein of B. burgdorferi and the 33-kDa endoflagellar protein of Treponema pallidum, after which the sequences diverge. This observation provides in part a structural basis for the observed cross-reactivity between the two organisms and suggests alternative approaches to the development of specific immunodiagnostics.

Topography of a vacuolar-type H+-translocating ATPase: chromaffin-granule membrane ATPase I

Proteins exposed on the cytoplasmic face of isolated chromaffin granules were labelled by lactoperoxidase-catalysed radioiodination and by non-enzymic biotinylation. Granule membranes were then prepared, and the H+-translocating ATPase isolated by fractionation with Triton X-114. The labelling of individual ATPase subunits was assessed by polyacrylamide-gel electrophoresis, followed by autoradiography or by blotting and decoration with 125I-labelled streptavidin. Subunits of 72, 57 and kDa were strongly labelled, and could be removed from the membrane at pH 11: they are therefore extrinsic proteins. The 120 kDa subunit was also labelled, but it was not solubilized at pH 11. Photolabelling with a hydrophobic probe indicated that this subunit penetrates the bilayer, and enzymic degradation studies showed the presence of N-linked oligosaccharides; this subunit therefore spans the chromaffin-granule membrane. Labelling of the 17 kDa subunit occurred predominantly on the extracytoplasmic (matrix) face of the granule membrane. These results are consistent with this V-type ATPase having a structure that is generally similar to that of mitochondrial (F-type) ATPases, although the attachment of the 120 kDa subunit may be asymmetrical.

Poly(N-acetyllactosaminyl) oligosaccharides of chromaffin granule membrane glycoproteins

Poly(N-acetyllactosaminyl) oligosaccharides have been identified, on the basis of their susceptibility to endo-beta-galactosidase, in a large-molecular-size glycopeptide fraction derived from chromaffin granule membrane glycoproteins. The glycoproteins containing poly(N-acetyl-lactosaminyl) oligosaccharides were selectively labeled by treatment of chromaffin granule membranes with endo-beta-galactosidase to expose N-acetylglucosamine residues, followed by incubation with galactosyltransferase and UDP-[14C]galactose. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography demonstrated specific labeling in the 41-47 kilodalton (kD) region and in a distinct band at 90 kDa. Two-dimensional SDS-PAGE revealed that the poly(N-acetyllactosaminyl) oligosaccharides are predominantly present in glycoprotein IV, together with lesser labeling of glycoproteins II and III, whereas they are absent from dopamine beta-hydroxylase and carboxypeptidase H, which are the major glycoproteins of chromaffin granule membranes.

In adrenal medulla synaptophysin (protein p38) is present in chromaffin granules and in a special vesicle population

We have analyzed the properties and subcellular localization of synaptophysin (protein p38) in bovine adrenal medulla. In one-dimensional immunoblotting the adrenal antigen appears identical to synaptophysin of rat synaptic vesicles. In two-dimensional immunoblotting it migrates as a heterogeneous band varying in pI from 4.5 to 5.8. Subcellular fractionation by various sucrose gradients revealed that synaptophysin was present in two different cell particles. More than half of the antigens present in adrenal medulla were confined to special membranes that sedimented both with the "large granules" and with microsomal elements. These membranes could be removed from the large granule sediment by washing. In gradients it equilibrated in regions of low sucrose density. These membranes did not contain any markers for chromaffin granules. Less than half of the amount of synaptophysin present in adrenal medulla copurified with chromaffin granules. Despite several variations in the fractionation scheme synaptophysin could not be removed from chromaffin granules. After washing of granule membranes with alkaline solution synaptophysin still cosedimented in gradients with typical granule markers. The concentration of synaptophysin in membranes of chromaffin granules is low (less than 10%) when compared with synaptic vesicles. It is concluded that in adrenal medulla synaptophysin is present in special membranes, probably in high concentration, and in membranes of chromaffin granules, either in a low concentration in all or in a higher concentration in some of them.

Immunological characterization of a membrane glycoprotein of chromaffin granules: its presence in endocrine and exocrine tissues

A glycoprotein was isolated from detergent solubilized membranes of bovine chromaffin granules by high-performance liquid chromatography. Specific antisera raised against this glycoprotein reacted in one- and two-dimensional immunoblots with a heterogeneous component with a pI of 4.2-4.7 and Mr 100,000. The antiserum against bovine glycoprotein II cross-reacted with an analogous component in several species. The specific localization of glycoprotein II in chromaffin granules was established by density gradient centrifugation followed by immunoblotting. The antiserum, as shown by one- and two-dimensional immunoblotting, reacted with an analogous antigen in the posterior pituitary, in endocrine (anterior pituitary, parathyroid gland) and exocrine (parotid gland, pancreas) organs. In the pancreas the protein reacting with the antiserum was found in the membranes of zymogen granules. The results demonstrate for the first time that secretory vesicles of endocrine and exocrine tissues have at least one common antigen, i.e. the glycoprotein II. It seems likely that this protein is involved in a basic function common to all secretory vesicles.

Comparisons of proteins and glycoproteins in neuronal plasma membranes, axolemma, synaptic membranes, and oligodendroglial plasma membranes

Neuronal membranes are unique in that they consist of several functionally distinct segments: the perikaryal plasma membrane, the axolemma, the synaptic membrane, and the dendritic membrane. Methods are now available to isolate the first three types of membranes as well as to isolate oligodendroglial plasma membranes. The protein and glycoprotein compositions for each set of membranes were analyzed by silver staining after separation by SDS polyacrylamide gradient gel electrophoresis and by radiolabeled lectin binding to glycoproteins transferred to nitrocellulose. Analysis of the composition of each set of membranes reveals that they are all complex structures consisting of heterogeneous mixtures of proteins and glycoproteins, ranging in molecular weights from greater than 200,000 to 15,000. Each membrane fraction presents a unique pattern of staining and of lectin binding. As there were proteins and glycoproteins in common among the membranes, there were also differences. Synaptic membranes and axolemma appeared to have more proteins of higher molecular weight than the other membranes. Neuronal plasma membranes had a major concanavalin A binding glycoprotein at 79 kDa, which was not found in the other membranes. The three neuronal membrane fractions had a common wheat germ agglutinin binding glycoprotein at 82 kDa. The most interesting finding was the intense binding of neuronal plasma membrane glycoproteins to Ulex europaeus, suggesting high levels of fucose-containing glycoproteins.

Identification of two glycoproteins of chromaffin granules as the carboxypeptidase H

An antiserum against carboxypeptidase H, an enzyme involved in the biosynthesis of neuropeptides such as the enkephalins, was used to identify the enzyme proteins in bovine chromaffin granules. Two-dimensional immuno- and lectin-blots revealed that two closely migrating glycoproteins which have been previously named J and K represented the enzyme. The same protein doublet was present in the membrane preparation and the soluble lysate of bovine chromaffin granules; however, the membrane contained significantly more enzyme protein.

Proton-translocating adenosine triphosphatase of chromaffin-granule membranes. The active site is in the largest (70 kDa) subunit

The proton-translocating adenosine triphosphatase (ATPase) of bovine chromaffin granules contains up to five different polypeptides. Its activity is inhibited by N-ethylmaleimide, and ATP protects the enzyme from inhibition. After treatment of membranes with N-[2-3H]ethylmaleimide, only one polypeptide is strongly radiolabelled: this is the largest (70 kDa) subunit of the proton-translocating ATPase. This subunit therefore contains the ATP-hydrolysing site. Two-dimensional electrophoresis reveals heterogeneity in this polypeptide.

Fractionation of membrane proteins by temperature-induced phase separation in Triton X-114. Application to subcellular fractions of the adrenal medulla

After solubilization with the detergent Triton X-114, membrane proteins may be separated into three groups: if the membrane is sufficiently lipid-rich, one family of hydrophobic constituents separates spontaneously at low temperature; warming at 30 degrees C leads to separation of a detergent-rich phase and an aqueous phase. Using the chromaffin-granule membrane as a model, we found that many intrinsic membrane glycoproteins are found in the latter phase, probably maintained in solution by adherent detergent. They precipitate, however, when this is removed by dialysis, leaving in solution those truly hydrophilic proteins that were originally adhering to the membranes. We have used this method with mitochondria, and with Golgi- and rough-endoplasmic-reticulum-enriched microsomal fractions: it has proved to be a rapid and convenient method for effecting a partial separation of proteins from a variety of different membranes.

Isolation of ATPase I, the proton pump of chromaffin-granule membranes

Chromaffin-granule membranes contain two ATPases, which can be separated by (NH4)2SO4 fractionation after solubilization with detergents, or by phase segregation in Triton X-114. ATPase I (Mr 400000) is inhibited by trialkyltin, quercetin and alkylating agents, and hydrolyses both ATP and ITP. It contains up to five types of subunit, including a low-Mr hydrophobic polypeptide that reacts with dicyclohexylcarbodi-imide; these subunits are unrelated to those of mitochondrial F1F0-ATPase, as judged by size and reaction with antibodies. ATPase II (Mr 140000) is inhibited by vanadate, and is specific for ATP; it has not been extensively purified. Proton translocation by resealed chromaffin-granule 'ghosts', measured by uptake of methylamine or by quenching of the fluorescence of 9-amino-6-chloro-2-methoxyacridine, is supported by the hydrolysis of ATP or ITP, and inhibited by quercetin or alkylating agents, but not by vanadate. ATPase I must therefore be the proton translocator involved in the uptake of catecholamines and possibly of other components of the chromaffin-granule matrix, whereas ATPase II does not translocate protons.

Glycoproteins of the chromaffin-granule matrix: use of lectin blotting to distinguish several separate classes

The soluble proteins released by hypotonic lysis of highly purified bovine adrenal chromaffin granules were analysed by one- and two-dimensional electrophoresis, followed by transfer to nitrocellulose and decoration with lectins or specific antibodies. The effects of neuraminidase treatment, and of chemical deglycosylation by trifluoromethanesulphonic acid, were investigated. It was shown that lectins could be used to distinguish the two major series of chromogranins from each other, from dopamine beta-hydroxylase and from several minor, unidentified glycoprotein components of the lysate. Antibody decoration revealed a complex series of peptides containing enkephalin sequences, some of which changed their electrophoretic mobility on treatment with trifluoromethanesulphonic acid.