Detection of 23-27 kDa GTP-binding proteins in platelets and other cells.

Membrane proteins from rabbit and human platelets were separated by SDS/polyacrylamide-gel electrophoresis and the resolved polypeptides blotted on nitrocellulose. A family of GTP-binding proteins, termed Gn proteins, was detected by incubation of these blots with [alpha-32P]GTP in the presence of Mg2+. A major Gn protein with a molecular mass of 27 kDa (Gn27) and lesser amounts of 23, 24 and 25 kDa Gn proteins were observed in platelet membranes; much smaller amounts were in the platelet soluble fraction. Binding of [alpha-32P]GTP by platelet Gn proteins was blocked by GDP, GTP or guanosine 5'-[gamma-thio]triphosphate, but not by GMP or adenosine 5'-[beta gamma-imido]triphosphate. Rabbit and human red-cell membranes contained only Gn27. When rat tissues were analysed for Gn proteins, the largest amounts were found in brain, which contained two membrane-bound forms (Gn27 and Gn26) and a soluble form (Gn26).     

Immunodetection of ralA and ralB GTP-binding proteins in various rat tissues and platelets

Polyclonal antibodies were generated against a synthetic peptide corresponding to the C-terminal (amino acids 192-204) region of ralA and ralB GTP-binding proteins. The ralA and ralB antibodies recognized a 27 kDa protein in the human platelet particulate fraction. Incubation of ralA antibodies with ralB immunizing peptide and ralB antibodies with ralA immunizing peptide prior to Western blotting did not abolish the ability of antibodies to recognize the 27 kDa protein in human platelet particulate fraction. However, when antibodies were incubated with the respective immunizing peptide prior to Western blotting, the 27 kDa human platelet protein was no longer recognized by the antibodies. Incubation of nitrocellulose blots containing polypeptides separated using SDS-PAGE with [-³²P]GTP demonstrated the presence of GTP-binding proteins of molecular mass between 23-27 kDa in rat platelets and the various tissues tested. Analysis using subtype specific antibodies demonstrated that both ralA and ralB GTP-binding proteins were expressed in rat platelets and the various tissues tested. The protein recognized by the ralA and ralB antibodies in rat tissues and platelets had mobility on SDS-PAGE identical to that of the human platelet ral protein. Varying amounts of these proteins were detected in all the tissues tested except white muscle which contained very low level of ralB protein. The widespread distribution of ralA and ralB GTP-binding proteins suggests that they may participate in a common pathway in mammalian cells and tissues.     

Gn-proteins are distinct from ras p21 and other known low molecular mass GTP-binding proteins in the platelet

The 27 kDa platelet membrane protein (Gn27) that binds [alpha-32P]GTP on nitrocellulose blots of SDS-polyacrylamide gels [(1987) Biochem. J. 245, 617-620] was compared with other low molecular mass GTP-binding proteins. Platelet membranes also contained 21 kDa proteins that bound anti-ras p21 antibody and 22-23 kDa proteins that could be ADP-ribosylated by botulinum neurotoxin type D. These groups of proteins were resolved electrophoretically from each other and from Gn27. A low molecular mass GTP-binding protein from bovine brain [(1987) Biochem. J. 246, 431-439] was also resolved from Gn27. At the levels normally present in cell membranes, only Gn-proteins bound significant amounts of [32P]GTP after transfer of protein from SDS-polyacrylamide gels to nitrocellulose.     

GTP-binding proteins in human platelet membranes serving as the specific substrate of islet-activating protein, pertussis toxin

Two GTP-binding proteins serving as the specific substrate of islet-activating protein (IAP), pertussis toxin, were purified from human platelet membranes as heterotrimers with an alpha beta gamma-subunit structure. The alpha of the major IAP substrate had a molecular mass of 40 kDa and differed from that of Gi 1 or Go previously purified from brain membranes. The partial amino acid sequences of the 40 kDa alpha completely matched with the sequences which were deduced from the nucleotide sequences of the human Gi 2 alpha gene. On the other hand, the alpha of the minor IAP substrate purified from human platelets was about 41 kDa and cross-reacted with an antibody raised against alpha of brain Gi 1 (Gi 1 alpha). These results indicate that the major IAP substrate present in human platelet membranes is a product of the Gi 2 alpha gene.     

Presence of guanine nucleotide-binding proteins in a plant hypocotyl microsomal fraction

The presence of specific guanine nucleotide-binding proteins in a zucchini (Cucurbita pepo L.) hypocotyl microsomal fraction was investigated. Polypeptides were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and transferred to nitrocellulose. Incubation of nitrocellulose blots with [alpha-32P]GTP and [gamma-32P]GTP indicated the presence of four specific and distinct GTP-binding proteins with molecular masses of approx. 23.4 kDa, 24.8 kDa, 26.6 kDa and 28.5 kDa. Binding of [alpha-32P]GTP could be completely prevented by 30 microM GDP or 10 microM guanosine 5'[gamma-thio]triphosphate. This report presents evidence for the presence in a microsomal fraction from zucchini hypocotyls of Gn-proteins as defined by Bhullar and Haslam (1987) Biochem.J. 245, 617-620. The four plant proteins resemble animal Gn-proteins when molecular weights and GTP-binding specificities are considered.     

Human and mouse cementum proteins immunologically related to enamel proteins

SDS-polyacrylamide gel electrophoresis, immunoblot and amino acid composition analyses were applied to human and mouse acellular cementum proteins immunologically related to enamelins and amelogenins. In this analysis, anti-mouse amelogenin, anti-human enamelin and synthetic peptide (e.g., -LPPHPGHPGYIC-) antibodies were shown to cross-react with tooth crown-derived enamelin with a molecular mass of 72,000 Da (72 kDa), amelogenins (26 kDa), and also to four human cementum proteins (72, 58, 50 and 26 kDa) and two mouse cementum proteins (72 and 26 kDa). Each of the antibodies recognized tooth root-derived cementum polypeptides which share one or more epitopes with tooth crown-derived enamel proteins. The molecular mass and isoelectric points for crown-derived and root-derived enamel-related proteins were similar. Analysis of human and mouse cementum proteins revealed a characteristic amino acid composition enriched in glutamyl, serine, glycine, alanine, proline, valine and leucine residues; compared to the major enamel protein amelogenin, cementum proteins were low in proline, histidine and methionine. The human and mouse putative intermediate cementum proteins appear to represent a distinct class of enamel-related proteins. Moreover, these results support the hypothesis that epithelial root sheath epithelia express several cementum proteins immunologically related to canonical enamel proteins.     

Characterization of two murine monoclonal antibodies (P10, P12) directed against different determinants on human blood platelet thrombospondin

Thrombospondin, a 450-kDa glycoprotein composed of three disulphide linked chains, is located in human blood platelet alpha-granules and is released from platelets upon stimulation. This glycoprotein is thought to play a major role in platelet aggregation. The aim of this study was to characterize two monoclonal antibodies (P10 and P12) directed against human blood platelet thrombospondin. When the released material obtained after stimulation of platelets with thrombin in the presence of 2 mM calcium was immediately treated with EDTA, labelled with 125I and incubated with monoclonal antibodies P10 and P12, both immunoprecipitated a major labelled protein band with a molecular mass of 160 kDa and a weaker band at 146 kDa, as analysed on reduced dodecyl sulphate/polyacrylamide gels. The major band corresponds in molecular mass to the thrombospondin subunits. If, however, the released material was left in the presence of Ca2+ for 48 h, then the main band was at 130 kDa and in addition one minor protein band (75 kDa) was immunoprecipitated by P10 whereas P12 recognized two minor protein bands (75 and 60 kDa). When P10 and P12 were incubated with 125I-labelled platelet releasates treated for 48 h at 4 degrees C with 10mM EDTA, three major protein bands (160, 146 and 130 kDa) were immunoprecipitated in addition to the minor bands mentioned above. These results indicate that thrombospondin is probably degraded by the endogenous platelet calcium-dependent protease. Investigation of tryptic peptide fragments of thrombospondin isolated by fast protein liquid chromatography showed that 125I-labelled antibody P10 bound to 400-kDa and 120-kDa fragments whereas 125I-labelled P12 only recognized a 400-kDa fragment. Competition studies involving solid-phase antibody binding and double antibody sandwich assays showed that P10 and P12 were directed against different determinants of thrombospondin. Purified thrombospondin, isolated in the presence of calcium, either directly or after treatment with EDTA, haemagglutinated trypsinized, formaldehyde-fixed sheep erythrocytes identically. The haemagglutination activity of EDTA-treated thrombospondin was inhibited by P10 and enhanced by P12. On the other hand, P10 and P12, despite their binding to calcium-treated thrombospondin, had no effect on its haemagglutination activity. Monoclonal antibodies P10 and P12 could be useful tools to investigate the role of thrombospondin in platelet aggregation.     

Characterization of a guanine nucleotide dissociation stimulator for a ras-related GTPase.

ras-related GTPases participate in signaling for a variety of cellular processes. The GTPases cycle between a GTP-bound active state and a GDP-bound inactive state. This cycling is partially controlled by guanine nucleotide dissociation stimulators (GDS, also known as exchange factors). We report on the molecular cloning of cDNAs encoding a new mammalian GDS protein, using sequences derived from the yeast ras GDS proteins as probes. The encoded protein stimulates the dissociation of guanine nucleotides from the ras-related ralA and ralB GTPases at a rate at least 30-fold faster than the intrinsic nucleotide dissociation rate. This new GDS, ralGDS, is at least 20-fold more active on the ralA and ralB GTPases than on any other GTPase tested, including other members of the ras family (H-ras, N-ras, K-ras, R-ras, rap1a and rap2), members of the rho family (rhoA, rhoB and CDC42-Hs) and members of the rab family (rab3a and ypt1). While the ralGDS protein is phosphorylated on serine residues, we find no evidence that phosphorylation affects the activity of insect cell-expressed ralGDS towards the ralA or ralB GTPase. The 3600 nucleotide ralGDS mRNA and the 115 kDa protein were found in all tissues and cell lines examined.     

Compartmentalization of low molecular mass GTP-binding proteins among neutrophil secretory granules

Neutrophils contain several distinct classes of secretory granules that may sequentially fuse with the phagosome after the ingestion of particulates, or that may be differentially exocytosed after cellular activation with soluble stimuli. The exocytosis of neutrophil secretory granules has been shown to be GTP-dependent at a step distal to activation of the transductional G proteins. Inasmuch as ras-related low molecular mass GTP-binding proteins have been shown to play regulatory roles in vesicle sorting in the secretory pathway in yeast, the differential mobilization of neutrophil granules might be regulated by distinct GTP-binding proteins. We therefore explored the distribution and identity of low molecular mass GTP-binding proteins in neutrophil secretory granules and other subcellular fractions. After lysis by nitrogen cavitation, four highly resolved fractions were harvested from discontinuous Percoll gradients: a microsomal fraction enriched for plasma membranes, specific granules, primary granules, and cytosol. At least seven bands of distinct Mr were detected by probing protein blots with [32P]GTP. Microsomes contained a prominent GTP-binding band at 26 kDa and weaker ones at 24 and 22.5 kDa; specific granules contained bands at 26, 24, 22, and 20 kDa; primary granules showed bands at 24 and 23 kDa; cytosol showed strong bands at 23.5 and 19 kDa and a weak band at 26 kDa. Antiserum against ADP-ribosylation factor reacted strongly with the 19-kDa band in cytosol but with none of the membrane fractions. None of these proteins was recognized by antibodies against ras or against Sec4p. Botulinum exoenzyme C3 labeled bands of molecular mass 20 and 21 kDa in cytosol and microsomes that have distinct mobilities from all the blotted [32P]GTP-binding proteins. The highly compartmentalized subcellular distribution of the blotted [32P]GTP-binding proteins in neutrophils is consistent with a regulatory role in the differential mobilization of granule compartments during cellular activation.     

Identification and localization of low-molecular-mass GTP-binding proteins associated with synaptic vesicles and other membranes

GTP-binding proteins were studied in synaptic vesicles prepared from bovine brain by differential centrifugation and separated further from plasma membranes using gel permeation chromatography. Following separation by SDS-PAGE of proteins from the different fractions, and transfer to nitrocellulose sheets, the presence and localization of low-molecular-mass GTP-binding proteins were assessed by [alpha-32 P]GTP binding. The vesicle-membrane fraction (SV) was enriched in synaptophysin (p38, a synaptic vesicle marker) and contained low-molecular-mass GTP-binding proteins; these consisted of a major 27 kDa protein and minor components (Mr 26 and 24 kDa) which were trypsin-sensitive and immunologically distinguishable from ras p21 protein. GTP-binding proteins of low molecular mass, but displaying less sensitivity to trypsin, were also found in the plasma membrane fraction (PM; enriched in Na+/K(+)-ATPase). In addition, the PM fraction contained GTP-binding proteins with higher Mr (Gi alpha and G0 alpha), together with another GTP-binding protein, ras p21. Putative function(s) of these GTP-binding proteins with low mass are discussed.     

Two-dimensional polyacrylamide gel electrophoresis of bovine semen after cryopreservation in half-milliliter straws

One of the problems encountered with two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) is the streaking of proteins so that individual spot identification is compromised. This study was conducted to determine whether a low loading dose (50 microg) of protein would permit resolution of more discrete protein spots using megapixel camera technology, and if so, to present a nomenclature for future comparisons of the identified proteins. If the major proteins could be identified in a 50-microg sample we aimed to determine whether they could be identified in the supernatant (seminal plasma plus extender) of cryopreserved semen. Two ejaculates were obtained from each of 6 bulls and bovine seminal plasma (BSP) protein concentration was standardized to 50 microg/10 microl. Isoelectric points (pI) and molecular weights (MWt) of BSP proteins were determined by measuring spot mobility on 2-D PAGE (15% polyacrylamide). Three distinct protein spot constellations (a,b,c) could be readily seen by the naked eye and a faintly stained constellation "d" was identified by the megapixel camera. The image analysis software located 6 protein spots in both constellation "a" (MWt 26 kDa; pI 4.2 to 4.8) and "b" ( MWt 27 kDa; pI 6.6 to 8.0). Constellation "c" contained 13 protein spots distributed in a right-angled triangle with its base towards the acidic end of the gel (MWt 14.7 to 18.8 kDa; pI 5.3 to 7.4). Only spots c(2), c(3), c(5), c(8), and c(13) were present in all 12 samples. Streaking can be eliminated by using 50 microg protein for 2-D PAGE, and the major protein spots are readily identified by megapixel camera technology. Protein spots c(3), c(5), c(13) and constellation "a" appear to correspond with Manjunath's proteins (BSP-A(1), -A(2); -A(3); -30 kDa). Killian's 2 low fertility proteins may lie in the "c" constellation, and 1 of the high fertility proteins may lie in the "b" constellation. The 3 major BSP proteins can be visualized in the supernatant of cryopreserved semen. We believe that the technique may prove useful for retrospective analysis of processed semen batches that achieve less than satisfactory results in the field.     

Glycosylation of procathepsin L does not account for species molecular-mass differences and is not required for proteolytic activity.

Cathepsin L is a major lysosomal cysteine proteinase in mouse and human cells. Despite similar predicted molecular masses, procathepsin L in these two species migrates on SDS/polyacrylamide gels with apparent molecular masses of 39 kDa and 42 kDa respectively. To determine if glycosylation differences account for this discrepancy, and to ascertain whether glycosylation is essential for enzymic activity, mouse and human procathepsins L were expressed at high concentrations in mouse NIH 3T3 cells or in human A431 cells after DNA-mediated transfection of cloned DNAs for these enzymes. In pulse-chase studies, human procathepsin L transfectants synthesized and secreted large amounts of enzymically active 42 kDa proenzyme and processed it into 34 kDa and 26 kDa intracellular peptides, a pattern of secretion and processing similar to that seen with endogenous or transfected mouse procathepsin L. Both translation of cloned procathepsin L cDNAs in vitro and Endoglycosidase H treatment of 39 kDa mouse and 42 kDa human procathepsin L resulted in non-glycosylated proteins 2 kDa lower in molecular mass than the untreated proteins for both species. This suggests that glycosylation differences are not responsible for the molecular-mass disparity between the two species. Moreover, Endoglycosidase H-treated mouse enzyme retained full proteolytic activity, indicating that glycosylation of cathepsin L is not essential for enzymic function.     

Facilitated glucose transporter of human erythrocyte: proteolytic mapping of the [3H]cytochalasin B photoaffinity-labeled transporter polypeptide

The human erythrocyte D-glucose transporter is an integral membrane glycoprotein with an heterogeneous molecular mass spanning a range 45-70 kDa. The protein structure of the transporter was investigated by photoaffinity labeling with [3H]cytochalasin B and fractionating the labeled transporter according to molecular mass by preparative SDS-polyacrylamide gel electrophoresis. Each fraction was digested with either papain or S. aureus V8 proteinase, and the labeled proteolytically derived peptide fragments were compared by SDS polyacrylamide gel electrophoresis. Papain digestion yielded two major peptide fragments, of approx. molecular mass 39 +/- 2 and 22 +/- 2 kDa; treatment with V8 proteinase resulted in two fragments, with mass of 24 +/- 2 and 15 +/- 2. Proteolysis of each transporter fraction produced the same pattern of labeled peptide fragments, irrespective of the molecular mass of the original fractions. The binding characteristics of [3H]cytochalasin-B-labeled transporter to Ricinis communis agglutinin lectin was examined for each transporter molecular mass fraction. It was found that higher-molecular-mass fractions of intact transporter had a 2-fold greater affinity for the lectin than lower-molecular-mass fractions (i.e., 67 kDa greater than 45 kDa fraction). However, proteolytically derived labeled peptide fragments from each fraction had minimal affinity for the lectin. These results suggest that the labeled peptide fragments have been separated from the glycosylated regions of the parent transporter protein. The present findings indicate that, although transporter proteins have an apparently heterogeneous molecular mass, some regions of the protein share a common peptide. Furthermore, the glycosylated regions appear to be located some distance from the [3H]cytochalasin-B-labeled site(s).     

Phosphorylation and dephosphorylation of human platelet surface proteins by an ecto-protein kinase/phosphatase system.

We have characterized a novel ecto-protein kinase activity and a novel ecto-protein phosphatase activity on the membrane surface of human platelets. Washed intact platelets, when incubated with [gamma-32P]ATP in Tyrode's buffer, showed the phosphorylation of a membrane surface protein migrating with an apparent molecular mass of 42 kDa on 5-15% SDS polyacrylamide gradient gels. The 42 kDa protein could be further resolved on 15% SDS gels into two proteins of 39 kDa and 42 kDa. In this gel system, it was found that the 39 kDa protein became rapidly phosphorylated and dephosphorylated, whereas the 42 kDa protein was phosphorylated and dephosphorylated at a much slower rate. NaF inhibited the dephosphorylation of these proteins indicating the involvement of an ecto-protein phosphatase. The platelet membrane ecto-protein kinase responsible for the phosphorylation of both of these proteins was identified as a serine kinase and showed dependency on divalent cations Mg2+ or Mn2+ ions. Ca2+ ions potentiated the Mg(2+)-dependent ecto-protein kinase activity. The ecto-protein kinase rapidly phosphorylated histone and casein added exogenously to the extracellular medium of intact platelets. Following activation of platelets by alpha-thrombin, the incorporation of [32P]phosphate from exogenously added [gamma-32P]ATP by endogenous protein substrates was reduced by 90%, suggesting a role of the ecto-protein kinase system in the regulation of platelet function. The results presented here demonstrate that both protein kinase and protein phosphatase activities reside on the membrane surface of human platelets. These activities are capable of rapidly phosphorylating and dephosphorylating specific surface platelet membrane proteins which may play important roles in early events of platelet activation and secretion.     

Biosynthesis of bikunin (urinary trypsin inhibitor) in rat hepatocytes.

One of the major sulfated proteins secreted by rat hepatocytes contains a low-sulfated chondroitin sulfate chain and its apparent molecular mass upon sodium dodecyl sulfate/polyacrylamide gel electrophoresis shifts from 40 to 28 kDa upon chondroitinase ABC treatment (E. M. Sj?berg and E. Fries, 1990, Biochem. J. 272, 113-118). These properties suggest that this protein is the rat homologue of the major trypsin inhibitor of human urine which was recently named bikunin. In serum, bikunin occurs mainly as a subunit of the pre-alpha-inhibitor and the inter-alpha-inhibitor; in these proteins it is covalently linked to the other polypeptides through its chondroitin sulfate chain. Bikunin has been shown to be synthesized by liver cells as a 42-kDa precursor, in which it is linked to alpha 1-microglobulin by two basic amino acids. We have isolated bikunin from rat urine and prepared antibodies against it. In rat hepatocytes pulse-labeled with [35S]methionine, these antibodies precipitated a labeled protein of 42 kDa. Upon chase, three different labeled proteins were recognized by the antibodies in the medium: one protein of 40 kDa (free bikunin), one of 125 kDa (presumably pre-alpha-inhibitor), and one greater than 240 kDa (possibly a protein related to the inter-alpha-inhibitor). Pulse-chase experiments with [35S]sulfate showed that these proteins occurred intracellularly as precursors containing alpha 1-microglobulin. These results demonstrate that the completion of the chondroitin sulfate chain and its coupling to other polypeptide chains occur before the cleavage of the alpha 1-microglobulin/bikunin precursor.     

Effects of small heat shock proteins on the thermal denaturation and aggregation of F-actin

Effect of recombinant chicken small heat shock protein with molecular mass 24 kDa (Hsp24) and recombinant human small heat shock protein with molecular mass 27 kDa (Hsp27) on the heat-induced denaturation and aggregation of skeletal F-actin was analyzed by means of differential scanning calorimetry and light scattering. All small heat shock proteins did not affect thermal unfolding of F-actin measured by differential scanning calorimetry, but effectively prevented aggregation of thermally denatured actin. Small heat shock protein formed stable complexes with denatured (but not with intact) F-actin. The size of these highly soluble complexes was smaller than the size of intact F-actin filaments. It is supposed that protective effect of small heat shock proteins on the cytoskeleton is at least partly due to prevention of aggregation of denatured actin.     

Evidence that platelet and skeletal sarcoplasmic reticulum Ca2+-ATPase are structurally distinct

Proteolytic digestion and indirect immunostaining were used to compare the platelet and sarcoplasmic reticulum Ca2+-ATPase proteins. When the platelet and sarcoplasmic reticulum Ca2+-ATPase proteins were digested in the native state with trypsin, the platelet Ca2+-ATPase, which had an apparent undigested molecular mass of 103 kDa, yielded 78-kDa and 25-kDa fragments. Calcium transport activity depended on the integrity of the 103-kDa protein, while the digested protein had residual ATPase activity. Tryptic digestion of the sarcoplasmic reticulum pump protein, which also had an undigested molecular mass of 103 kDa, yielded products with apparent molecular masses of 55 kDa, 36 kDa, and 26 kDa. Distinct patterns were also observed when the platelet and sarcoplasmic reticulum calcium pump proteins were digested with chymotrypsin and Staphylococcus aureus protease in the presence of sodium dodecyl sulfate. Chymotrypsin digestion of the platelet protein resulted in the appearance of products with apparent molecular masses of 70 kDa, 39 kDa, and 31 kDa, while a similar digestion of the sarcoplasmic reticulum calcium pump protein yielded 54-kDa, 52.5-kDa, 46-kDa, 41-kDa, and 36-kDa fragments. Exposure of the sarcoplasmic reticulum and platelet Ca2+-ATPase proteins to S. aureus protease also yielded dissimilar fragmentation patterns. These results indicate that the Ca2+-ATPases from platelets and sarcoplasmic reticulum are distinct proteins.     

Identification of novel GTP-binding proteins in the human neutrophil

We describe here the existence of previously undescribed GTP-binding proteins within the human neutrophil. These proteins specifically bind guanine nucleotides under conditions in which the previously characterized G-proteins are unable to bind. We have partially purified these proteins and present both functional and immunologic data which indicate that they are unrelated to Gn, the major neutrophil pertussis toxin substrate. An additional protein, of apparent molecular mass 22 kDa, may be related to the ras G-protein family. Analysis of the structural and functional characteristics of these novel proteins will promote a better understanding of the process of neutrophil activation.     

Characterization of sucrose-hydrolyzing enzymes of Zymomonas mobilis

Extracellular proteins of Zymomonas mobilis were analyzed by two-dimensional gel electrophoresis and protein maps drawn up. One of these proteins showed sucrose-hydrolyzing activity, as indicated by activity staining after polyacrylamide gel electrophoresis. It was purified from the extracellular extract of a glucose fermentation by polyacrylamide gel electrophoresis, using a two-step procedure. The molecular mass of the protein was 46 kDa and its isoelectric point 5.0. A rabbit antiserum was raised against this protein. As shown by immunoblotting, the same protein was present in extracellular extracts obtained from glucose, fructose and sucrose fermentations. A cross-reaction was also detected by immunoblotting, with a cellular protein of molecular mass 46 kDa present on the three carbon sources studied. However, activity staining was unsuccessful on gels after electrophoresis of these cellular extracts. The extracellular protein extract obtained from a fermentation run on glucose contained another sucrose-hydrolyzing protein of molecular mass 51 kDa and with an isoelectric point of 4.8. This protein was absent in fructose and sucrose fermentations but showed a positive reaction with the antiserum raised against the 46 kDa extracellular protein. Partially purified sucrose-hydrolyzing proteins also catalyzed transfructosylation reactions, suggesting that they could be of the levansucrase type.     

Electrophoretic changes in olfactory system proteins in masu salmon during parr-smolt transformation

Changes in cytosolic proteins of the olfactory system (olfactory epithelium, olfactory nerve and olfactory bulb) and the telencephalon of masu salmon Oncorhynchus masou were analysed by two-dimensional polyacrylamide gel electrophoresis during parr-smolt transformation; parr, pre-smolt and full-smolt stages. In the olfactory system, several protein spots appeared and disappeared in the course of smolting. One protein spot in particular with an estimated molecular weight of 27 kDa and isoelectric point of 5.6 (M27) disappeared in common with the olfactory system during smolting. The disappearance of M27 was also observed in the telencephalon. These proteins, which appeared and disappeared, may reflect the changes in olfactory function during smolting. Simultaneously, the present study confirmed a salmonid olfactory specific protein of 24 kDa (N24), which existed in the olfactory system but not in the telencephalon, as a single neutral protein spot in masu salmon.