Subunit composition of vacuolar membrane H(+)-ATPase from mung bean

The vacuolar H(+)-ATPase from mung bean hypocotyls was solubilized from the membrane with lysophosphatidycholine and purified by QAE-Toyopearl column chromatography. The purified ATPase was active only in the presence of exogenous phospholipid and was inhibited by nitrate, dicyclohexyl carbodiimide and Triton X-100, but not by vanadate or azide. Dodecyl sulfate/polyacrylamide gel electrophoresis of the purified ATPase yielded ten polypeptides of molecular masses of 68 kDa, 57 kDa, 44 kDa, 43 kDa, 38 kDa, 37 kDa 32 kDa, 16 kDa, 13 kDa and 12 kDa. All polypeptides remained in the peak activity fraction after glycerol density gradient centrifugation. Nine of them, excluding the 43-kDa polypeptide, comigrated in a polyacrylamide gradient gel in the presence of 0.1% Triton X-100. The 16-kDa polypeptide could be labeled with [14C]dicyclohexylcarbodiimide. The amino-terminal amino acid sequence of the isolated 68-kDa polypeptide generally agreed with that deduced from the cDNA for the carrot 69-kDa subunit [Zimniak, L., Dittrich, P., Gogarten, J. P., Kibak, H. & Taiz, L. (1988) J. Biol. Chem. 263, 9102-9112]. Thus, mung bean vacuolar H(+)-ATPase seems to consist of nine distinct subunits.     

The Relationship Between the Activity of Cyanide-resistant Respiration and the Expression of Alternative Oxidase in Different Organs of Mung Bean Seedlings

Twelve peptides, including eight conservative amino acid residues in the amino acid sequence of hydrophilic S helix of the alternative oxidase (AOX), were synthesized by solid-phase method. The polypeptide was coupled to αchymotrypsinogen, and the antibodies against this complex were obtained in rabbit. By using these antibodies, which were raised to immunoreact with total proteins of purified mitochondria from different organs of mung bean (Phaseolous radiatus L.) seedlings, it was found that there were two hybridizable AOX fractions in the mitochondria of mung bean seedlings. Their molecular weight was about 35 kD and 38 kD, respectively. Moreover, among the respiratory parameters obtained in hypocotyl, true leaf and cotyledon of mung bean seedlings true leaf had the highest total respiration (Vt), alternative pathway (AP) capacity(Valt) and the activity of AP (ρValt). Hypocotyl Vt and ρValt were the lowest, but its Vt was higher than that of the cotyledon. The activities of total and cyanide-resistant respiration were consistant with the analysis of Western blotting of AOX expression. The highest Vt and ρValt in true leaf were accompanied by two hybridizable polypeptides of AOX protein. The next was cotyledon Vt and ρValt with only one 38 kD hybridizable polypeptide of AOX protein. Hypocotyl Vt and ρValt were the lowest and its immunobloting band was similar to that of the cotyledon, but the expression amount of 38 kD protein was less than that of the cotyledon. The 35 kD AOX may make the main contribution to the true leaf ρValt.     

Biosynthesis and intracellular processing of carbonic anhydrase in Chlamydomonas reinhardtii

Carbonic anhydrase (CA) of Chlamydomonas reinhardtii is a glycoprotein of 35 kDa which is localized outside the plasma membrane. The activity of CA was increased when the CO2 concentration during photoautotrophic growth was decreased to air level. After decreasing the CO2 concentration from 4% to 0.04%, several polypeptides including CA were induced continuously or transiently. To investigate the biosynthesis and intracellular processing of CA, the cells of wall-less mutant CW-15, which secretes CA into the culture medium, were pulse-labeled with radioactive arginine, chased, and radioactive proteins were immunoprecipitated with anti-CA serum. A 42-kDa polypeptide with isoelectric point (pI) of 7.1-7.3 was first synthesized. Within 5 min the molecular mass of this polypeptide was decreased to 35 kDa and it was then secreted into the culture medium within 30 min. This indicates that the former is the precursor form and the latter the mature form of CA. The primary translation product from poly(A)-rich RNA in a cell-free reticulocyte lysate system from a rabbit was a 38-kDa polypeptide. This was cotranslationally converted into the 42-kDa precursor in vitro in the presence of dog pancreatic microsomal membranes. As the 42-kDa precursor had a high affinity to concanavalin A, it was assumed to have a high-mannose-type oligosaccharide. The mature enzyme had a pI of 6.1-6.2 and was composed of more than two isoforms, which had a complex-type oligosaccharide with low affinity to concanavalin A. Chemical deglycosylation of the mature enzyme by trifluoromethanesulfonic acid indicated that the molecular mass of the polypeptide moiety was 32 kDa and the difference between this and the primary translation product suggests that cleavage of the polypeptide occurs during its biosynthesis.     

Pullulanase in mung bean cotyledons. Purification, some properties and developmental pattern during and following germination

Starch debranching enzyme was purified from mung bean ( Vigna radiata ) cotyledons to investigate its properties and developmental pattern during and following germination. A debranching enzyme was purified up to the step where only a doublet of polypeptides with molecular masses of 99 and 101 kDa, respectively, was detected by SDS-PAGE. The enzyme is thought to be a single chain monomer, as the molecular mass of the enzyme determined by gel filtration was 72 kDa. Monoclonal antibodies raised against the purified preparation recognized the doublet, indicating that the two polypeptides have immunological homology to each other. The enzyme preparation showed a high activity with pullulan as a substrate, low activity with soluble starch and amylopectin, and no activity with glycogen. These substrate specificities indicate that the debranching enzyme from mung bean cotyledons is of the pullulanase type. Immunoblotting profiles revealed that the enzyme is present in dry seeds and decreases gradually after imbibition, suggesting the possibility that the pullulanase plays a role in developing mung bean cotyledons.     

Biosynthesis of prostatic acid phosphatase in a normal human cell-line

The biosynthesis of the prostatic form of human acid phosphatase was studied in normal embryonic lung cells, WI-38, by metabolic labeling with tritiated leucine and [32P]phosphate, followed by specific immunoprecipitation, gel electrophoresis, and fluorography. Of the total tartrate-inhibitable acid phosphatase activity in WI-38 cells, 30% is due to the prostatic form. The primary translation product that leads eventually to the mature prostatic enzyme is a precursor polypeptide of 112 kDa. The precursor polypeptide is processed to mature polypeptides of 59, 55, and 49 kDa via an intermediate 91-kDa precursor. WI-38 cells also secrete a 113-kDa peptide into the medium. The precursor and mature polypeptides are glycosylated and phosphorylated. Upon treatment with endo-beta-hexosaminidase H, the apparent molecular weighs of the polypeptides are reduced by approximately 4 kDa and phosphate is lost.     

A 170 kDa polypeptide from mung bean shares multiple epitopes with rabbit skeletal myosin and binds ADP-adpagarose

A 170 kDa polypeptide that has been partially purified from mung beans is retained by ADPagarose even in the absence of divalent cations when most non-myosin ATPases and kinases do not bind. Attempts to demonstrate a myosin-like ATPase activity were inconclusive, however, and the protein accounts at most for only a small part of the total K⁺ EDTA ATPase activity of mung bean extracts. All four monoclonal antibodies raised to the 170 kDa polypeptide react with rabbit skeletal muscle myosin and localize the 170 kDa polypeptide in mung bean root tip cells to the actin-containing phragmoplast and to sites dispersed throughout the cytoplasm which probably include some but not all actin cables. These 4 monoclonals and 3 commercially available antimyosin monoclonals all recognise rabbit skeletal myosin and 160-170 kDa proteins that are present in two other angiosperms tested. In addition, a 158 kDa protein of mung bean reacts with only one antibody and does not bind ADP-agarose. We conclude that strong but not yet conclusive evidence points to the 160-170 kDa proteins of angiosperms being a widely conserved form of myosin heavy chain.     

Reconstitution of Tonoplast H+-ATPase from Mung Bean (Vigna radiata L.) Hypocotyls in Liposomes

Reconstituted proteoliposomes of tonoplast ATPase are formedon solubilization of tonoplast membranes from mung bean (Vignaradiata L.) with deoxycholate (DOC) in the presence of a mixtureof soybean phospholipids (asolectin), after removal of DOC bypassage through a PD-10 column (Pharmacia). This method is idealbecause of its simplicity and rapidity. Selective insertionof sets of tonoplast H⁺-ATPase polypeptides (68 kDa, 60 kDa,16 kDa and several minor polypeptides) into liposomes usingthis method was confirmed by SDS-PAGE and immuno-blotting withantibodies raised against 68-kDa and 60-kDa polypeptides. Pumping of protons across the membranes of the proteoliposomeswas demonstrated by quinacrine-fluorescence quenching in thepresence of ATP-Mg²⁺. ATP-Mg²⁺ was shown to be the preferredsubstrate in both reconstituted and native tonoplast vesicles,and its optimum concentration was 0.75 to 3.0 mM. Quenchingwas completely abolished by a channel-forming ionophore, gramicidinD, and an inhibitor of tonoplast H⁺-ATPase, KNO₃. Antibodiesto 68-kDa and 60-kDa peptides partially inhibited the pumpingof protons. The rate of pumping of protons increased with thenumber of proteoliposomes, the maximal concentration of whichwas equivalent to 250 µg of protein per reaction mixture.The optimum pH for pumping was 6.5 when inside of proteoliposomeswere loaded pH at 7.2. The rate of pumping of protons was reducedwhen proteoliposomes were made using asolectin and cholesterolat 3 : 1 (w/w), as compared with those made with asolectin alone. The ATPase activity in reconstituted proteoliposomes was inhibitedby KNO₃, with half-maximal inhibition at approximately 7 mM.The enzyme actively hydrolyzed ATP in preference to GTP, CTP,UTP, and ADP, but it did not hydrolyze pNPP or AMP. Antibodiesagainst the 60-kDa polypeptide strongly inhibited ATPase activityas compared to antibodies against the 68-kDa polypeptide. Theresults obtained in this study demonstrate directly that functionaltonoplast H⁺-ATPase can be inserted selectively into liposomes. (Received August 31, 1990; Accepted April 18, 1991)     

A vacuolar ATPase and pyrophosphatase in Acetabularia acetabulum.

Vacuole-rich fractions were isolated from Acetabularia acetabulum by Ficoll step gradient centrifugation. The tonoplast-rich vesicles showed ATP-dependent and pyrophosphate-dependent H(+)-transport activities. ATP-dependent H(+)-transport and ATPase activity were both inhibited by the addition of a specific inhibitor of vacuolar ATPase, bafilomycin B1. A 66 kDa polypeptide present in the preparation cross-reacted with the anti-IgG fractions against the alpha and beta subunits of Halobacterium halobium ATPase and with the antibody against the A subunit (68 kDa subunit) of mung bean vacuolar ATPase. A 56 kDa polypeptide present in the vacuole preparation showed cross-reactivity with the antibody against the B subunit (57 kDa) of mung bean vacuolar ATPase but not with the anti-beta subunit of H. halobium ATPase. A 73 kDa polypeptide cross-reacted with the antibody against inorganic pyrophosphatase of mung bean vacuoles. These results suggest that vacuolar membrane of A. acetabulum equipped energy transducing systems similar to those found in other plant vacuoles.     

Biosynthesis and processing of lysosomal acid phosphatase in cultured human cells

The biosynthesis of lysosomal acid phosphatase was studied in a normal human embryonic lung cell line, WI-38. Cells were labeled with radioactive leucine under a variety of conditions, the enzyme was immunoprecipitated using a monospecific antiserum raised against human liver lysosomal acid phosphatase, and the products were separated by electrophoresis and were visualized by fluorography. Lysosomal acid phosphatase constitutes 60% of the total tartrate-inhibitable acid phosphatase in WI-38. It is initially synthesized as a high-molecular-weight precursor polypeptide of 69 kDa. The precursor polypeptide is rapidly glycosylated and processed to a mature enzyme of 53-45 kDa via intermediates of 65 and 60 kDa in WI-38 cells. The 69-kDa precursor polypeptide is also converted to larger precursor polypeptides of 74 and 80 kDa. The multiplicity of precursor polypeptides is due at least in part to differences in the glycosylation and phosphorylation of the polypeptides. Sensitivity of phosphorylated oligosaccharide chains from precursor, mature and small polypeptides to endo-beta-hexosaminidase H-catalyzed cleavage suggests the presence of high-mannose phosphorylated oligosaccharide chains similar to those present on many other lysosomal enzymes. The effects of tunicamycin and ammonium chloride were also studied. In contrast to the effect of ammonium chloride on arylsulfatase A secretion, the lysosomal acid phosphatase in WI-38 cells was not secreted in the presence of NH4Cl. This is consistent with the existence of an alternate route for the transfer of lysosomal acid phosphatase into lysosomes. This alternate route may be the reason that I-cell fibroblasts contain a normal level of lysosomal acid phosphatase.     

Purification and characterization of two distinct complexes of assembly polypeptides from calf brain coated vesicles that differ in their polypeptide composition and kinase activities

The binding and assembly of clathrin triskelions on vesicle membranes seem to be mediated by certain assembly polypeptides (Keen, J.H., Willingham, M.C., and Pastau, I.H. (1979) Cell 16, 303-312). These assembly polypeptides were further purified into two distinct complexes using hydroxylapatite chromatography. Peak 1 consists of two major bands of 98 and 112 kDa, two minor bands of 103 and 118 kDa, and a polypeptide of 46 kDa. Peak 2 consists of one major band of 100 kDa, two minor bands of 103 and 115 kDa, and a polypeptide of 50 kDa. Both complexes have a native molecular mass of 290 kDa as determined by gel filtration. Each 290-kDa complex contains two polypeptides of 98-118/100-115 kDa and two polypeptides of 46/50 kDa. The 46-kDa polypeptide is not phosphorylated, whereas the 50-kDa polypeptide is. Both peaks contain 50-kDa kinase-like activity. Time courses of the 50-kDa phosphorylation show that the activity in peak 1 saturates much faster than the activity in peak 2; there may be two 50-kDa kinase activities in coated vesicles. A kinase that phosphorylates the polypeptides in 98-118-kDa group is present in peak 1 but not in peak 2. Both peaks assemble clathrin triskelions into cages under conditions in which the clathrin alone would not assemble. Both rotary shadowed and negatively stained preparations of these reassembled cages as well as the purified complexes were examined by electron microscopy. Thus, two complexes have been identified that differ in their polypeptide composition and kinase activities, but are similar in their ability to assemble clathrin triskelions into cages.     

Endo-β-mannanases in the endosperm of germinated tomato seeds

Three forms of galactomannan-hydrolyzing enzymes (dyed galactomannan as substrate) were partially purified from germinated tomato [ Lycopersicon esculentum (L.) Mill.] seed. Two of the enzymes were of the same molecular mass, 38 kDa, as judged by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), but the points of elution from a CM-Toyopearl column by a pH-gradient were different between the two (pH 5.15 and 5.45. respectively). The molecular mass of the third form was slightly less (37.5 kDa) than that of the other two. These 3 enzymes showed no α-galactosidase (EC 3.2.1.22) or β-mannosidase (EC 3.2.1.25) activity. Thin-layer chromatography (TLC) revealed that the products of the reaction were oligosaccharides and that free galactose and mannose were not released. These results indicate that the 3 galactomannan-hydrolyzing enzymes are endo-β-mannanases (EC 3.2.1.78). Polyclonal antibodies raised against the 37.5-kDa polypeptide cross-reacted with the two 38-kDa polypeptides, indicating that the 3 endo-β-mannanases are immunologically homologous. Activity staining and immunoblotting of native PAGE of endosperm extracts revealed that only two (38-kDa. elution point pH 5.15 and 37.5-kDa proteins) of the 3 forms were major endo-β-mannanases present in the endosperm of germinated tomato seeds.     

Characterization of Proteins of Nuclear Envelopes Prepared from Mung Bean Hypocotyls

The polypeptide composition of nuclear envelopes prepared fromhypocotyls of mung bean (Vigna radiata) was investigated. Thetissue was homogenized in the presence of Triton X-100 and nucleiwere isolated by differential and discontinuous Percoll gradientcentrifugation. The nuclei were subjected to sonication in 2M KC1 or 50 mM lithium diiodosalicylate and then the nuclearenvelopes were collected by centrifugation. Proteins in theenvelope fraction were analyzed by sodium dodecylsulfate-polyacrylamidegel electrophoresis and blotting techniques. When the envelopefraction was incubated with [-³²P]ATP, 10 to 15 polypeptideswere labeled and the intensity of labeling of some of thesepolypeptides was enhanced by the addition of calcium ions. Theresults suggest the presence of a protein-phosphorylation systemin nuclear envelopes. Three polypeptides of 100, 42, and 40kDa stained blue with the cationic carbocyanine dye "Stains-all",and they were labeled with ⁴⁵Ca²⁺ on a transfer membrane. Thelectin concanavalin A recognized glycoproteins that migratedas polypeptides of 50, 49, 47, 43, 35 and 32 kDa, respectively.Of these polypeptides the two larger ones were prominent andwere solubilized by treatment of the envelope fraction withKCl at 2 M but not at less than 100 mM. These results suggestthat the mung bean nuclear envelope contains some calcium-bindingproteins and glycoproteins. These newly identified proteinsmay become useful as characteristic markers of the nuclear envelope. (Received July 16, 1993; Accepted December 15, 1993)     

Tissue-Specific Isoforms of Catalase Subunits in Castor Bean Seedlings

Catalases purified from endosperm glyoxysomes and non-specializedmicrobodies from hypocotyls of castor bean seedlings differedin their specific activity [90–164 and 0.89–4.9kunits (mg protein)^–1, respectively] and in their constituentsubunits [two subunits of 54 and 56 kDa for the endosperm enzymeand only one of 56 kDa for the hypocotyl enzyme]. Immunoblotanalysis also showed that particulate fractions from the endospermsand from etiolated and green cotyledons contained two catalasesubunits of 54 and 56 kDa, whereas such fractions from the hypocotylsand roots contained only the 56-kDa subunit. Leaf peroxisomesfrom green leaves had two catalase subunits of around 55 kDaeach. Results of translation in vitro indicated that the 54-and 56-kDa subunits were translated from distinct mRNAs andlevels of both mRNAs increased in the endosperms during germination,prior to increases in levels of catalase proteins. In the hypocotyls,the 56-kDa subunit seemed to be synthesized constitutively. ¹Present addresses: YO, Toyota Central Institute, 31-9 Musashizuka,Nagabuchi, Nagakute, Aichi 480-11, Japan     

Purification and characterization of a cathepsin D protease from bovine chromaffin granules.

Purification and potential tachykinin and enkephalin precursor cleaving enzymes from bovine chromaffin granules was undertaken using as substrates the model precursors 35S-(Met)-beta-preprotachykinin [35S-(Met)-beta-PPT] and 35S-(Met)-preproenkephalin [35S-(Met)-PPE]. Purification by concanavalin A-Sepharose, Sephacryl S200, and chromatofocusing resulted in a chromaffin granule aspartyl protease (CGAP) that preferred the tachykinin over the enkephalin precursor. CGAP was composed of 47-, 30-, and 16.5-kDa polypeptides migrating as a single band in a nondenaturing electrophoretic gel system, and coeluting with an apparent molecular mass of 45-55 kDa by size-exclusion chromatography. These results suggest that two forms exist: a single 47-kDa polypeptide and a complex of 30 + 16.5-kDa-associated subunits. CGAP was optimally active at pH 5.0-5.5, indicating that it would be active within the acidic intragranular environment. Cleavage at basic residues was suggested by HPLC and HVE identification of 35S-(Met)-NKA-Gly-Lys as the major acid-soluble product generated from 35S-(Met)-beta-PPT. Neuropeptide K was cleaved at a Lys-Arg basic residue site, as determined by identification of proteolytic products by microsequencing and amino acid composition analyses. Structural studies showed that the three CGAP polypeptides were similar to bovine cathepsin D in NH2-terminal sequences and amino acid compositions, indicating that CGAP appears to be a cathepsin D-related protease or cathepsin D itself. The 47- and 16.5-kDa polypeptides of CGAP possessed identical NH2-terminal sequences, suggesting that the 16.5-kDa polypeptide may be derived from the 47-kDa form by proteolysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reconstitution of trimethylamine-dependent coenzyme M methylation with the trimethylamine corrinoid protein and the isozymes of methyltransferase II from Methanosarcina barkeri.

Reconstitution of trimethylamine-dependent coenzyme M (CoM) methylation was achieved with three purified polypeptides. Two of these polypeptides copurified as a trimethylamine methyl transfer (TMA-MT) activity detected by stimulation of the TMA:CoM methyl transfer reaction in cell extracts. The purified TMA-MT fraction stimulated the rate of methyl-CoM formation sevenfold, up to 1.7 micromol/min/mg of TMA-MT protein. The TMA-MT polypeptides had molecular masses of 52 and 26 kDa. Gel permeation of the TMA-MT fraction demonstrated that the 52-kDa polypeptide eluted with an apparent molecular mass of 280 kDa. The 26-kDa protein eluted primarily as a monomer, but some 26-kDa polypeptides also eluted with the 280-kDa peak, indicating that the two proteins weakly associate. The two polypeptides could be completely separated using gel permeation in the presence of sodium dodecyl sulfate. The corrinoid remained associated with the 26-kDa polypeptide at a molar ratio of 1.1 corrin/26-kDa polypeptide. This polypeptide was therefore designated the TMA corrinoid protein, or TCP. The TMA-MT polypeptides, when supplemented with purified methylcorrinoid:CoM methyltransferase (MT2), could effect the demethylation of TMA with the subsequent methylation of CoM and the production of dimethylamine at specific activities of up to 600 nmol/min/mg of TMA-MT protein. Neither dimethylamine nor monomethylamine served as the substrate, and the activity required Ti(III) citrate and methyl viologen. TMA-MT could interact with either isozyme of MT2 but had the greatest affinity for the A isozyme. These results suggest that TCP is uniquely involved in TMA-dependent methanogenesis, that this corrinoid protein is methylated by the substrate and demethylated by either isozyme of MT2, and that the predominant isozyme of MT2 found in TMA-grown cells is the favored participant in the TMA:CoM methyl transfer reaction.     

In vivo and in vitro acylation of polypeptides in Vibrio harveyi: identification of proteins involved in aldehyde production for bioluminescence.

Incubation of soluble extracts from Vibrio harveyi with [3H]tetradecanoic acid (+ ATP) resulted in the acylation of several polypeptides, including proteins with molecular masses near 20 kilodaltons (kDa), and at least five polypeptides in the 30- to 60-kDa range. However, in growing cells pulse-labeled in vivo with [3H]tetradecanoic acid, only three of these polypeptides, with apparent molecular masses of 54, 42, and 32 kDa, were specifically labeled. When extracts were acylated with [3H] tetradecanoyl coenzyme A, on the other hand, only the 32-kDa polypeptide was labeled. When luciferase-containing dark mutants of V. harveyi were investigated, acylated 32-kDa polypeptide was not detected in a fatty acid-stimulated mutant, whereas the 42-kDa polypeptide appeared to be lacking in a mutant defective in aldehyde synthesis. Acylation of both of these polypeptides also increased specifically during induction of bioluminescence in V. harveyi. These results suggest that the role of the 32-kDa polypeptide is to supply free fatty acids, whereas the 42-kDa protein may be responsible for activation of fatty acids for their subsequent reduction to form the aldehyde substrates of the bioluminescent reaction.     

Accumulation of a Glycoprotein That is Homologous to a Seed Storage Protein in Mung Bean Hypocotyls at the Late Stage of Tissue Elongation

Physiological changes were examined in the amount of a 50-kDaglycoprotein (gp50) that was recovered in a nuclear fractionfrom hypocotyls of mung bean (Vigna radiata) seedlings. Immunoblotanalysis indicated that the glycoprotein was present in hypocotylsand epicotyls from 4- and 5-day-old seedlings but not in hypocotylsfrom 2-day-old seedlings. The glycoprotein was not detectedin leaves or roots. When we divided hypocotyls of 3-day-oldseedlings into the elongating region (0 to 1.5 cm below thecotyledon) and the mature region, we found gp50 in the matureregion only. The results suggest that the 50-kDa glycoproteinis synthesized de novo and accumulates at the late stage duringelongation of cells in the hypocotyl. Furthermore, an antibodyspecific to gp50 reacted with a major 50-kDa protein in cotyledons,which is known as a storage protein in mung bean cotyledon.Eighteen amino acid residues among 22 amino-terminal residuesof gp50 were identical to those of the storage protein fromcotyledon. A peptide map of the glycoprotein after digestionwith V8 protease was similar to that of the storage protein.Overall, our findings suggest that the glycoprotein recoveredin the nuclear fraction is an isoform of the seed storage proteinthat is expressed only in the mature cells of hypocotyls andepicotyls. ⁴ Present address: Bioscience and Chemistry Division, HokkaidoNational Industrial Research Institute, Agency of IndustrialScience and Technology, Sapporo, 062 Japan     

Purification and characterization of ferritins from maize, pea, and soya bean seeds. Distribution in various pea organs

Ferritins from maize, pea, and soya bean seeds were purified. They contain two polypeptides of 28 and 26.5 kDa. The molecular weight of native pea seed ferritin has been estimated to be 540,000. Pea and maize seed ferritins were compared by reverse phase high performance liquid chromatography, amino acid composition, and two-dimensional gel electrophoresis. They are very similar, although four isoforms of the 28-kDa polypeptide from the pea were observed in contrast to a unique polypeptide in maize. No isoforms of the 26.5-kDa polypeptide were detected. Rabbit antibodies were produced in response to pea seed ferritin. It was shown by Western blot analysis that ferritins of the three plants analyzed share immunological determinants. However, horse spleen ferritin was not recognized by the phytoferritin antibodies. Antibodies were also used to demonstrate that ferritins are not uniformly distributed in different pea organs from 30-day-old iron-unloaded plants. The protein was more abundant in flowers than in fruits and roots, and was not detected in leaves.     

Identification of porin-like polypeptide(s) in the boundary membrane of oilseed glyoxysomes

A 36-kDa polypeptide of unknown function was identified by us in the boundary membrane fraction of cucumber seedling glyoxysomes. Evidence is presented in this study that this 36-kDa polypeptide is a glyoxysomal membrane porin. A sequence of 24 amino acid residues derived from a CNBr-cleaved fragment of the 36-kDa polypeptide revealed 72% to 95% identities with sequences in mitochondrial or non-green plastid porins of several different plant species. Immunological evidence indicated that the 36-kDa (and possibly a 34-kDa polypeptide) was a porin(s). Antiserum raised against a potato tuber mitochondrial porin recognized on immunoblots 34-kDa and 36-kDa polypeptides in detergent-solubilized membrane fractions of cucumber seedling glyoxysomes and mitochondria, and in similar glyoxysomal fractions of cotton, castor bean, and sunflower seedlings. The 36-kDa polypeptide seems to be a constitutive component because it was detected also in membrane protein fractions derived from cucumber leaf-type peroxisomes. Compelling evidence that one or both of these polypeptides were authentic glyoxysomal membrane porins was obtained from electron microscopic immunogold analyses. Antiporin IgGs recognized antigen(s) in outer membranes of glyoxysomes and mitochondria. Taken together, the data indicate that membranes of cucumber (and other oilseed) glyoxysomes, leaf-type peroxisomes, and mitochondria possess similar molecular mass porin polypeptide(s) (34 and 36 kDa) with overlapping immunological and amino acid sequence similarities.