Subunit structure and activity of glyceraldehyde-3-phosphate dehydrogenase from spinach chloroplasts

Glyceraldehyde-phosphate dehydrogenase (d-glyceraldehyde-3-phosphate : NADP⁺ oxidoreductase (phosphorylating), EC 1.2.1.13) from spinach chloroplasts is a polymeric protein of approx. 600 000 daltons and sodium dodecyl sulphate gel electrophoresis shows that it consists of two subunits of molecular weight 43 000 and 37 000. Comparison of amino acid analyses and tryptic peptide maps indicates that the two subunits have a different primary structure. The native enzyme contains 0.5 mol of NADP⁺ and 0.5 mol of NAD⁺ per protomer of 80 000 daltons, no reduced pyridine nucleotides have been detected.Almost complete inactivation is obtained by reaction of two cysteinyl residues per 80 000 daltons with tetrathionate or iodo[¹⁴C₂]acetic acid; since the same amount of radioactivity is incorporated in the two subunits it is likely that they are both essential for the catalytic activity.Charcoal stripping of native glyceraldehyde-phosphate dehydrogenase produces an apoprotein which still retains most of the enzymatic activity but, unlike the holoenzyme, is gradually inactivated by storage at 4°C and does not react with iodoacetate under the same conditions in which the holoenzyme is completely inactivated.     

D-Ribulose-1,5-bisphosphate carboxylase/oxygenase from chemolithotrophically grown Rhizobium japonicum

Ribulose-1,5-bisphosphate carboxylase/oxygenase has been purified from chemolithotrophically grown Rhizobium japonicum SR and ribulose-5-phosphate kinase activity has also been detected in extracts of such cells. Electrophoretically homogeneous ribulosebisphosphate carboxylase/oxygenase purified in the presence of PMSF showed two types of large subunits of 55 000 and 53 000 daltons and small subunits of 14 200 daltons. The heterogeneity of large subunits was not observed when the enzyme was prepared in the presence of PMSF and DIFP. Ribulose-1,5-bisphosphate carboxylase from R. japonicum was inhibited by antibodies to this enzyme and a single precipitin band from the antibody-enzyme interaction was observed on double diffusion plates. Antibodies to R. japonicum enzyme did not cross-react on immunodiffusion plates with the ribulosebisphosphate carboxylase/oxygenases from wheat, spinach, soybean and tobacco.     

On the subunit structure of particulate aminopeptidase from pig kidney.

Solubilization of particulate aminopeptidase (EC 3.4.11.2) from pig kidney with Triton X-100 yields an aggregate (mol. wt. approx. 10(6)) that decomposes into "free" aminopeptidase (mol. wt. 280 000) either upon autolysis at pH 5 or after exposure to trypsin. Both procedures yield free enzymes that are identical with respect to electrophoretic mobility, enzymatic activity and zinc content. After dissociation, the enzyme resulting from autolysis yields a single subunit of 140 000 molecular weight while the trypsin-treated enzyme produces three fragments (140 000, 95 000 and 48 000 mol. wt.). As the aggregate is formed by subunits 10 000 daltons heavier than those of the free enzyme, the existence of a hydrophobic portion anchoring the enzyme to the membrane might be postulated. Reactivation experiments carried out on the three purified fragments of urea-denatured aminopeptidase show that the 140 000 molecular weight subunit is the only one able to yield an active enzyme (after spontaneous dimerization). It can be concluded that the smaller fragments are artefacts resulting from trypsin degradation during purification.     

韭菜叶绿体超氧化物歧化酶纯化及性质研究

经硫酸铵沉淀、ＳｅｐｈａｄｅｘＧ－２００凝胶过滤和ＤＥＡＥ－Ｓｅｐｈａｃｅｌ层析３个步骤将韭菜叶绿体ＳＯＤ纯化到均一程度。鉴定该酶是Ｃｕ．Ｚｎ－ＳＯＤ,测得其分子量约３２０００Ｄ,亚基分子量约为１６２００Ｄ,Ｎ－末端氨基酸为Ａｌａ。该酶在紫外与可见光区的吸收峰分别在２６５ｎｍ和６７５ｎｍ。实验表明该酶热稳定性良好。     

Purification and characterization of a Ca2+/calmodulin-dependent protein kinase from rat brain

A soluble Ca2+/calmodulin-dependent protein kinase has been purified from rat brain to near homogeneity by using casein as substrate. The enzyme was purified by using hydroxylapatite adsorption chromatography, phosphocellulose ion-exchange chromatography, Sepharose 6B gel filtration, affinity chromatography using calmodulin-Sepharose 4B, and ammonium sulfate precipitation. On sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gels, the purified enzyme consists of three protein bands: a single polypeptide of 51 000 daltons and a doublet of 60 000 daltons. Measurements of the Stokes radius by gel filtration (81.3 +/- 3.7 A) and the sedimentation coefficient by sucrose density sedimentation (13.7 +/- 0.7 S) were used to calculate a native molecular mass of 460 000 +/- 29 000 daltons. The kinase autophosphorylated both the 51 000-dalton polypeptide and the 60 000-dalton doublet, resulting in a decreased mobility in NaDodSO4 gels. Comparison of the phosphopeptides produced by partial proteolysis of autophosphorylated enzyme reveals substantial similarities between subunits. These patterns, however, suggest that the 51 000-dalton subunit is not a proteolytic fragment of the 60 000-dalton doublet. Purified Ca2+/calmodulin-dependent casein kinase activity was dependent upon Ca2+, calmodulin, and ATP X Mg2+ or ATP X Mn2+ when measured under saturating casein concentrations. Co2+, Mn2+, and La3+ could substitute for Ca2+ in the presence of Mg2+ and saturating calmodulin concentrations. In addition to casein, the purified enzyme displayed a broad substrate specificity which suggests that it may be a "general" protein kinase with the potential for mediating numerous processes in brain and possibly other tissues.     

On the Size of the DNA in the Mammalian Chromosome: Structural Subunits

Alkaline degradation of mammalian DNA indicates that the molecule exists in the chromosome as an array of structural subunits. The size of the subunit of single-stranded DNA is circa 5 × 10⁸ daltons, and it is of sufficient length to contain a number of synthetic units, replicons. The upper size limit of the multicomponent structure is in excess of 10¹⁰ daltons. Mammalian cells of three different origins have been shown to contain the same basic structural DNA components and these components exist throughout the cell cycle. The nature of the links between the subunits is not known.     

Human skin collagenase: isolation of precursor and active forms from both fibroblast and organ cultures.

Human skin procollagenase has been isolated, in pure form, from the medium of fibroblasts cultured in the presence or absence of added serum. Purification was achieved using a combination of cation-exchange (phosphocellulose or carboxymethylcellulose) and gel-filtration chromatography. Two forms (60 000 and 55 000 daltons) of the procollagenase were detected by electrophoresis in sodium dodecyl sulfatepolyacrylamide gels and could be separated by chromatography on Ultrogel AcA-44. Each form was converted to active enzyme by trypsin, producing species of 50 000 and 45 000 daltons, respectively. An autoactivation process also occurred, which yielded active enzyme without a detectable change in molecular weight. Procollagenase also was found in organ cultures of human skin but only when serum was added to the medium. This suggests that a serum-inhibitable proteolytic system is present in these cultures which, like trypsin, converts procollagenase to the active enzyme forms that can be isolated from serum-free organ culture medium. The collagenase species obtained from either fibroblast or organ culture medium were chromatographically and electrophoretically identical.     

Purification and properties of citrate lyase from Escherichia coli

Citrate lyase (EC 4.1.3.6) has been purified from Escherichia coli and the homogeneity of the preparation established from the three-component subunits obtained on sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The purified enzyme has a specific activity of 120 mumol min-1 mg-1 and requires optimally 10 mM Mg2+ and a pH of 8.0 for the cleavage reaction. The native enzyme is polydispersed in the ultracentrifuge and in polyacrylamide gel electrophoresis. The enzyme complex is composed of three different polypeptide chains of 85 000, 54 000, 32 000 daltons. An estimate of subunit stoichiometry indicates that 1 mol of the largest polypeptide chain is associated with 6 mol each of the smaller ones. The polypeptide subunits have been isolated in pure state and their biological functions characterize. The 54 000-dalton subunit functions as the acyltransferase alpha subunit catalyzing the formation of citryl coenzyme A from citrate in the presence of acetyl coenzyme A and ethylenediaminetetraacetic acid. The 32 000-dalton subunit functions as the acyllyase beta subunit catalyzing the cleavage of (3S)-citryl coenzyme A to oxal-acetate and acetyl coenzyme A. The 85 000-dalton subunit, which carries exclusively the prosthetic group components, functions as the acyl-carrier protein gamma subunit in the cleavage of citrate in the presence of mg2+ and the alpha and beta subunits. The presence of a large ACP subunit and the unusual stoichiometry of the different subunits distinguish the complex from other citrate lyases. A ligase which acetylates the deacetyl[citrate lyase] in the presence of acetate and ATP has ben shown to be present in the organism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies of the structure of fructose-6-phosphate 2-kinase:fructose-2,6-bisphosphatase

Some physicochemical properties of a homogeneous preparation of a bifunctional enzyme, fructose-6-phosphate 2-kinase:fructose-2,6-bisphosphatase, were determined. The molecular weight of the enzyme is 101 000 as determined by high-speed sedimentation equilibrium. The molecular weight of dissociated enzyme is 55 000 in 6 M guanidinium chloride by sedimentation equilibrium and in sodium dodecyl sulfate by polyacrylamide gel electrophoresis. A value of 4.7 was observed for the isoelectric point. Tryptic peptide maps and high-performance liquid chromatography of the trypsin-digested enzyme revealed approximately 60 peptides. Amino acid analysis of the enzyme shows that it contains 27 lysine and 36 arginine residues per 55 000 daltons. No free N-terminal amino acid residue was detectable, suggesting that it is blocked. Hydrolysis of the enzyme by carboxypeptidases A and B releases tyrosine followed by histidine and arginine, indicating that the amino acid sequence at the carboxyl terminus is probably -Arg-His-Tyr. Tryptic digestion of [32P]phosphofructose-6-phosphate 2-kinase:fructose-2,6-bisphosphatase yields a 32P-labeled peptide detected by tryptic peptide mapping and high-performance liquid chromatography. Thermolysin digestion of CNBr-cleaved 32P-enzyme also yields a single 32P-peptide. These results indicate that fructose-6-phosphate 2-kinase:fructose-2,6-bisphosphatase is a dimer of 55 000 daltons and the subunits are very similar, if not identical.     

Biosynthesis and degradation of gamma-glutamyltranspeptidase of rat kidney

gamma-Glutamyltranspeptidase (gamma GTP) of rat kidney is an intrinsic glycoprotein bound to the plasma membrane and composed of two nonidentical subunits and an amino-terminal portion of the heavy subunit anchors the enzyme to the membrane. The mechanisms of biosynthesis, post-translational processing and degradation of the enzyme were studied using mono-specific antibody raised to gamma-glutamyltranspeptidase purified from rat kidney. The following results were obtained. Double isotope labeling in vivo showed that gamma-glutamyltranspeptidase is synthesized as a precursor form with a single polypeptide chain of 78,000 daltons, and then processed post-translationally by limited proteolysis, resulting in two subunits of 50,000 and 23,000 daltons. Incorporation of [3H]leucine or [35S]methionine into the precursor form increased until 60 min after their intravenous injection, and a pulse-chase experiment showed that the half life of the precursor form was 53 min. [3H]Fucose and [3H]glucosamine could also be incorporated into the precursor form, showing that glycosylation of the enzyme occurs at the stage of the precursor form. Rat kidney labeled with [3H]fucose was subjected to subcellular fractionation. The Golgi fraction contained the glycosylated precursor form and a small amount of subunits, and the plasma membrane fraction contained mostly subunits with a significant amount of precursor, suggesting that post-translational processing of the precursor occurs on the plasma membrane. The apparent half lives of the native enzyme and the heavy and light subunits were all estimated as 4.3 +/- 0.5 days by labeling with [3H]leucine or [3H]fucose. gamma-Glutamyltranspeptidase has a different turnover rate from aminopeptidase M, which is located in the microvillus membrane close to gamma-glutamyltranspeptidase.     

The subunit structures of soluble and chromatin-bound RNA polymerase II from soybean

DNA-dependent RNA polymerase II is present in two forms, IIa and IIb, in germinating soybean. Form IIa is the dominant form of the enzyme in ungerminated embryos and appears to be a soluble enzyme. Form IIb increases in amount as germination progresses and is tightly bound to the chromatin template. The subunit structures of soybean RNA polymerases IIa and IIb are identical except for the molecular weights of their largest subunits which are 200,000 daltons and 170,000 daltons for IIa and IIb, respectively. The enzymes have seven common subunits: 142,000, 42,000, 26,000, 20,000, 16,000, 15,000, and 14,000 daltons.     

Vanadate promotes photooxidative cleavage and inactivation of muscle phosphofructokinase

During irradiation in the presence of decavanadate, the subunits of phosphofructokinase underwent progressive degradation to a fragment of about 78,000 daltons. This cleavage pattern was altered when the photoirradiation was performed in the presence of monomeric vanadate with formation of several smaller peptides. The specificity of the decavanadate induced cleavage was proved by the resistance of other enzymes to the treatment and by the effects of phosphofructokinase ligands. During irradiation, the activity of the enzyme declined. Differences between the rate of inactivation and of cleavage of enzyme subunits suggest the occurrence of multiple processes.     

赤子爱胜蚓超氧化物歧化酶的纯化和部分性质研究

采用硫酸铵分级沉淀和柱层析的方法,从赤子爱胜蚓整体细胞抽提液内分离得到纯的铜锌超氧化物岐化酶（Ｃｕ,Ｚｎ－ＳＯＤ）。每１００ｇ蚯蚓得到的ＳＯＤ制品,总活力为１１１５０Ｕ,比活力为５１３８Ｕ／ｍｇ蛋白,回收率为２０％。铜锌超氧化物岐化酶呈淡蓝绿色,最大紫外吸收波长为２７０ｎｍ。测得该酶分子量为３３０００,亚基分子量为１６５００。该酶亚基由１５６个氨基酸残基组成,不含酪氨酸。     

Subunits of cytochrome a-type terminal oxidases derived from Thiobacillus novellus and Nitrobacter agilis.

Cytochrome a-type terminal oxidases derived from Thiobacillus novellus and Nitrobacter agilis have been purified to a homogeneous state as judged from their electrophoretic behavior and their subunit structures studied by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The T. novellus enzyme is composed of two kinds of subunits of 32,000 and 23,000 daltons and its minimum molecular weight is 55,000 on the basis of heme content and amino acid composition. The N. agilis enzyme also has two kinds of subunits of 40,000 and 27,000 daltons and its minimum molecular weight is 66,000 on the basis of heme content and amino acid composition. Therefore, the molecule of each enzyme is composed of two kinds of subunits which resemble the subunits of the eukaryotic cytochrome oxidase biosynthesized in the mitochondrion at least with respect to molecular weight.     

Properties of catalase purified from a methanol-grown yeast, Kloeckera sp. 2201

Catalase, a marker enzyme of peroxisomes, was purified to homogeneity from whole cells of Kloeckera sp. 2201 (a strain of Candida boidinii) grown on methanol by means of ammonium sulfate fractionation followed by hydroxyapatite, Sephacryl S-300 and DEAE-Sepharose column chromatographies. Crystallized catalase was brown-coloured and needle-like. The molecular mass of the enzyme was about 240 000 daltons consisting of four identical subunits of 62 000 daltons. The minimum size of catalase molecule was estimated to be about 6 X 10 nm from an electron micrograph. Judging from the absorption spectrum, the enzyme seemed to belong to a group of T-type catalase. The Km value of the enzyme for hydrogen peroxide (catalatic activity) was 25 mM, while that for methanol (peroxidatic activity) was 83 mM. Catalase from Kloeckera sp. cells showed a certain degree of similarity to the enzyme purified from alkane-grown Candida tropicalis [T. Yamada et al. (1982) Eur. J. Biochem. 125, 517-521 and 129, 251-255] in its immunochemical properties.     

Purification and properties of NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase from spinach leaves

An NAD⁺-dependent glyceraldehyde-3-phosphate dehydrogenase (d-glyceraldehyde-3-phosphate:NAD⁺ oxidoreductase (phosphorylating), EC. 1.2.1.12) has been purified from spinach leaves as a homogeneous protein of 150 000 daltons.Kinetic constants of 2.5·10⁻⁴ M and 4 · 10⁻⁴ M have been calculated for NAD⁺ and glyceraldehyde 3-phosphate, respectively.The amino acid composition is characterized by a cysteine content higher than that found in analogous enzymes.On sodium dodecyl sulphate gel electrophoresis, the native enzyme dissociates into two subunits of 37 000 and 14 000 daltons. The two subunits have been isolated in equimolar amounts by gel filtration; end-group analysis shows that alanine is the N-terminal residue of the large subunit, while serine is found at the N-terminus of the small subunit.Comparison of amino acid analyses and peptide maps shows that the two subunits have a different amino acid sequence. These results indicate that the NAD⁺-dependent glyceraldehyde-3-phosphate dehydrogenase, isolated from spinach leaves has an atypical oligomeric structure, the protomer being formed by two different subunits.     

Carboxamidopeptidase: purification and characterization of a neurohypophyseal hormone inactivating peptidase from toad skin

Carboxamidopeptidase, an enzyme which inactivates neurohypophyseal hormones, has been purified 3800-fold in an overall yield of 22% from toad skin, a neurohypophyseal hormone target organ, by (NH4)2SO4 fractionation, DEAE-Sephadex chromatography, and affinity chromatography on immobilized p-aminobenzamidine and concanavalin A-agrose. The purified enzyme is capable of inactivating both [8-arginine]vasopressin (AVP) and oxytocin by hydrolyzing the Arg8-Gly9-NH2 and the Leu8-Gly9-NH2 bonds, respectively, and can hydrolyze the ester substrates, benzoyl-L-arginine ethyl ester (BzArgOEt) and acetyl-L-trypsine ethyl ester, suggesting that the enzyme has both trypsin-like and chymotrypsin-like activities. Carboxamidopeptidase is maximally active at pH 7.5-8.5 for AVP and BzArgOEt and pH 7.0 for oxytocin. Carboxamidopeptidase is inhibited by ovoinhibitor, ovomucoid, Trasylol. lima bean trypsin inhibitor, concanavalin A, antipain, leupeptin, chymostatin, elastatinal, p-nitrophenyl p-guanidinobenzoate, and 4-methylumbelliferyl p-guanidinobenzoate but not by soybean trypsin inhibitor, alpha 1-antitrypsin, hirudin, pepstatin, bestatin, phosphoramidon, or cysteine. The enzyme is also inhibited by the serine protease inhibitor, diisopropyl phosphofluoridate (i-Pr2PF), and by the chloromethyl ketone derivatives of tosyllysine, tosylphenylalanine, and (benzyloxycarbonyl)phenylalanine, as well as by the sulfhydryl group reagent, p-(chloromercuri)benzoate (PCMB). Inhibition by PCMB is reversed by cysteine. The molecular weight determined by gel filtration in the presence of 1 MNaCl is approximately 100 000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that the enzyme is composed of two identical subunits of 48 000 daltons. Each subunit consists of a heavy chain (28 000 daltons) and a light chain (19 000 daltons) joined by a disulfide bond(s). Labeling experiments using [3H]-i-Pr2PF showed that the enzyme active site is located in the heavy chain.     

5-Oxoprolinase from rat kidney, II. Molecular weight determinations.

The molecular weight of 5-oxoprolinase from rat kidney was estimated by gel filtration on Sephadex G-200 and G-150 to be 460 000 +/- 30 000. A value of 230 000 +/- 10 000 was obtained by zonal sedimentation in a sucrose gradient. Polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate yielded a molecular weightof 115 000 +/- 6 000. It is concluded that 5-oxoprolinase consists of four subunits of 115 000 daltons each. The dissociation or aggregation behavior of the enzyme seems to be influenced neither by the presence of the substrates 5-oxo-L-proline and MgATP2theta nor by the presence of the stabilizing compounds glutathione mercaptoethanol or dithioerythritol.     

蚯蚓体内超氧化物歧化酶分析

蚯蚓体内SOD含量甚高,35℃饲养的蚯蚓其SOD比活最高,因此,纯化前将蚯蚓在35℃养殖4周以上.采用硫酸铵分级沉淀和柱层析的方法,从蚯蚓体内分离得到纯的铜锌超氧化物歧化酶.每100g组织得到SOD制品总活力为17,190 U,比活7995 U/mg,回收率为35%.该酶呈淡蓝绿色,最大紫外吸收波长为270nm.该酶分子量为33,000,亚基分子量为16,500.该酶亚基含156个氨基酸残基,不含酪氨酸.N-末端为丙氨酸,等电聚焦为三条谱带,等电点分别为5.30 、5.59和6.22.     

Limited proteolysis of nitrate reductase purified from membranes of Escherichia coli.

The heterogeneous form of nitrate reductase released from the membrane fraction of Escherichia coli by heat treatment was converted to a new electrophoretic form by incubation with trypsin. As a result of the trypsin treatment, the heat-released enzyme was converted from an associating-dissociating system to a nonassociating monomer (Mr approximately 200,000) which retained full enzymatic activity. Several distinct subunits in the 47,000- to 59,000-dalton range were converted to a single 43,000-dalton subunit during the trypsin treatment, while the other major subunit (155,000 daltons) was unaffected. Nitrate reductase extracted from the membrane fraction with deoxycholate and ammonium sulfate was composed of two apparently homogeneous subunits (155,000 and 59,000 daltons). The detergent-extracted enzyme preparation was converted by trypsin to an electrophoretic form very similar to the product of trypsin treatment of the heat-released enzyme with an identical subunit composition (155,000 and 43,000 daltons). These results demonstrate that the heterogeneous subunits present in the heat-released enzyme are produced during heat treatment by proteolytic cleavage of a single 59,000-dalton subunit. The fragments removed by trypsin treatment are implicated in the self-associating properties of the heat-released enzyme.