Isolation of a 240-kilodalton actin-binding protein from Dictyostelium discoideum

A high molecular weight actin-binding protein with subunit mass of 240 kilodaltons has been purified from vegetative amoebae of Dictyostelium discoideum. Briefly, a cell extract was prepared by homogenizing vegetative amoebae in 5 mM EGTA, 5 mM 1,4-piperazineethanesulfonic acid, 1 mM dithiothreitol, 0.02% NaN3, pH 7.0, followed by ultracentrifugation at 114,000 X g for 1 h. The 240-kDa protein in this extract was separated from actin by chromatography on ATP-saturated DEAE-cellulose and further purified by chromatography on hydroxylapatite and Sephacryl S-300. The 240-kDa protein increases the low shear viscosity of F-actin. Covalent cross-linking with dimethyl suberimidate demonstrates that the 240-kDa protein can form dimers in high salt (500 mM NaCl). Hydrodynamic studies in high salt demonstrate the presence of an asymmetric dimer (Stokes' radius = 8.6 nm, sedimentation coefficient = 12 S, native molecular weight = 434,000, and frictional ratio = 1.7). Rotary shadowing demonstrates that the monomer is a flexible rod of approximately 70 nm in length that can associate end to end to form a dimer of approximately 140 nm in length. The 240-kDa protein cross-reacts with antibodies to chicken gizzard filamin. The properties of the 240-kDa protein suggest that it is a member of the filamin class of actin-associated proteins.     

Control of glycoprotein synthesis. Purification of UDP-N-acetylglucosamine:alpha-D-mannoside beta 1-2 N-acetylglucosaminyltransferase II from rat liver

A new affinity chromatography adsorbant, in which UDP-GlcNAc has been linked to thiopropyl-Sepharose at the 5 position of the uracil via a 5-mercuri mercaptide bond, was utilized to purify UDP-GlcNAc:alpha-D-mannoside beta 1-2 N-acetylglucosaminyltransferase II 60,000-fold from rat liver. After extraction of rat liver membranes with Triton X-100, the enzyme was found to exist in two molecular weight forms of markedly differing size, separable on Sephadex G-200. The low Mr form was separated from the high Mr form on columns of CM-Sephadex and hydroxylapatite, and was further purified by sequential elutions with NaCl, UDP-GlcNAc, and EDTA from the 5-mercuri-UDP-GlcNAc affinity adsorbant. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified low Mr form under reducing conditions revealed two protein bands of Mr 48,000 and 43,000. The purified enzyme catalyzes the transfer of N-acetylglucosamine from UDP-GlcNAc to the compound: (Formula: see text) The high Mr form of the enzyme, which eluted in the void volume of Sephadex G-200, was resistant to a number of treatments in attempts to reduce its molecular weight. These results suggest that the high Mr form of the enzyme may represent either a complex which normally exists in Golgi membranes as a result of strong protein-protein interactions or a protein with one or more "anchor" segments.     

Purification and characterization of an F-actin-bundling 55-kilodalton protein from HeLa cells

An F-actin-bundling protein with Mr of 55,000 has been purified from HeLa cells by a simple method using its affinity to F-actin. Briefly, muscle actin was mixed with supernatants of HeLa cell homogenates, and the resultant actin gel was precipitated by low speed centrifugation. The 55-kDa protein in the actin gel was dissociated by depolymerization of F-actin and purified sequentially by chromatography on DEAE-cellulose and hydroxylapatite. The Stokes radius and sedimentation coefficient of the 55-kDa protein were 32 A and 4.35 (S20,w), respectively. These results suggest that the 55-kDa protein is a monomeric globular protein with a native molecular weight of 57,000. The globular form of the protein was confirmed by electron microscopy of rotary shadowed specimens. The binding of the protein to actin was saturated at an approximate stoichiometry of 4 actin monomers to one 55-kDa molecule. The protein made F-actin aggregate side-by-side into bundles as has been reported for other F-actin-bundling proteins such as fimbrin (Mr = 68,000) and fascin (Mr = 58,000). The 55-kDa protein is a new actin-binding protein based on biochemical, morphological, and immunological characterization. Skeletal muscle tropomyosin inhibited the actin-bundling activity of 55-kDa protein by competitive binding to actin, suggesting that the 55-kDa protein binding site on F-actin is in the vicinity of the tropomyosin-binding site.     

Purification and Properties of Dextransucrase from Streptococcus mutans

The dextransucrase (EC 2.4.1.5) activity from cell-free culture supernatants of Streptococcus mutans strain 6715 has been purified approximately 1,500-fold by ammonium sulfate precipitation, hydroxylapatite chromatography, and isoelectric focusing. The enzyme was eluted as a single peak of activity from hydroxylapatite, and isoelectric focusing of the resulting preparation gave a single band of dextransucrase activity which focused at a pH of 4.0. The final enzyme preparation contained two distinct, enzymatically active proteins as judged by assay in situ after polyacrylamide gel electrophoresis. One of the proteins represented 90% of the total dextransucrase activity and 53% of the total protein. The molecular weight of the enzyme was estimated by gel filtration to be 94,000. The temperature optimum of the enzyme was broad (34 to 42 C) and its pH range was rather narrow, with optimal activity at pH 5.5. The K(m) for sucrose was 3 mM, and fructose competitively inhibited the enzyme reaction with a K(i) of 27 mM.     

Two binding proteins for progesterone in the bovine corpus luteum

The cytosolic supernatant of bovine corpus luteum contains two proteins which bind progesterone specifically. Bovine luteal cytosol was fractionated on hydroxylapatite and the peaks of protein obtained subjected to equilibrium dialysis against progesterone. Progesterone-binding activities (Ka approx. 10(6) 1/mol) was eluted at 40 mM (Binding Protein 1) and 100 mM phosphate (Binding Protein 2). They sedimented differently (3.95 and 4.65, respectively) on sucrose gradients. In contrast to Binding Protein 1, Binding Protein 2 bound R5020 better than progesterone on sucrose gradients. Purification of the binding activity eluted by 40 mM phosphate from the hydroxylapatite column showed that it resided in a single protein (molecular weight 65,000 daltons). The function of these proteins is presently unknown, but they may participate in the biosynthesis and/or secretion of progesterone from bovine luteal cells.     

Application of high-performance ion-exchange chromatography to the analysis of cytosolic glucocorticoid receptor

The use of high-performance ion-exchange chromatography (HPIEC) on a Mono Q column was investigated for the analysis of glucocorticoid receptor. In the presence of 10 mM sodium molybdate, both liganded and unliganded glucocorticoid receptor were eluted as a single and sharp peak (0.32 M NaCl). In the absence of molybdate and after exposure to heat and salt, another peak of specifically bound radioactivity was eluted with 0.08 M NaCl. When HPIEC was performed in the absence of molybdate, two molecular forms of the liganded receptor were detected which eluted with 0.08 M NaCl (Stokes' radius Rs = 5.1 nm, s20,w = 4.6 S, calculated mol. wt Mr approximately 100,000) and 0.32 M NaCl (Rs = 7.3 nm, S20,w = 9.0 S, calculated Mr approximately 280,000). Analysis of both forms with mini-columns of DNA-Ultrogel, DEAE-Trisacryl and hydroxylapatite (HA-Ultrogel) confirmed the identity of the two peaks with transformed and non-transformed glucocorticoid-receptor complexes. These results suggest that HPIEC may provide a useful tool for the rapid resolution and quantification of receptor molecular forms.     

The separation and characterization of two forms of Torpedo electric organ calelectrin

Two methods for extracting calelectrin, a Ca2+-regulated membrane-binding protein from the electric organ of Torpedo marmorata, have been compared and the more promising one was modified to increase the yield to 7-8 mg.kg-1 wet weight of tissue, that is 4-5 times greater than the original method. The calelectrin so obtain could be resoloved into a minor component (designated L-calelectrin) eluted from an anion-exchange column at relatively low ionic strength (100 mM NaCl) and a major component (H-calelectrin) eluted at higher ionic strength (300 mM NaCl). The two forms were also separated by chromatography on a hydrophobic resin. Electrophoresis on cellulose acetate indicated that L-calelectrin had a lower mean isoelectric point that the H-form and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate showed that under reducing conditions (presence of 5% beta-mercaptoethanol) both forms migrated as single species, the L-form having a lower apparent relative molecular mass (Mr 32,000) that the H-form (34,000). Under non-reducing conditions, there was no change in the migration of L-calelectrin but the H-form was resolved into two components of Mr 34,000 and 32,000. The addition of 2 mM Ca2+ had no effect on the migration of either form. Both forms were equally recognized by an anti-calelectrin antiserum and were microheterogeneous with respect to their isoelectric points (pH 4.3-5.5) in two-dimensional gel electrophoresis. Physical measurements were carried out on the major H-form. The Stokes radius was estimated to be 3nm, corresponding to an apparent Mr of 44,000. It was unaffected by changes in ionic strength, pH or Ca2+ concentration. Analytical ultracentrifugation gave a sedimentation constant of 2.9 S and an apparent Mr of 36,000. Measurements of circular dichroism indicated that 78% of the molecule was in the alpha-helix configuration and 22% in random coil. Ca2+ had no significant effect on the conformation.     

Purification and characterization of an isoform of protein kinase C from bovine neutrophils

Protein kinase C (PKC) from bovine neutrophils was purified 1420-fold. Subcellular fractionation analysis of bovine neutrophil homogenate in the presence of EGTA indicated that more than 95% of the PKC activity was present in the soluble fraction. The purification procedure from cytosol involved sequential chromatographic steps on DE-52 cellulose, Mono Q, and phenyl-Sepharose. Whereas bovine brain PKC could be resolved into four isoenzymatic forms by chromatography on a hydroxylapatite column, bovine neutrophil PKC was eluted in a single peak, suggesting that it corresponded to a single isoform. The apparent molecular weight of bovine neutrophil PKC was 82,000, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By filtration on Sephadex G-150, a molecular weight of 85,000 was calculated, indicating that bovine neutrophil PKC in solution is monomeric. Its isoelectric point was 5.9 +/- 0.1. Bovine neutrophil PKC was autophosphorylated in the presence of [gamma-32P]ATP, provided that the medium was supplemented with Mg2+, Ca2+, phosphatidylserine, and diacylglycerol; phorbol myristate acetate could substitute for diacylglycerol. Autophosphorylated PKC could be cleaved by trypsin to generate two radiolabeled peptides of Mr 48,000 and 39,000. The labeled amino acids were serine and threonine. During the course of the purification procedure of bovine neutrophil PKC, a protein of Mr 23,000, which was abundant in the cytosolic fraction of the homogenate, was found to exhibit a strong propensity to PKC-dependent phosphorylation in the presence of [gamma-32P]ATP, Mg2+, Ca2+, phosphatidylserine, and diacylglycerol. This protein was recovered together with PKC in one of the two active peaks eluted from the Mono Q column at the second step of PKC purification.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification and initial characterization of a protein from skeletal muscle that caps the barbed ends of actin filaments

We describe herein the purification of a protein from skeletal muscle that binds to ("caps") the morphologically defined barbed end of actin filaments. This actin-capping protein appeared to be a heterodimer with chemically and immunologically distinct subunits of Mr = 36,000 (alpha) and 32,000 (beta), Rs = 37 A, s20,w = 4.0 S, and a calculated native molecular weight of approximately 61,000. The protein was obtained in milligram quantities at greater than 95% purity from acetone powder of chicken skeletal muscle by extraction in 0.6 M KI, precipitation with ammonium sulfate, sequential chromatographic steps on DEAE-cellulose, hydroxylapatite, and Sephacryl S-200, followed by preparative rate zonal sucrose density gradient centrifugation. In immunoblots of myofibrillar proteins, affinity-purified antibodies selectively recognized protein bands of the same molecular weight as the subunits of the capping protein to which they were made, indicating that the isolated capping protein is a native myofibrillar protein, and not a proteolytic digestion product of a larger muscle protein. A specific interaction of the capping protein with the barbed end of actin filaments was indicated by its ability to inhibit actin filament assembly nucleated by spectrin-band 4.1-actin complex in 0.4 mM Mg2+, accelerate actin filament formation and increase the critical concentration of actin in 2-5 mM Mg2+, 75-100 mM KCl, and inhibit the addition of actin monomers to the barbed end of heavy meromyosin-decorated actin filaments as determined by electron microscopy. All of these effects occurred at nanomolar concentrations of capping protein and micromolar concentrations of actin, suggesting a high affinity interaction.     

Structural characterization of cardiac protein phosphatase with a monoclonal antibody. Evidence that the Mr = 38,000 phosphatase is the catalytic subunit of the native enzyme(s)

The native structures of protein phosphatases have not been clearly established. Several tissues contain high molecular weight enzymes which are converted to active species of Mr approximately 35,000 by denaturing treatments or partial proteolysis. We have used a monoclonal antibody directed against purified bovine cardiac Mr = 38,000 protein phosphatase to determine whether this species is the native catalytic subunit or a proteolytic product of a larger polypeptide. Monoclonal antibody was obtained from a cloned hybrid cell line produced by the fusion of Sp2 myeloma cells with spleen cells from a mouse immunized with phosphatase coupled to hemocyanin. This antibody was specific for the Mr = 38,000 phosphatase as determined by immunoblot analysis of purified enzyme or cardiac tissue extracts after native or sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A single immunoreactive protein of Mr = 38,000 was present in cardiac tissue extracts including extracts prepared from freeze-clamped rat heart rapidly denatured in hot sodium dodecyl sulfate buffer. Precipitation of cardiac extract with 80% ethanol did not alter the Mr of the phosphatase nor did it liberate new immunoreactive material not observed in the extract. Ethanol precipitation caused the dissociation of both phosphatase activity and immunoreactivity from a high Mr form to a form of Mr between 30,000 and 40,000. An immunoreactive protein of Mr = 38,000 was identified in several bovine and rat tissues as well as tissues from rabbits, mice and chickens and human HT-29 cells. From these data we conclude that the Mr = 38,000 cardiac phosphatase is a native catalytic subunit of higher molecular complexes which are dissociated by ethanol precipitation. A very similar, or identical, protein is present in several tissues and species suggesting that this catalytic subunit is a ubiquitous enzyme important in many dephosphorylation reactions.     

Tissue inhibitor of metalloproteinases. Identification of precursor forms synthesized by human fibroblasts in culture

Precursor forms of the glycoprotein tissue inhibitor of metalloproteinases (TIMP) synthesized by human fibroblasts in culture have been identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of specific immunoprecipitates. Translation of mRNA extracted from fibroblasts in the cell-free rabbit reticulocyte lysate system yielded a single immunoprecipitable precursor of tissue inhibitor of metalloproteinases, Mr 22000. Intact fibroblasts cultured in the presence of tunicamycin synthesized an Mr 20 000 form of tissue inhibitor of metalloproteinases, detectable intracellularly and extracellularly. This is in contrast to the predominantly intracellular Mr 24 000 form synthesized during monensin treatment of cells and the normal secreted form of tissue inhibitor of metalloproteinases, Mr 29 000. Isoelectric focusing of the various immunoprecipitable precursor forms showed a progressive increase in positive charge and microheterogeneity of the protein during cellular processing. The data suggest that the inhibitor protein core, of basic pI, is glycosylated initially by the addition of mostly neutral sugars and subsequently by acidic sugars, prior to secretion.     

Localization of sulfated glycoprotein-2 (clusterin) on spermatozoa and in the reproductive tract of the male rat

Sulfated glycoprotein-2 (SGP-2) is one of the major proteins secreted by rat Sertoli cells and epididymal cells in culture. The disulfide-linked dimeric protein secreted by Sertoli cells and found in seminiferous tubule fluid is composed of monomers of Mr 47 000 and 34 000 whereas the epididymal protein exhibits monomers of Mr 40 000 and 29 000. When both forms were chemically or enzymatically deglycosylated, they yielded proteins of similar molecular weight. No modification of the higher molecular weight testicular form by epididymal cells or fluids could be detected in incubation media. SGP-2 mRNA was localized in epididymal epithelium by in situ hybridization. Northern blot analysis indicated the testicular and epididymal mRNAs were of similar size. These findings suggest that the two forms of the protein occur because of tissue-specific post-translational modifications. The detergent-extracted protein from washed testicular spermatozoa is of the higher molecular weight form while epididymal sperm carry the lower molecular weight form. Immunohistochemical evidence suggests that the testicular form is removed prior to the initial segment of the epididymis and the epididymal form is applied in the proximal caput epididymidis. SGP-2 was immunolocalized to the sperm membrane at the ultrastructural level and was distinctly different from the immunolocalization of outer dense fiber proteins and fibrous sheath proteins.     

Calcium-activated, phospholipid-dependent protein kinases from rat liver: subcellular distribution, purification, and characterization of multiple forms

Three forms of Ca2+- and phospholipid-dependent protein kinase (protein kinase C) were extensively purified from rat liver homogenate. Subcellular fractionation analysis indicated that the majority (approximately 85%) of the activity was associated with particulate fractions of the liver. Among these, the microsomal and nuclear fractions accounted for approximately 63% and approximately 10% of total activity. The remaining 15% of protein kinase C was recovered in the soluble fraction following differential centrifugation. It was also found that most of the membrane-associated protein kinase C was latent, with 4-6-fold stimulation with detergents such as 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate, octyl beta-glucoside, or Triton X-100. The activity of both the bound form and the soluble enzyme was enhanced by the addition of Ca2+ and phosphatidylserine, when histone H1 was used as substrate. The bound protein kinase C activity was dissociated by homogenization of liver in buffer containing ethylene glycol bis(beta-aminoethyl ether)-N,-N,N',N'-tetraacetic acid, ethylenediaminetetraacetic acid, and various proteolytic inhibitors, and the solubilized extract was used to purify multiple forms of the enzyme. The purification procedure sequentially utilized (NH4)2SO4 fractionation, ion-exchange chromatography on DEAE-cellulose, gel permeation chromatography on Fractogel TSK HW-55 (F), ion-exchange chromatography on hydroxylapatite, gel permeation chromatography on Ultrogel AcA34, and affinity chromatography on polyacrylamide-immobilized phosphatidylserine. On hydroxylapatite columns, protein kinase C activity was resolved into three isoenzymic forms designated C-I, C-II, and C-III. The molecular weights of the three isoenzymic forms were in the range of 208,000-225,000 as shown by chromatography on calibrated Ultrogel AcA34 columns and sucrose density gradient centrifugation. Furthermore, all three isoenzymes demonstrated a single peak with a sedimentation coefficient (s20.w) in the range of 9.0-9.2. However, with polyacrylamide gel electrophoresis, all the forms showed a single protein component with average molecular weight of 64K, suggesting that the native isoenzymes may be composed by subunits. Finally, all three isoenzymes exhibited nearly identical enzymatic properties.     

Biochemical and immunological analysis of an abundant form of glutathione S-transferase,in mouse testis

One of the major forms of glutathione S-transferase (designated as Ft transferase) has been identified and purified to near homogeneity from mouse testis. The purification was achieved by ammonium sulfate fractionation, DEAE cellulose chromatography, hydroxylapatite chromatography and the preparative isoelectric focusing. Purified Ft transferase has an isoelectric point of 4.9 ± 0.3 and was shown to be a homodimer with a native molecular weight of about 50 000.Immunologically, antisera to Ft transferase do not crossreact with F2 or F3 transferase. However, a weak cross reactivity was observed between the antisera to F3 transferase and Ft transferase. Biochemical properties of purified Ft transferase are similar to those transferases isolated from mouse liver. Tissue distributions of the multiple forms of glutathione S-transferase were examined by column isoelectric focusing of various mouse tissue homogenates. It was found that mouse Ft transferase is present only in testis as a major form and in brain as a minor form, but not in other tissues that were examined.     

Direct evidence for methylation of arginine residues in high molecular weight forms of basic fibroblast growth factor.

Basic fibroblast growth factor (bFGF) is a heparin-binding angiogenic polypeptide mitogen. Protein sequence analysis of bFGF isolated from tissue sources initially established that it is composed of 146 amino acids (apparent Mr 18,000). More recently larger apparent molecular weight forms have been identified and partially characterized. In addition, these high molecular weight forms (apparent Mr 22,000 and 25,000) have been shown to localize preferentially to nuclear fractions of transfected cells. In this report we demonstrate that the higher molecular weight, amino terminally extended forms of bFGF contain methylated arginine residues. The demonstration is based on 1) amino acid sequence analysis of a protein known to contain methylated arginine (myelin basic protein) and a comparison with amino acid sequence analysis of trypsin-derived fragments of the high molecular weight bFGF purified from guinea pig brain and 2) the ability to label in vivo the high molecular weight forms of bFGF with S-adenosyl-L-(methyl-3H)-methionine, the substrate of arginine-protein methylase I. These results are suggestive of a role of arginine methylation in directing nuclear localization of certain forms of bFGF.     

Monocarboxylate and alpha-ketoglutarate carriers from bovine heart mitochondria. Purification by affinity chromatography on immobilized 2-cyano-4-hydroxycinnamate

2-Cyano-4-hydroxycinnamate was covalently linked, through a diazo bond, to Sepharose 4B, which had been elongated with a hydrophobic spacer. A Triton X-100 extract from bovine heart mitochondria was pre-purified by hydroxylapatite chromatography and passed through the 2-cyano-4-hydroxycinnamate affinity resin in the presence of 0.7% deoxycholate. At pH 6 and in the presence of 0.2 M sodium chloride, a single polypeptide with an Mr of 34,000 was eluted. Subsequently, at pH 8 and in the presence of 2-cyano-4-hydroxycinnamate, another single protein with an Mr of 31,500 was released. Both proteins were reconstituted into phospholipid vesicles and their transport activities were measured. High, delta pH-dependent, 2-cyanocinnamate-sensitive pyruvate uptake was measured in vesicles containing only the 34-kDa protein. alpha-Ketobutyrate and other alpha-ketomonocarboxylic acids were competitive inhibitors of the pyruvate uptake, whereas di- and tricarboxylates had only small effects. alpha-Ketoglutarate-alpha-ketoglutarate exchange could only be measured in vesicles containing the 31.5-kDa protein. The molecular weight of this protein and its functional properties were similar to those of the alpha-ketoglutarate carrier isolated by a different method (Bisaccia, Indiveri, C., and Palmieri, F. (1985) Biochim. Biophys. Acta 810, 362-369). 2-Cyano-4-hydroxycinnamate inhibited the alpha-ketoglutarate exchange in a noncompetitive manner with an apparent Ki of 0.7 mM. It is concluded that by the described affinity chromatography procedure, two mitochondrial carriers transporting alpha-ketoacids, i.e. the monocarboxylate and the alpha-ketoglutarate carrier, could be purified in a functionally active state.     

Purification, characterization, and western blot analysis of human GTPase-activating protein from native and recombinant sources

Human ras GTPase-activating protein (GAP) is a cytoplasmic factor that stimulates the GTPase activity of normal N-ras p21 while having no stimulatory effect on the GTPase activity of oncogenic variants of N-ras p21. We have purified two forms of native ras GAP from human placental tissue. In addition to the Mr = 120,000 type I GAP reported previously (1), an equivalent amount of an Mr = 95,000 molecule with GAP activity was recovered and shown to have the N-terminal sequence expected for type II GAP. The two GAP forms in placental extracts were resolved by molecular sieve chromatography and appeared to have a monomeric native structure. Human recombinant type I GAP was produced intracellularly in Sf9 insect cells using a baculovirus expression vector, and 10-mg quantities were purified to homogeneity in three steps. Comparison of the purified native and recombinant GAP molecules revealed that all three displayed similar biological specific activities in an in vitro GAP assay. A polyclonal antibody to purified recombinant GAP was prepared and shown to neutralize the activity of both native and recombinant GAPs. The antibody was also highly specific for the detection of native GAP by Western blot. Type I and II GAP species were detected in approximately equal amounts in cytoplasmic extracts of human placenta, but only type I GAP was observed when other human tissues were examined.     

Fetal calf ligament fibroblasts in culture secrete a low molecular weight collagen with a unique resistance to proteolytic degradation

A highly unusual collagen was secreted by fibroblasts cultured from 150- and 270-d-old fetal calf nuchal ligaments. Purification revealed that this protein (which may be synthesized in a higher molecular weight form) was precipitated at unusually high concentrations of ammonium sulfate and was also eluted from DEAE-cellulose at greater salt concentrations than were types I and III procollagens. On SDS PAGE, the collagenous protein exhibited an Mr of approximately 12,750 that was not altered in the presence of reducing agent. The low molecular weight collagen (FCL-1) was sensitive to bacterial collagenase and had a [3H]glycine content comparable to that found in type I procollagen, although the [3H]Hyp to [3H]Pro ratio was 0.43. FCL-1 was not cleaved by human skin collagenase, mast cell protease, trypsin, Staphylococcal V8 protease, or proteinase K at 37 degrees C. The collagen was susceptible to trypsin, but not to V8 protease, only after heating at 80 degrees C for 30 min. Preliminary structural studies indicate that FCL-1 was resistant to cleavage by CNBr but exhibited limited proteolysis with pepsin. Both 150- and 270-d-old fibroblasts produced comparable levels of interstitial (types I and III) procollagens, which comprised approximately 70% of the total protein secreted into the culture medium. However, 270-d-old (term) fibroblasts secreted approximately 50% more FCL-1, as percent of total culture medium protein, in comparison to the cells from the earlier gestational stage. This collagen may therefore play a role in the development of the nuchal ligament.     

Further studies on calf thymus DNA polymerase delta purified to homogeneity by a new procedure

DNA polymerase delta from calf thymus has been purified to apparent homogeneity by a new procedure which utilizes hydrophobic interaction chromatography with phenyl-Sepharose at an early step to separate most of the calcium-dependent protease activity from DNA polymerase delta and alpha. The purified enzyme migrates as a single protein band on polyacrylamide gel electrophoresis under nondenaturing conditions. The sedimentation coefficient of the enzyme is 7.9 S, and the Stokes radius is 53 A. A molecular weight of 173K has been calculated for the native enzyme. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the homogeneous enzyme reveals two polypeptides of 125 and 48 kDa. This subunit structure differs from that of DNA polymerase delta prepared by our previous procedure, which was composed of subunits of 60 and 49 kDa [Lee, M. Y. W. T., Tan, C.-K., Downey , K. M., & So, A. G. (1981) Prog . Nucleic Acid Res. Mol. Biol. 26, 83-96], suggesting that the 60-kDa polypeptide may have been derived from the 125-kDa polypeptide during enzyme purification, possibly as the result of cleavage of an unusually sensitive peptide bond. DNA polymerase delta is separated from DNA polymerase alpha by hydrophobic interaction chromatography on phenyl-Sepharose; DNA polymerase delta is eluted at pH 7.2 and DNA polymerase alpha at pH 8.5. DNA polymerase delta can also be separated from DNA polymerase alpha by chromatography on hydroxylapatite; DNA polymerase alpha binds to hydroxylapatite in the presence of 0.5 M KCl, whereas DNA polymerase delta is eluted at 90 mM KCl.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative study of glucosidases from the thermophilic fungus Thermoascus aurantiacus Miehe. Purification and characterization of intracellular beta-glucosidase

Intracellular beta-glucosidase was extracted from the mycelium of Th. aurantiacus, concentrated by DEAE-cellulose treatment, separated from alpha-glucosidase by hydroxylapatite chromatography and purified to electrophoretic homogeneity. Optimally active at 75 degrees C and pH 4.2, beta-glucosidase displayed complex kinetics with p-nitrophenyl-beta-glucoside which inhibited the enzyme at concentrations greater than 0.5 mM. With cellobiose the kinetics were practically hyperbolic at 70 degrees C (Hill coefficient nH = 1.09 and Km = 0.83 mM), but faint inhibition was observed at 50 degrees C. beta-glucosidase shares with alpha-glucosidase a high number of physicochemical properties: with similar aminoacid composition, very close isoelectric point (4.5 and 4.2), high molecular weight in the native state (175,000 and 140,000), the two enzymes showed the same behaviour on DEAE-cellulose, were equally stable at high temperature and were dissociated by 6 M urea to still active proteins. Furthermore, the carbohydrate contents of beta-glucosidase (17.6%) is not far from that previously determined for some forms of alpha-glucosidase (14-16%).