Functional cysteinyl residues in human placental aldose reductase

Incubation of human placental aldose reductase (EC 1.1.1.21) with the sulfhydryl oxidizing reagents 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) and N-ethylmaleimide (NEM) results in a biexponential loss of catalytic activity. Inactivation by DTNB or NEM is prevented by saturating concentrations of NADPH. ATP-ribose offers partial protection against inactivation by DTNB, whereas NADP, nicotinamide mononucleotide (NMN), and the substrates glyceraldehyde and glucose offer little or no protection. The inactivation by DTNB was reversed by dithiothreitol and partially by 2-mercaptoethanol but not by KCN. When the release of 2-nitro-5-mercaptobenzoic acid was measured, 3 mol of sulfhydryl residues was found to be modified per mole of the enzyme by DTNB. Correlation of the fractional activity remaining with the extent of modification by the statistical method of C.-L. Tsou (1962, Sci. Sin. 11, 1535-1558) indicates that of the three reactive residues, one reacts at a faster rate than the other two, and that two residues are essential for the catalytic activity of the enzyme. Labeling of the total sulfhydryl by [14C]NEM and quantification of DTNB-reactive residues in the enzyme denatured by 6 M urea indicates that a total of seven sulfhydryl residues are present in the protein. The modification of the enzyme did not affect Km glyceraldehyde, but the modified enzyme had a lower Km NADPH. Kinetic analysis of the data suggests that a biexponential nature of inactivation could be due to the formation of a dissociable E:DTNB complex and the presence of a partially active enzyme species.     

Selectivity of modification when latent and activated forms of the chloroplast F1-ATPase are inactivated by 7-chloro-4-nitrobenzofurazan

The characteristics and specificity of inactivation of the chloroplast F1-ATPase (CF1) with 7-chloro-4-nitrobenzofurazan (Nbf-Cl) have been investigated. Inactivation of the octylglucoside-dependent Mg2+-ATPase activity of latent CF1 by Nbf-Cl can be correlated with the formation of about 1.2 mol of Nbf-O-Tyr per mole of enzyme. Following inactivation of CF1 with [14C]Nbf-Cl, polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed that the majority of the radioactive reagent incorporated is present in the beta subunit. Treatment of the enzyme with [14C]Nbf-Cl following dithiothreitol heat activation, led to similar labeling of the beta subunit and substantial incorporation of 14C into the gamma subunit. On complete inactivation, about 4 mol of Nbf-S-Cys is formed per mole of dithiothreitol-heat-activated CF1. Incorporation of 14C into the gamma subunit is prevented by prior treatment of the latent CF1 or of the dithiothreitol-heat-activated CF1 with iodoacetamide. Following incubation of the dithiothreitol-heat-activated CF1 with iodoacetamide, complete inactivation of the octylglucoside-dependent Mg2+-ATPase activity by Nbf-Cl can be correlated with the formation of about 1.2 mol of Nbf-O-Tyr per mole of enzyme. After stabilization of the [14C]Nbf-O-Tyr derivative by treatment with sodium dithionite, a labeled peptide was purified. Automatic Edman degradation of this peptide revealed the sequence V-X-V-P-A-D-(D). The majority of the radioactivity was cleaved in the second cycle, the position occupied in CF1 by Tyr-beta-328, which is homologous to Tyr-beta-311, the residue reactive with Nbf-Cl in the beef heart mitochondrial F1-ATPase. When CF1, modified at Tyr-beta-328 with Nbf-Cl, is incubated at pH 9.0, the Nbf-O-Tyr adduct is hydrolyzed, leading to concomitant recovery of the ATPase activity. In double labeling experiments, two-dimensional isoelectric focusing in the presence of urea followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicates that 2-azido-ADP, covalently bound at the tight ADP binding site, and the tyrosine modified by [14C]Nbf-Cl are located in different beta subunits.     

Intracellular protein phosphorylation in oat (Avena sativa L.) protoplasts by phytochrome action. 1. Measurement of action spectra for the protein phosphorylation

The effects of red light and wavelength dependency of the protein phosphorylation in oat protoplasts were investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography. Red light (660 nm) irradiation of the protoplasts increased the phosphorylation of 15 different proteins, and the phosphorylation of 2 proteins (27 KDa, 32 KDa) out of 15 were observed to be dependent on the wavelength of the irradiating light. The phosphorylation densities of these two proteins increased up to two or three hundred percent during a three-minute period of irradiation. The phosphorylation of these two proteins revealed a red/far-red photoreversibility of phytochrome. When a calcium ion chelator (2 mM EGTA) was added into the cell suspension, the phosphorylations of all the proteins were reduced about 200%. These findings suggest that phytochrome action and Ca2+ influx are certainly involved in the in vivo phosphorylation of proteins in oat protoplasts.     

Multiple forms of SppI (secreted phosphoprotein, osteopontin) synthesized by normal and transformed rat bone cell populations: regulation by TGF-beta

Metabolic labeling has revealed that rat bone cell populations in culture synthesize several forms of the secreted phosphoprotein, SppI. Most cell populations produced two major [32PO4]-labeled forms that behaved anomolously on SDS-PAGE migrating at 60 kDa and 56 kDa on 10% gels and 55 kDa and 44 kDa on 15% gels. Minor forms of intermediate sizes were also resolved. In normal bone cells the 60 kDa form was predominant and was the only form produced by the clonal bone cell line, RCA 11, whereas the 56 kDa a form predominated in the transformed bone cell line, ROS 17/2.8. In all populations [35S]-methionine-labeling revealed SppIs at approximately 60 kDa but no 56 kDa form. Each form of SppI was specifically cleaved by thrombin which generated fragments of approximately 28 kDa. Transforming growth factor beta 1 increased SppI mRNA levels 3 to 6-fold within 24 h in the normal bone cells, but no increase occurred in the ROS 17/2.8 cells. The elevated expression of SppI was reflected in a selective increase in the synthesis of the [32PO4]-and [35S]-methionine-labeled 60 kDa SppIs.     

Tyrosine phosphorylation in human neutrophil

Protein tyrosine phosphorylation in human neutrophils was examined by immunoblotting with antibodies specific for phosphotyrosine. The addition of the human hormone granulocyte-macrophage colony stimulating factor to human neutrophils caused an increase in the tyrosine phosphorylation levels of several proteins. The increases in at least two of these proteins having molecular masses of 40 kDa (p40) and 54 kDa (p54) were rapid and were inhibited in pertussis toxin treated cells. The newly synthesized tyrosine kinase inhibitor ST 638 inhibited the increases in the levels of the tyrosine phosphorylation in p92, p78, p54 and p40 proteins. The epidermal growth factor receptor tyrosine kinase inhibitors were less effective. The addition of the chemotactic factor fMet-Leu-Phe to human neutrophils also caused an increase in tyrosine phosphorylation in some of these proteins. The pattern of the fMet-Leu-Phe-induced tyrosine phosphorylation was different from that produced by GM-CSF. The increases were also inhibited by ST 638. In addition, ST 638 inhibited superoxide production but not actin polymerization in control and GM-CSF-treated cells stimulated with fMet-Leu-Phe. Moreover, the active but not inactive phorbol esters increase the tyrosine phosphorylation only in the 40 kDa protein. These results suggest several points: (a) some of the responses produced by GM-CSF and fMet-Leu-Phe are mediated through tyrosine phosphorylation, (b) the GM-CSF receptor is coupled to a pertussis toxin sensitive G-protein, (c) the 40 kDa protein is probably the Gi alpha 2, and (d) the 78 or the 92 kDa protein is most likely the receptor for GM-CSF, which indicates that the receptor may have a tyrosine kinase domain.     

A new compound, withangulatin A, promotes type II DNA topoisomerase-mediated DNA damage

Withangulatin A, a new compound with a known chemical structure and from the antitumor Chinese herb Physalis angulata L, was found to act on topoisomerase II to induce topoisomerase II-mediated DNA damage in vitro. It has two effective dosage ranges of approximate 0.5 and 20 microM, with about one-third the activity of 20 microM VM-26.     

Highly efficient DNA delivery mediated by pH-sensitive immunoliposomes

We have previously shown that pH-sensitive immunoliposomes can mediate a target-specific delivery of plasmid DNA to tumor cells grown in a mouse model [Wang, C.-Y., & Huang, L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 7851-7855]. The efficiency of delivery in terms of the target cell transformation frequency has now been characterized for both short- and long-term gene expression in a tissue culture system. Herpes simplex virus thymidine kinase (TK) gene was used as a reporter gene. It was placed under the control of the promoter for the rat phosphoenolpyruvate carboxykinase gene, which contains a cAMP regulatory element. Therefore, the expression of the exogenous gene in the target cell, mouse Ltk- cells, can be regulated by cAMP drugs. The plasmid DNA was encapsulated in liposomes using a detergent dialysis method. The efficiency of gene delivery was optimized with respect to the time course and dose of liposome-associated DNA. The existence of antibody of the liposomes was essential for the maximal level of DNA delivery. Delivery was also dependent on the lipid composition of the liposome. The pH-sensitive lipid composition gave 8-fold higher efficiency than the corresponding pH-insensitive composition. The transformation efficiency of the target cell also depended on the regulation of gene expression; cells incubated with dibutyryl-cAMP and theophylline showed a much higher level of transformation frequency than cells incubated without the drugs. When all liposome and incubation parameters are optimized, the Ltk- cells showed a 47% efficiency for the short-term transformation, and 2% for the long-term transformation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Levels of protein kinase C activity in human gastrointestinal cancers

The protein kinase C (PKC) activities of tumor tissue and adjacent normal mucosa of human cancers of the esophagus (8 cases), stomach (1 case) and colon (3 cases) were measured. Considerable variations were found in the activity of PKC and in its subcellular distribution in these cancers. The PKC activities of the membrane and cytosolic fractions of the eight esophageal cancers were, however, similar to those of the adjacent normal mucosa: the average PKC activities of the tumor tissues and normal mucosa were 7.5 and 8.3 pmol/min/mg protein, respectively, in their membrane fractions and 7.9 and 7.8 pmol/min/mg protein, respectively, in their cytosolic fractions.     

Trigramin: primary structure and its inhibition of von Willebrand factor binding to glycoprotein IIb/IIIa complex on human platelets

Trigramin, a naturally occurring peptide purified from Trimeresurus gramineus (T. stejnegeri formosensis) snake venom, inhibits platelet aggregation and the binding of 125I-fibrinogen to ADP-stimulated platelets (Ki = 2 X 10(-8) M) without affecting the platelet-release reaction. 125I-trigramin binds to ADP-stimulated and to chymotrypsin-treated normal platelets but not to thrombasthenic platelets. 125I-trigramin binding to platelets is blocked by monoclonal antibodies directed against the glycoprotein IIb/IIIa complex and by Arg-Gly-Asp-Ser (RGDS) [Huang et al. (1987) J. Biol. Chem. 262, 161]. We determined the primary structure of trigramin, which is composed of a single polypeptide chain of 72 amino acid residues and six disulfide bridges. The molecular weight of trigramin calculated on the basis of amino acid sequence was 7500, and the average pI was 5.61. An RGD sequence appeared in the carboxy-terminal domain of trigramin. An amino-terminal fragment (7-33) of trigramin showed 39% homology with a region (1555-1581) of von Willebrand factor (vWF). Trigramin also showed 36% identity in a 42 amino acid overlap and 53% identity in a 15 amino acid overlap when compared with two adhesive proteins, collagen alpha 1 (I) and laminin B1, respectively. Trigramin blocked binding of human vWF to the glycoprotein IIb/IIIa complex in thrombin-activated platelets in a dose-dependent manner. Reduction of trigramin resulted in a marked decrease in its ability to block vWF binding to human platelets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fetal lamb 3 beta, 20 alpha-hydroxysteroid oxidoreductase: dual activity at the same active site examined by affinity labeling with 16 alpha-(bromo[2'-14C]acetoxy)progesterone

3 beta,20 alpha-Hydroxysteroid oxidoreductase was purified to homogeneity from fetal lamb erythrocytes. The Mr 35,000 enzyme utilizes NADPH and reduces progesterone to 4-pregnen-20 alpha-ol-3-one [Km = 30.8 microM and Vmax = 0.7 nmol min-1 (nmol of enzyme)-1] and 5 alpha-dihydrotestosterone to 5 alpha-androstane-3 beta, 17 beta-diol [Km = 74 microM and Vmax = 1.3 nmol min-1 (nmol of enzyme)-1]. 5 alpha-Dihydrotestosterone competitively inhibits (Ki = 102 microM) 20 alpha-reductase activity, suggesting that both substrates may be reduced at the same active site. 16 alpha-(Bromoacetoxy)progesterone competitively inhibits 3 beta- and 20 alpha-reductase activities and also causes time-dependent and irreversible losses of both 3 beta-reductase and 20 alpha-reductase activities with the same pseudo-first order kinetic t1/2 value of 75 min. Progesterone and 5 alpha-dihydrotestosterone protect the enzyme against loss of the two reductase activities presumably by competing with the affinity alkylating steroid for the active site of 3 beta,20 alpha-hydroxysteroid oxidoreductase. 16 alpha-(Bromo[2'-14C]acetoxy) progesterone radiolabels the active site of 3 beta,20 alpha-hydroxysteroid oxidoreductase wherein 1 mol of steroid completely inactivates 1 mol of enzyme with complete loss of both reductase activities. Hydrolysis of the 14C-labeled enzyme with 6 N HCl at 110 degrees C and analysis of the amino acid hydrolysate identified predominantly N pi-(carboxy[2'-14C]methyl)histidine [His(pi-CM)].(ABSTRACT TRUNCATED AT 250 WORDS)