Inhibition of Escherichia coli DNA polymerase-I by the anti-cancer drug cis-diaminedichloroplatinum(II): what roles do polymerases play in cis-platin-induced cytotoxicity?

Activities of Escherichia coli DNA polymerase-I were examined in the presence of the anti-tumor drug cis-diaminedichloroplatinum(II) and its inactive geometric isomer trans-diaminedichloroplatinum(II). The trans-isomer did not inhibit the enzyme activity. The anti-tumor drug, on the other hand, retarded the enzyme in its ability to extend the primer strand of DNA. Two alternative mechanisms of inhibition, covalent binding of cis-diaminedichloroplatinum(II) to the polymerase and to the template DNA, were explored. Selective preincubations of the platinum drug with the polymerase and DNA reveal that the inhibition is primarily due to covalent binding to the enzyme. The rates of inhibition were found to be first order in enzyme and zeroth order in platinum in the concentration range 0.05-3.0 mM. A mechanism that deals with the formation of an initial platinum-polymerase-I complex with a binding constant > 10(5) M(-1) followed by a further reaction to form an inhibitory complex is consistent with the kinetic data. The rate limiting first order rate constant for the formation of the inhibitory complex is comparable to that observed for the thiol coordination of peptides containing cysteine residues. Analyses of known structures and functions of catalytic domains of various polymerases point to the direction that the inhibition is perhaps due to the distortion of the DNA binding domain of the enzyme due to platinum coordination.     

Amphiphilic cationic peptides mediate cell adhesion to plastic surfaces

Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion.     

Modulating effect of cerulein on benzodiazepine receptors

Subcutaneous administration of caerulein (100-500 micrograms/kg) significantly reduced the development of picrotoxin (8 mg/kg) seizures in male mice. The same doses of caerulein inhibited 3H-flunitrazepam binding in in vivo experiments. Proglumide, an antagonist of cholecystokinin receptors, in low dose (5 mg/kg) potentiated the effects of caerulein (100 micrograms/kg), whereas the administration of proglumide in high dose (25 mg/kg) reduced the action of caerulein on 3H-flunitrazepam binding and picrotoxin seizures. Caerulein (5-1000 nM) decreased 3H-flunitrazepam binding in in vitro experiments only after supplementation of the binding medium with 120 mM NaCl and 5mM KCl. The results suggest the possible interaction of caerulein with chloride ionophor. It seems probable that the direct interaction of caerulein with chloride ionophor in involved in the inhibitory effect of caerulein on picrotoxin seizures and 3H-flunitrazepam binding.     

Analogs of oxytocin containing a modified peptide bond

Analogs of deamino-oxytocin and deamino-oxypressin containing a CH2-NH group instead of an amide bond between positions 8 and 9 were synthesized. All tested compounds exhibit significantly lowered biological activities.     

Purification and properties of thyrotrophin releasing hormone (TRH)-containing particles from the rat hypothalamus

The subcellular distribution of the TRH-like immunoreactivity in the rat hypothalamus and brain was studied. In differential centrifugation, the 900 g for 10 min supernatant (S1) of the hypothalamus or brain contained 61--79% of the total TRH. At 11,000 g for 20 min, 51--73% of the TRH in S1 was sedimented. When the hypothalamic S1 was fractioned under non-equilibrium conditions at 25 degrees C, two populations of TRH-containing particles were observed in several types of continuous linear density gradients. Metrizamide and sucrose gradients affected TRH-assay. TRH-particles were very light in Percol-gradients. Isotonic dextran 40,000-sucrose gradients gave the most reproducible results. In these gradients, the large TRH-particles (35%) equilibrated at 1.055--1.060 kg/l and the small ones (23%) at 1.041--1.047 kg/l. Working at 4 degrees C decreased the amount of large TRH-particles. The apparently larger particles contained cytoplasmic and mitochondrial enzymes and were sensitive to hypoosmotic shock like synaptosomes. Electron micrographs confirmed that these particles were synaptosomes. The true nature of the small particles remained unclear but morphologically a part of them were also synaptosomes. Treatment of the animals with reserpine (10 mg/kg i.p., 24 h), with 6-hydroxydopamine (100 microgram/rat i.c.v.) or with 5,7-dihydroxytryptamine (200 microgram/rat i.c.v.) did not affect significantly TRH-recovery or distribution in the hypothalamus.     

Syngeneic anti-idiotypic antisera to murine monoclonal antibodies to monomorphic and polymorphic determinants of HLA class I antigens

BALB/c mice were immunized with syngeneic anti-HLA class I monoclonal antibodies. The latter included the anti-HLA-A2, A28 monoclonal antibody (MoAb) CR11-351, the MoAb Q6/64 to a determinant restricted to HLA-B antigens and the MoAb CR10-215 and CR11-115 to the same (or spatially close) monomorphic determinant. Anti-idiotypic antibodies could be detected in bleedings obtained 3 days after the first booster, increased in titer in bleedings obtained after the second booster, and persisted at high levels in subsequent bleedings. The four anti-HLA class I MoAb did not differ in their ability to elicit syngeneic anti-idiotypic antibodies. Cross-blocking studies with a panel of anti-HLA class I, anti-HLA class II, and anti-human melanoma-associated antigen (MAA) MoAb showed that the anti-MoAb CR10-215 and anti-MoAb CR11-115 antisera contain only antibodies to private idiotopes, whereas the anti-HLA MoAb CR11-351 and anti-MoAb Q6/64 antisera also contain antibodies to public idiotopes. The latter are expressed by the anti-HLA class I MoAb CR11-351, Q1/28, Q6/64, and 6/31, and by the anti-HLA class II MoAb Q5/6, Q5/13, 127, and 441. Public idiotopes were not detected on the nine anti-MAA MoAb tested. Public idiotopes do not interfere with the binding of anti-HLA MoAb with the corresponding antigenic determinants. On the other hand private idiotopes are located within the antigen-combining site, because anti-idiotypic antisera specifically inhibit the binding of the corresponding immunizing anti-HLA class I MoAb to cultured human lymphoid cells in a dose-dependent manner. Analysis by isoelectric focusing of the anti-HLA class I MoAb antisera showed that the spectrotype of the anti-MoAb CR11-351 antiserum comprises four components that focus in the pH 6.9 to 6.2 range, the spectrotype of anti-MoAb Q6/64 antiserum comprises three components that focus in the pH 6.5 to 6.1 range, the spectrotype of the anti-MoAb CR10-215 antiserum comprises three components that focus in the pH 6.4 to 6.1 range, and the spectrotype of the anti-MoAb CR11-115 antiserum comprises three components that focus in the pH 6.6 to 6.4 range.     

Structure of the lysosomal sphingolipid activator protein 1 by homology with influenza virus neuraminidase

The sphingolipid activator protein 1 (SAP-1) increases the rate of hydrolysis of sphingolipids in the lysosome by apparently bringing together the substrate and the corresponding hydrolytic enzyme. This implies specific recognition of both the substrate and enzyme by SAP-1. However, binding domains in SAP-1 and recognition mechanisms involved are unknown. Amino acid sequence comparison of SAP-1 with influenza virus neuraminidase (EC 3.2.1.18, FLU NA) indicates that functional amino acid residues in or near the sialic acid binding site of FLU NA are also found at equivalent positions in the first 48 N-terminal amino acids of SAP-1. This region of homology allows to propose folding of the SAP-1 polypeptide chain by comparison with known crystallographic structure of FLU NA and identify a potential domain for lysosomal enzyme recognition through sialic acid binding. There is also a region of 10 amino acid residues near the C-terminal end of SAP-1 which has a strong propensity to form an alpha-helix with amphiphilic properties of lipid-binding helices. This domain in SAP-1 is probably responsible for the lipid(substrate)-binding function of SAP-1.