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- Biochemie und Chemie (7) (remove)
Some physical and chemical properties of the cancerostat cyclophosphamide (generic name: ENDOXAN) and its basic constituents H3PO4 and nor-N-mustard have been calculated with the help of a modified CNDO/S-method. The spectroscopic data of the H3PO4 , which is the starting-point for a corresponding calculation of cyclophosphamide, has been studied by taking account of the 3 d electron of the phosphorus. Nor-N-mustard is a very reactive compound, characterized by the ability to split off chloride ions and to act as an alkylating agent. The binding of the nor-N-mustard to the cyclic phosphate ester (cyclophosphamide) modifies the chemical reactivity of the mustard group in an essential way, and the 3d electron of the phosphorus plays an important role with respect to the excitability of the C -Cl bonds. Cyclophosphamide must be metabolized in a suitable way to develop the same alkylating activity as the nor-N-mustard. The computation of the excited states of cyclophosphamide revealed a similar term scheme as it was found by Clar in the case of the carcinogenic polycyclic hydrocarbons.
The kinetically stable triazatriphosphorinyl and tetraazatetra-phosphorocinyl azides 3 and 4 are prepared from the corresponding chlorides 1, 2 with sodium azide. 3 and 4 react with phosphanes to yield the λ5 -diphosphazenes 5a-d. By the reaction of 1 or 2 with KCN the nitriles 6 and 7 are formed. -The new compounds are characterized on the basis of IR and mass spectra.
The sequence complexity of nuclear RNA from mouse liver, mouse spleen and highly malignant P815 mastocytoma was measured by nRNA driven hybridization to unique DNA sequences of P815 cells. The unique DNA sequences represent 63% of the total nuclear DNA of P815 cells and their availibility in hybridization experiments was found to be 76%. Of these sequences 7.8% formed hybrids with nuclear RNA of this cell, about 11.5% with mouse spleen and about 14.5% with mouse liver nuclear RNA. Assuming an asymmetrical transcription, the complexities of these transcripts are 2.8 × 108 nucleotides for mouse P815 mastocytoma, 4.3 × 108 for mouse spleen and about 5.3 × 108 nucleotides for mouse liver.
Cellular specifity of the transcribed information was analyzed in additivity experiments, in which unique DNA sequences, not complementary to the nuclear RNA of one cell were annealed to the nuclear RNAs of the two other tissues/cells. In these experiments most of the nuclear RNA se quences of P815 cells were found to be also present in the nucleus of mouse liver and spleen. Only a small portion of the unique DNA sequences of P815 mastocytoma (about 1.2% corresponding to 4.4 ×107 nucleotides) was found to be complementary only to P815 mastocytoma nuclear RNA.
3,17 β-Hydroxysteroid dehydrogenase has been enriched and purified from cytosol of Streptomyces hydrogenans. After ammonium sulfate precipitation and filtration on Sephadex G-100 the enzyme was finally purified by preparative gel electrophoresis and DEAE-Sephadex A-50 chromatography. Polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate gave a single band of mobility corresponding to molecular weight of 70 200 ± 2 500. 3 β-. 17 β- as well as 20 β-hydroxy steroids were dehydrogenated by the enzyme in the presence of NAD+. The dehydrogenation proceeded faster than the reduction of the corresponding ketosteroids in the presence of NADH. The enzyme does not accent NADP+ or NADPH as co-substrates. The apparent Km values were calculated to be 11 μᴍ for 5 α-dihydrotestosterone, 20 μᴍ for testosterone ana 68 μᴍ for epiandrosterone in the NAD+-driven reaction, 1.8 x 10-4 m for NADH+ and 1.9 x 10-4 ᴍ for NADH. The catalytic activity was influenced by the ratio of NAD+/ATP. The inhibition by ATP appears to be of a competitive type with respect to NAD+ (Ki 1.15 x 10-3 ᴍ).
After sucrose gradient centrifugation in a preparative ultracentrifuge the enzyme sediments with 4.1 ± 0.1 S as estimated in comparison to other proteins of known sedimentation coefficient. The isoelectric point was determined to be 3.9 with the LKB preparative isoelectric focusing column (pH 2-11) and 4.1 with the analytical flat bed polyacrylamide isofocusing (pH 3 - 5). The number of SH groups was determined to be 2 mol/mol enzyme. In the presence of 6 M urea the figure inceases to 3 mol SH/mol enzyme. In the presence of an excess of p-chloromercuribenzoate the enzyme activity decreases only partially.
The title compound N,N-bis(trimethylstannyl)trifluoromethanesulfonamide (1) reacts with S2Cl2, SOCl2 and SO2Cl2 in a molar ratio 2:1 to yield the compounds S2Cl2 a twelve-membered ring 6. These are the largest neutral sulfur-nitrogen rings of coordination number two at the sulfur atoms known to date. 3 reacts with SOCI2 under migration of a methyl group from the tin to a sulfur atom to yield CF3SO2(R3Sn)NS(CH3)NSO2CF3 (7). 2,2,4,4-Tetramethyl-1,3-bis(trifluormethylsulfonyl)cyclodisilazan and 7 are formed by the reaction of 3 with R2SiCl2- The analogous four-membered germanium compound 8 is obtained from 1 and R2GeCl2. While the pyrolysis of 1 yields only the six-membered cyclotristannazan 9, the six-membered germanium analog is only formed in minor amounts. By treating 9 with R3SiCl the ring is decomposed to give 10. A six-membered ring is formed from the reaction of 1 with ClR2SiOSiR2Cl 11. The structure of 6 is discussed in detail. 6 crystallizes in the monoclinic space group C2/c with a = 24.408(5), b = 7.377(2), c = 16.715(3) Å, β = 117.16(3)° and Z = 4. It has a chair conformation which is different from the isoelectronic S12-structure.
A specific class of DNA sequences, the inverted repetitive sequences, forms a double-stranded structure within a single linear polynucleotide chain in denatured DNA. The reassociation process is unimolecular and occurs very fast. Quantitative analyses have shown that these sequences com-E rise about 4-5% of the nuclear DNA of various mammalian cells (P815 mouse mastocytoma, Hela, L cells, Raji and Chang cells, and human embryonic hepatocytes) and are interspersed within sequences of other degrees of repetitiveness.
After labeling the cells with L-[Metnyl-3H]methionine and [14C]deoxycytidine, relative rates of enzymic DNA methylation were computed on the basis of 3H and 14C radioactivities found in py rimidine residues of the nuclear DNA. The results indicate that DNA of inverted repetitive sequences is methylated to a level about 50% higher than the ordinary repetitive sequences and to about 300% higher than the unique and intermediary sequences.
The biological function of the inverted repeats as well as the role of their enzymic hypermethyl ation is unknown.
The reactions of N,N′ -bis(pentafluorophenyl)sulfurdiimide with [(CH3)3Sn]2NCH3, [(CH3)3Sn]3N and [(CH3)3Sn]2NC6F5 yiels the 1:1 adducts 1-3. 1H and 19 F NMR investigations show, that fluorine atoms in the ortho position of the phenyl ring coordinate to the tin atom. This causes an increase of electron density at tin. A similar interpretation is given for the adduct 4 of N,N′-bis(p-chlorophenylsulfonyl)sulfurdiimide and [(CH3)3Sn]2NCH3, where an oxygen atom of the sulfonyl group is bonded to tin.