Zeitschrift fur Naturforschung. Section C, Biosciences最新文献

[14C]penicillin binding experiments and membrane analysis were carried out with cell envelope preparations from Escherichia coli and Proteus mirabilis. After incubation with [14C]penicillin G labeled free lipoprotein could be identified. The analysis of the isolated lipoprotein by SDS polyacrylamide gel electrophoresis indicates that there is only one protein with an apparent molecular weight of 7000. The amino acid composition of isolated labeled free lipoprotein from E. coli was identical to the lipoprotein already found in E. coli. It is a point of interest that the amino acid composition of the isolated labeled free lipoprotein from P. mirabilis D 52 differs from that found in other mutants of this strain. The free form of lipoprotein from P. mirabilis D 52 is composed of 61 amino acids and has glycine, phenylalanine and proline as specific components.

The effect of L-norleucine, an isomer of leucine, on protein metabolism in vivo was studied in suckling rats. Rats were injected subcutaneously with various doses of L-norleucine (0.5 and 5.0 mumol/g body wt.) every 12 h from 3 to 15 days post partum. Protein concentration, amino acid concentrations, and incorporation of [3H]tyrosine into protein were analyzed in liver, muscles of thigh and small intestine. Amino acid concentrations and insulin levels in serum were also measured. At 5 days of age, norleucine induced an increase in protein concentration of skeletal muscle with an increased incorporation of [3H]tyrosine into protein indicating an accelerated protein synthesis. Changes in protein metabolism were paralleled by alterations in the amino acid pattern of this tissue. When protein concentration and protein synthesis were increased in skeletal muscle, protein concentration of small intestine was decreased, accompanied by elevated levels of amino acids in tissue. Protein synthesis of small intestine was not altered by the norleucine treatment. The results suggest a close interrelationship between skeletal muscle and small intestine with respect to protein turnover. The effects of norleucine were less pronounced at 10 and 15 days of age, which indicates a metabolic adaptation to the treatment. Alterations in amino acid concentrations of tissue due to changes in protein metabolism were not uniform but tissue-specific. Current concepts for explaining the effects of branched-chain amino acids (BCAA) on protein turnover in skeletal muscle are based on the assumption that the BCAA or leucine alone might become rate-limiting for protein synthesis in muscle under catabolic conditions. The amino acid analogue norleucine, however, cannot replace any of the BCAA in protein. Additionally, norleucine affected protein metabolism in highly anabolic organisms. Therefore, the present thoughts on this issue appear to be incomplete.

Oxidation of methionine, 4-(methylthio)-2-oxobutyric acid (KMB), or 1-aminocyclopropane carbonic acid (ACC) are indicator reactions for activated oxygen species such as singlet oxygen (1O2), OH.-radical like oxidants, superoxide anion (O2.-), hydrogen peroxide (H2O2) or activated hemo-iron complexes like peroxidase- or catalase-"compound I". Methionine is oxidized by OH. as well as by 1O2 forming ethylene, but not by tetrachloro-decaoxygen complex (TCDO) in the absence or presence of catalytic hemoproteins such as peroxidase, hemoglobin or myoglobin. Both KMB and ACC are oxidized by TCDO under the catalysis of the above hemo-proteins where neither catalase nor superoxide dismutase are inhibitors. TCDO hemo-protein complex is an oxidant with similar properties as peroxidase-compound I and can clearly be differentiated from O2.-, H2O2, OH. and 1O2.

The fatty acyl specificity of phospholipase A1 and A2 in homogenates of mouse bone marrow-derived macrophages was determined using phosphatidylcholine and phosphatidylethanolamine of different acyl chain composition. Phosphatidylcholine with arachidonoyl at position 2 was cleaved preferentially by an alkaline phospholipase A2 (pH-optimum 9.0) leading to selective liberation of arachidonic acid. In contrast, phosphatidylcholines with oleoyl or linoleoyl at position 2 were degraded mainly by an acid phospholipase A1 (pH-optimum 4-5) resulting in a conservation of these fatty acids esterified in lysophosphatides. Substrate kinetics of the alkaline phospholipase A2 revealed a 30 fold higher affinity (Km = 3.8 X 10(-7) M) for 1-acyl-2-arachidonoyl-glycerophosphocholine compared to 1-acyl-2-oleoyl-glycerophosphocholine. The kinetic data were not influenced by endogenous lipids indicating that exogenous substrates do not equilibrate with cellular lipids. These results are suitable to explain a selective liberation of arachidonic acid from a mixture of phospholipids.

Chemiluminescence (CL) that appears during oxidation of lecithin and ascorbate has been studied. A simple system consisting only of purified lecithin, which has one double bond, and ascorbate as a physiological reductant with a low redox potential, was used. The CL spectrum of lecithin contain a strong band lying in the near infrared, and three bands at 20 900 cm-1, 17 700 cm-1 and 15 800 cm-1, being characteristic of singlet molecular oxygen (1O2). The effect of 1O2 quenchers on both autooxidation processes has also been investigated. The obtained results indicate that the main emitter is the 1O2. An addition of ascorbate to the system lecithin plus buffer causes a decrease of CL intensity. That is a result of stronger quenching properties of ascorbate and not due to efficiency of the generation of 1O2.

The rate constant for strand breakage in poly(U) after reaction with hydrogen atoms in deoxygenated aqueous solution has been determined to be k = 1.5 s-1 at pH = 4-5 and 24 degrees C. Dithiothreitol has been found to prevent strand break formation by reacting with H-adduct radicals of poly(U) with a rate constant of 5 X 10(6) M-1 s-1. It is concluded that the rate-determining step in H atom-induced strand breakage in poly(U) at pH less than or equal to 6 is the decay of uracil moiety H-adduct radicals via H-abstraction from the ribose moiety.

The amount of streptolysin S produced by resting streptococci was considerably increased after incubation of the washed bacteria with trypsin or pronase. Production of both cell-bound and free forms of the toxin was enhanced by the protease treatment. By addition of trypsin, streptolysin S yield was considerably increased in growing culture as well. Treatment with lysozyme was ineffective, and the toxin production was only slightly promoted by preincubation with hyaluronidase or chymotrypsin. In contrast, pretreatment with chymotrypsin caused increased production of an extracellular nuclease, whereas the yield of this enzyme was reduced after incubation of the cocci with pronase. Evidence was obtained indicating de novo synthesis of the exotoxin in the protease-treated bacteria.

Hydrogen atoms from the radiolysis of water at pH 1.6 add to the 5,6-double bond of pyrimidines. The preferential site of attack is the C(5) position (values in brackets) in the case of 6-methyluracil (87%), 1,3-dimethyluracil (71%), uracil (69%) and poly(U) (60%). This reaction yields a radical of reducing properties which can be monitored by its reaction with tetranitromethane in a pulse radiolysis experiment. In thymine (37%), thymidine (32%) and 1,3-dimethylthymine (25%) H-addition no longer preferentially occurs at C(5), but addition is now mainly at C(6). Hydrogen abstraction from the methyl groups or the sugar moiety is negligible (less than or equal to 5.5%). A comparison is made with literature values for the equivalent reactions of OH radicals.

The nucleotide sequence of the bovine 1.723 satellite DNA repeated unit was determined. The 680 bp long period of this satellite DNA does not show any significant sequence similarities with the known bovine satellite DNAs. Short repetitive sequences which are parts of 680 bp long repeated units do not form any orderly periodical structure. It seems, however, that the basic repeated unit of the 1.723 bovine satellite DNA has been formed by successive duplications of two, about 100 bp long sequences. The sequence divergence between different copies of the 680 bp repeated unit was also analyzed.

Monoclonal antibodies were raised against the lectin of Helix pomatia (HPL). Besides antibodies bearing the more common gamma and kappa chains, antibodies with alpha, mu and lambda 2 chains were elicited. The anti-HPL antibodies are expected to be useful in studies on HPL biogenesis and HPL substructure and in studies concerned with the binding of HPL to cell surfaces. Binding of carbohydrates to HPL impaired the binding of anti-HPL antibodies. One to 3 mM GalNAc inhibited HPL-binding in two out of nine antibodies. None of the antibodies bound in the presence of micrograms per ml of the polyvalent blood group A-substance from hog stomach. Similarly, all anti-HPL antibodies were prevented from binding if non-inhibitory concentrations of A-substance were supplemented with GalNAc. Lectins from Helix aspersa (HAL) and Helix lucorum (HLL) differed from HPL in antigenic properties. Only one anti-HPL antibody each bound these lectins as well as HPL. Binding of lectins of Cepaea and Rapana was scarcely detectable. Most of the anti-HPL antibodies and the multivalent HPL-antigens formed precipitation lines in double diffusion tests. At least two antibodies (IgMs) did so with HLL but none with HAL. The possibility that antibodies were selected because of unknown interactions between HPL and the carbohydrate moieties of certain fractions of antibodies was excluded by raising the antibodies in the presence of tunicamycin to inhibit N-glycosylation.