Inhibition by polyamines of lipid peroxide formation in rat liver microsomes.

Both NADPH- and ascorbic acid-dependent lipid peroxidations were inhibited by spermine, the degree of inhibition being greater with the former peroxidation. The effective concentration of spermine required for inhibition was higher when larger amounts of microsomes were used. However, the activities of NADPH-cytochrome c reductase and NADPH-peroxidase were not influenced by spermine. These results suggest that spermine inhibits lipid peroxidation by binding to phospholipids in the microsomes.     

Comparative studies on the increase by polyamines of fidelity of protein synthesis in Escherichia coli and wheat germ cell-free systems.

In the presence of polyamines, the fidelity of protein synthesis in a wheat germ cell-free system was increased significantly, while it was increased slightly in an $\text{E. coli}$ cell-free system. The effective concentration of polyamines for the increase in fidelity of protein synthesis was nearly equal to that for the stimulation of protein synthesis in a wheat germ cell-free system.     

Studies on rat liver argininosuccinate synthetase. Inhibition by various amino acids.

Inhibition studies of crystallized rat liver argininosuccinate synthetase [EC 6.3.4.5] are described. 1. L-Argininosuccinate, L-histidine, and L-tryptophan inhibited the enzyme activity at saturating amounts of the substrates. 2. L-Norvaline, L-argininosuccinate, L-arginine, L-isoleucine, and L-valine competitively inhibited the enzyme activity at a low concentration of L-citrulline, with Ki values of 1.3 x 10(4) M, 2.5 X 10(-4) M, 6.7 X 10(-4) M, 6.3 X 10(-4) M, and 6.0 x 10(-4) M, respectively. 3. L-Argininosuccinate and L-arginine competitively inhibited the enzyme activity at a low concentration of L-aspartate, with Ki values of 9.5 x 10(-4) M and 1.2 x 10(-3) M, respectively. 4. The modes of inhibition by L-histidine were mixed-noncompetitive, uncompetitive, and noncompetitive types with respect to L-citrulline, L-aspartate, and ATP, respectively. 5. When the enzyme was preincubated with L-citrulline, the enzyme activity was slightly increased in the presence of a low concentration of L-histidine in the assay mixture. 6. The conformation of the enzyme was markedly changed by the addition of L-histidine as judged from the CD spectrum. This change was partially reversed by incubation with L-citrulline.     

Neutralization tests for dengue and Japanese encephalitis viruses by the focus reduction method using peroxidase-anti-peroxidase staining.

Neutralization tests were made on 4 types of dengue (DEN) virus and Japanese encephalitis (JE) virus by incubation of serially diluted antisera and constant amounts of the viruses and then focus assay of surviving virus infectivity with peroxidase-anti-peroxidase (PAP) staining. Neutralization reactions were virtually completed in 2 hr on incubation of serum-virus mixtures at 28 C. A straight regression line was obtained on a probit chart by plotting the focus reduction rates at various dilutions of a given serum against the logarithm of the serum dilution used in the test. The slopes of the probit regression lines for the neutralization for DEN types 1 and 3 were similar, but differed somewhat from those for DEN type 2 and type 4. The slope of the line for JE virus was quite different from those for DEN viruses. Using these relations, the fifty percent focus reduction titer (FR50) of neutralizing antibodies of a given serum could be estimated from the focus reduction rates at several dilutions of the test serum when the latter was between 25-75% of the value of the control.     

Polyamine prevention of inhibition of rat liver isoleucyl-tRNA formation by poly(G), poly(I) or ribosomes.

It is shown that rat liver isoleucyl-tRNA formation in the presence of Mg²⁺ is inhibited by poly(G), poly(I) or ribosomes and that this inhibition is prevented by polyamines. The inhibition is found to be noncompetitive with respect to tRNA.     

Change of substrate specificity by polyamines of ribonucleases which hydrolyze ribonucleic acid at linkages attached to pyrimidine nucleotides.

The activities of ribonucleases (RNase HS and RNase A), which hydrolyze ribonucleic acid at linkages attached to pyrimidine nucleotides were stimulated by polyamines, while the activities of ribonucleases (RNase T₁ and RNase M), which attack ribonucleic acid at linkages attached to purine nucleotides were not influenced by polyamines. In the presence of polyamines, the cleavage of C_5′-O-P linkages adjacent to cytosine nucleotide was stimulated, while the cleavage of C_5′-O-P linkages adjacent to uracil nucleotides was inhibited slightly. The effect of polyamines on the activities of ribonucleases occured through the binding of the polyamines to nucleic acid.     

Notes on some plant-inhabiting fungi collected from the Nansei Islands (2)

In this paper, four fungi collected in Nansei Islands are reported. One is Strasseria garciniae, which must be transferred to the genus Phyllosticta. This fungus was collected in Okinawa Main Island and Iriomote Island. The other three fungi are newly added to the Japanese fungal flora. Phyllosticta ghaesembillae on Codiaeum variegatum and Cercospora asplenii on Asplenium antiquum were collected in Yoron Island. The last one, Coniella australiensis on Eucalyptus robusta was collected in Okinawa Main Island. Their morphology and symptoms on the host plant are described, with some mycological notes.     

Enzymatic synthesis of N,N-dimethyl-sphingosine: demonstration of the sphingosine: N-methyltransferase in mouse brain

Based on our recent finding that N,N-dimethyl-D-erythro-sphingenine strongly inhibits protein kinase C (PK-C) whereas D-erythro-sphingenine produces only weak inhibition, we have studied the presence of N-methyltransferase responsible for conversion of sphingosine to its N,N-dimethyl derivative. The enzyme activity was detected in crude mouse brain tissue homogenate but was hardly detectable in liver homogenate, in which N-methylation of phosphatidylethanolamine (PE) is predominant.     

The tyrosine kinase v-Src modifies cytotoxicities of anticancer drugs targeting cell division

v-Src oncogene causes cell transformation through its strong tyrosine kinase activity. We have revealed that v-Src-mediated cell transformation occurs at a low frequency and it is attributed to mitotic abnormalities-mediated chromosome instability. v-Src directly phosphorylates Tyr-15 of cyclin-dependent kinase 1 (CDK1), thereby causing mitotic slippage and reduction in Eg5 inhibitor cytotoxicity. However, it is not clear whether v-Src modifies cytotoxicities of the other anticancer drugs targeting cell division. In this study, we found that v-Src restores cancer cell viability reduced by various microtubule-targeting agents (MTAs), although v-Src does not alter cytotoxicity of DNA-damaging anticancer drugs. v-Src causes mitotic slippage of MTAs-treated cells, consequently generating proliferating tetraploid cells. We further demonstrate that v-Src also restores cell viability reduced by a polo-like kinase 1 (PLK1) inhibitor. Interestingly, treatment with Aurora kinase inhibitor strongly induces cell death when cells express v-Src. These results suggest that the v-Src modifies cytotoxicities of anticancer drugs targeting cell division. Highly activated Src-induced resistance to MTAs through mitotic slippage might have a risk to enhance the malignancy of cancer cells through the increase in chromosome instability upon chemotherapy using MTAs.