Relation between D-glucose and L- and D-alanine in the initiation of germination of Bacillus subtilis spore

The rate of L-alanine-initiated germination of Bacillus subtilis spore was measured by both loss of heat resistance and loss of turbidity, and the effect of glucose on the germination response to a wide range of concentrations of the germinant was analyzed in the presence and absence of D-alanine, an inhibitor. Glucose stimulated L-alanine germination by means of a cooperative effect: glucose increased the affinity of L-alanine by about 3-fold and the rate of germination by about 1.3-fold. However, glucose had little effect on the binding affinity of D-alanine. The apparent binding constant of L-alanine to the spore, which was determined by the next measurable event in the trigger reaction, was 1.2 X 10(-5), that of D-alanine was 6 X 10(-6), and that of glucose was 5 X 10(-5). The relation between the binding site for glucose and those for L- and D-alanine on the spore is discussed. Effect of glucose analogs was also examined.     

ATM regulates Cdt1 stability during the unperturbed S phase to prevent re-replication

Ataxia-telangiectasia mutated (ATM) plays crucial roles in DNA damage responses, especially with regard to DNA double-strand breaks (DSBs). However, it appears that ATM can be activated not only by DSB, but also by some changes in chromatin architecture, suggesting potential ATM function in cell cycle control. Here, we found that ATM is involved in timely degradation of Cdt1, a critical replication licensing factor, during the unperturbed S phase. At least in certain cell types, degradation of p27^Kip1 was also impaired by ATM inhibition. The novel ATM function for Cdt1 regulation was dependent on its kinase activity and NBS1. Indeed, we found that ATM is moderately phosphorylated at Ser1981 during the S phase. ATM silencing induced partial reduction in levels of Skp2, a component of SCF^Skp2 ubiquitin ligase that controls Cdt1 degradation. Furthermore, Skp2 silencing resulted in Cdt1 stabilization like ATM inhibition. In addition, as reported previously, ATM silencing partially prevented Akt phosphorylation at Ser473, indicative of its activation, and Akt inhibition led to modest stabilization of Cdt1. Therefore, the ATM-Akt-SCF^Skp2 pathway may partly contribute to the novel ATM function. Finally, ATM inhibition rendered cells hypersensitive to induction of re-replication, indicating importance for maintenance of genome stability.     

Analysis of the mode of antigen presentation required for triggering of T cell proliferation by using various azobenzenearsonate-tyrosine derivatives

Various azobenzenearsonate-tyrosine (ABA-Tyr) derivatives were synthesized by modifying amino and carboxyl groups at the alpha-carbon of tyrosine, with preservation of most of the ABA-Tyr moiety (ABA plus hydroxyphenyl portion of tyrosine). These derivatives were tested for the ability to stimulate ABA-L-Tyr specific T cell lines derived from B10.BR and B10.S mice. ABA-acetyltyramine, ABA-hydroxyphenylpropionic acid (ABA-PPr), and ABA-propylphenol, which lack either the carboxyl or amino group or both, could not induce T cell proliferation. The lack of stimulation by these derivatives was not due to their cytotoxic effects. A similar pattern of proliferation was obtained on stimulating lymph node T cells from B10.BR and B10.S mice primed with ABA-L-Tyr. Some differences were observed, however, between B10.BR and B10.S mice. ABA-L-Tyr-specific T cells from B10.BR mice could not respond well to ABA-D-Tyr in contrast to B10.S T cells. Furthermore, B10.BR mice primed with ABA-acetyltyramine or ABA-PPr in complete Freund's adjuvant could not induce ABA-L-Tyr-reactive T cells, whereas T cells from B10.S mice primed with these derivatives could proliferate in the presence of ABA-L-Tyr. The differences between B10.BR and B10.S mice were further investigated by using (B10.S X B10.BR)F1 mice. T cells from ABA-L-Tyr-immunized F1 mice responded poorly to ABA-D-Tyr when presented with B10.BR antigen-presenting cells (APC), but responded well when presented with B10.S APC. Similarly, T cells from ABA-PPr-primed F1 mice did not proliferate to ABA-L-Tyr in the presence of B10.BR APC, but could proliferate in the presence of B10.S APC. Our results clearly indicate that the presence of charged groups at the alpha-carbon of tyrosine plays a critical role in the triggering of ABA-L-Tyr-specific T cell proliferation. The significance of these results is discussed.     

Mdm20 Modulates Actin Remodeling through the mTORC2 Pathway via Its Effect on Rictor Expression

NatB is an N-terminal acetyltransferase consisting of a catalytic Nat5 subunit and an auxiliary Mdm20 subunit. In yeast, NatB acetylates N-terminal methionines of proteins during de novo protein synthesis and also regulates actin remodeling through N-terminal acetylation of tropomyosin (Trpm), which stabilizes the actin cytoskeleton by interacting with actin. However, in mammalian cells, the biological functions of the Mdm20 and Nat5 subunits are not well understood. In the present study, we show for the first time that Mdm20-knockdown (KD), but not Nat5-KD, in HEK293 and HeLa cells suppresses not only cell growth, but also cellular motility. Although stress fibers were formed in Mdm20-KD cells, and not in control or Nat5-KD cells, the localization of Trpm did not coincide with the formation of stress fibers in Mdm20-KD cells. Notably, knockdown of Mdm20 reduced the expression of Rictor, an mTORC2 complex component, through post-translational regulation. Additionally, PKCα^S657 phosphorylation, which regulates the organization of the actin cytoskeleton, was also reduced in Mdm20-KD cells. Our data also suggest that FoxO1 phosphorylation is regulated by the Mdm20-mTORC2-Akt pathway in response to serum starvation and insulin stimulation. Taken together, the present findings suggest that Mdm20 acts as a novel regulator of Rictor, thereby controlling mTORC2 activity, and leading to the activation of PKCα^S657 and FoxO1.     

Separation of Cl-Containing Chlorophylls by Column Chromatography

Using Toyopearl and cyclohexane: cyclohexanol solvent, fourCl-containing Chls were separated from ³⁶Cl-labeled cells ofthe blue-green, Plectonema boryanum. In normally grown cells,all four Cl-containing chlorophylls amounted to less than 1/2,000of the total Chi and about 1/50 of P700, values much lower thanpreviously reportedcontents of Chi RC I, and varied from algato alga. The level of Cl-containing Chi was markedly enhancedwhen the cells were poisoned with methyl viologen. These resultssuggests that these Cl-containing Chls are not related to thereaction center of PS I. (Received June 23, 1987; Accepted September 17, 1987)     

In vitro splicing of a chicken delta-crystallin pre-mRNA in a mammalian nuclear extract

An in vitro splicing system was constructed using portions of chicken delta-crystallin pre-mRNA synthesized in vitro and a HeLa nuclear extract. Analysis of the reaction products revealed that about 25% of the pre-mRNA was precisely spliced at 30 degrees C in 2 h under the standard conditions. The other major products of the reaction detected were a 5'-exon fragment and three RNA species showing unusual electrophoretic mobilities on polyacrylamide gels. Structural analyses showed that these three RNAs contain a branch (lariat) structure as seen in the in vitro splicing reactions of human beta-globin, adenovirus, and yeast pre-mRNAs. In addition, methylation at the N-7 position of the blocking guanosine of the 5'-terminal cap structure of pre-mRNA has been suggested to play an important role in the splicing reaction.     

Existence of endogenous inhibitors of platelet-activating factor (PAF) with PAF in rat uterus

Two kinds of phospholipids in normal rat uterus were found to inhibit the aggregation of washed rabbit platelets induced by 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (alkylacetyl-GPC) and were named Inhibitor I and Inhibitor II and identified by mass spectrometry. Inhibitor I was a mixture of 1-acyl (16:0, 18:0, 18:1, 18:2, and 20:4)-2-lyso-sn-glycero-3-phosphocholine (acyllyso-GPC) and 1-alkyl (16:0, 18:0, and 18:1)-2-lyso-sn-glycero-3-phosphocholine (alkyllyso-GPC). 16:0 acyllyso-GPC was the most inhibitory, followed by 18:1, 18:2, 20:4, and 18:0 acyllyso-GPCs and 16:0 alkyllyso-GPC. Their IC50 values were in the range of 1-4 X 10(-5) M against the platelet aggregation induced by 1 X 10(-10) M 16:0 alkylacetyl-GPC, indicating that they were about 100 times weaker inhibitors than CV-3988. Inhibitor II was a mixture of N-acyl sphing-4-enyl phosphocholine (18:1/18:0, 18:1/20:0, 18:1/24:0, and 18:1/24:2). The most inhibitory of these components were 18:1/20:0 and 18:1/24:0, followed by 18:1/24:2 and 18:1/18:0, and their IC50 values were in the range of 4-5 X 10(-5) M against platelet aggregation induced by the alkylacetyl-GPC. Quantitatively, about 10(5) times higher concentrations of these inhibitors should be necessary to inhibit platelet aggregation induced by 1 X 10(-10) M 16:0 alkylacetyl-GPC. In fact, the contents of Inhibitors I and II, respectively, were approximately 10(5) times (4.7 X 10(-2) and 7.1 X 10(-2) mol/mol lipid-phosphorus of the original uterine phospholipids) than that of 16:0 alkylacetyl-GPC (1.4 X 10(-6) mol/mol lipid-phosphorus). The role of alkylacetyl-GPC in normal rat uterus is uncertain, but it coexists in situ with two kinds of endogenous inhibitors, choline containing lysoglycerophospholipids and sphingophospholipids.     

Modulation of thrombin-stimulated lipid responses in cultured fibroblasts. Evidence for two coupling mechanisms

Treatment of cultured fibroblasts with thrombin results in the stimulation of cell division and lipid metabolism. Proteolytically active alpha-thrombin rapidly stimulates (a) release of arachidonic acid, (b) generation of inositol phosphates, and (c) increase in cellular diacylglycerol levels. Pretreatment of the fibroblasts with chymotrypsin before alpha-thrombin prevented the first two responses, (a) and (b), and reduced response c. Treatment of fibroblasts with gamma-thrombin, a proteolytic derivative of alpha-thrombin, produced a response indistinguishable from the alpha-thrombin treatment when preceded by chymotrypsin. These data support a model, similar to one for platelets [McGowan, E. B., & Detwiler, T. C. (1986) J. Biol. Chem. 261, 739-746], that fibroblasts possess two coupling mechanisms for the stimulation of lipid metabolism by thrombin. Similar to platelets, one mechanism, R1, mediates the stimulated release of arachidonic acid and is capable of activating Ni, a GTP-binding protein. R1 is inactivated by chymotrypsin and does not respond to gamma-thrombin. The other mechanism, R2, responds to gamma-thrombin and is not activated by chymotrypsin. In contrast to the mechanisms proposed for platelets, we demonstrate that the phospholipase C responsible for the hydrolysis of phosphoinositides is not activated by R2 but is activated via R1. Importantly, stimulation of either mechanism results in the elevation of cellular diacylglycerol. This indicates that the stimulated elevation of diacylglycerol, or those events dependent upon the elevation of diacylglycerol, is not a reliable indicator for establishing the hydrolysis of phosphoinositides.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in membrane constituents and chemiluminescence in vitamin E-deficient red blood cells induced by the xanthine oxidase reaction

The oxidation of vitamin E-deficient rat red blood cells (RBCs) induced by the hypoxanthine-xanthine oxidase (HX-XOD) system has been performed in an aqueous suspension. The generation of chemiluminescence and the accumulation of thiobarbituric acid-reactive substances (TBARS) were observed initially and were followed by hemolysis. Interestingly, the total counts of chemiluminescence were closely related to the amount of TBARS. The predominant change of membrane proteins induced by the reaction was the depletion of spectrin bands in gel electrophoresis. When RBC ghosts were oxidized with HX-XOD, the sulfhydryl (SH) groups of membrane proteins decreased at an early stage of the incubation, which was coincident with the above protein alteration. Membrane alpha-tocopherol suppressed not only the formation of TBARS but also chemiluminescence and hemolysis; nevertheless, it did not inhibit the protein damage and the loss of SH groups. Moreover, it was concluded that the chemiluminescence observed during the oxidation of RBC membranes was associated mainly with the peroxidation of lipids and only to a minor extent with the oxidation of proteins.