Direct interaction between a quinoline derivative, MS-209, and multidrug resistance protein (MRP) in human gastric cancer cells

MS-209 is a novel quinoline derivative reversing P-glycoprotein-mediated multidrug resistance (MDR). We investigated the interaction between MS-209 and multidrug resistance protein (MRP) in MRP-overexpressing human gastric cancer cells. We measured [3H]leukotriene C4 uptake into the membrane vesicles of the cells and intracellular calcein and [3H]vincristine accumulation with or without MS-209. In multi-drug-resistant MKN45R0.8 cells selected by doxorubicin, MS-209 dose dependently reduced MRP-mediated [3H]leukotriene C4 uptake and increased calcein accumulation. In both resistant and unselected cell lines expressing the MRP gene, MS-209 increased [3H]vincristine accumulation in proportion with the level of MRP mRNA expression and enhanced the cytotoxicity of etoposide, doxorubicin, and vincristine. The reversal effects correlated with the level of MRP mRNA expression in these cells. Our results indicate that MS-209 effectively reverses intrinsic and acquired MRP-mediated MDR of gastric cancer cells by interacting directly with MRP.     

Microbial distribution of selenocysteine lyase.

We studied the distribution of selenocysteine lyase, a novel enzyme catalyzing the conversion of selenocysteine into alanine and H2Se, which we first demonstrated in various mammalian tissues (Esaki et al., J. Biol. Chem. 257:4386-4391, 1982). Enzyme activity was found in various bacteria such as Alcaligenes viscolactis and Pseudomonas alkanolytica. No significant activity was found in yeasts and fungi. Selenocysteine lyases from A. viscolactis and P. alkanolytica acted specifically on L-selenocysteine and required pyridoxal 5'-phosphate as a cofactor.     

The effect of carboxylates and halides on L-lysine 6-aminotransferase-catalyzed reactions

L-Lysine:2-oxoglutarate 6-aminotransferase catalyzes very slow transamination between L-alanine and 2-oxoglutarate. A high concentration of anions such as formate, acetate and halides greatly accelerated this transamination without affecting the affinity of the enzyme for L-alanine. In contrast, the anions strongly inhibited the normal L-lysine 6-transamination in a competitive manner with L-lysine and in a non-competitive manner with 2-oxoglutarate. This result suggests that the enzyme has an anion binding site which normally binds the carboxyl group of L-lysine. The binding of halides or carboxylates to this site probably induces a conformational change of the enzyme, and results in the inhibition of L-lysine 6-transamination, and in the stimulation of L-alanine transamination. Treatment of the enzyme with an arginine-specific dicarbonyl reagent, phenylglyoxal, led to a loss of the enzyme activity for L-lysine. The activity for L-alanine was not affected, but the stimulating effect of anions on L-alanine transamination was impaired. Thus, it is suggested that an arginine residue(s) plays an important role in the anion binding site.     

Transendothelial transport (transcytosis) of iron-transferrin complex in the bone marrow

To determine the transport pathway of iron-transferrin complex (Fe-TF) across the marrow-blood barrier, we labeled Fe-TF with colloidal gold and perfused rat femoral marrow with this probe. At 4 degrees C, the probe bound to the luminal surface of marrow sinus endothelium. The binding was inhibitable in the presence of excess native Fe-TF indicating the specificity of the binding. At 37 degrees C, the probe was internalized largely via a system of coated pits and vesicles and transported across the endothelium via a system of tubules and endosomal vesicles. It could not be ascertained if all Fe-TF was still associated with the colloidal gold probe within the endothelium, but the probe appeared to be externalized on the abluminal side into the interstitium where it subsequently bound to the surface of marrow erythroblasts and was internalized. Endothelium appeared to store part of the probe within a large vesicular system. No transport of Fe-TF was noted through diaphragmed fenestrations, diaphragmed vesicles, or interendothelial junctions. No endothelial uptake of this magnitude was noted when native gold particles or gold-labeled bovine serum albumin was used. Our findings indicate that in the bone marrow, gold-labeled Fe-TF is first taken up by sinus endothelium through a receptor-mediated mechanism and is possibly transported transendothelially via a vesicular system (transcytosis).     

Thermostable alanine dehydrogenase of Bacillus sp. DSM730: gene cloning, purification, and characterization

We have cloned the thermostable alanine dehydrogenase (EC 1.4.1.1) gene from a thermophile, Bacillus sp. DSM730, into Escherichia coli C600 with a vector plasmid, pBR322. The enzyme was overproduced by the transformed cells, and purified to homogeneity with a yield of 69% by heat treatment and another step. The enzyme has a molecular weight of about 250,000 and consists of 6 subunits identical in molecular weight (43,000). It is not inactivated by heat treatment at 75 degrees C for 60 min, or incubation in the pH range of 5.5-10.5 at 55 degrees C for 10 min. The enzyme ctalyzes the oxidative deamination of L-serine in addition to L-alanine. The oxo analogue of serine is as reactive as pyruvate. Thus, the enzyme differs markedly from alanine dehydrogenases so far studied.     

Erythrocytes of Japanese Quail for Hemagglutination by Rubella Virus

Erythrocytes (RBC) of adult Japanese quail, Coturnix coturnix japonica, were found to be as sensitive as day-old chick RBC for rubella virus hemagglutination (HA). Various factors involved in the HA were studied with quail RBC as well as with adult pigeon and day-old chick RBC. Pigeon RBC, unlike chick and quail RBC, tended to show, without hemagglutinin, a pattern of sedimented RBC resembling the HA pattern by the virus at 4 C, to a lesser extent at room temperature, in 0.85% NaCl solution buffered with m/100 phosphate (PBS), and were prevented from doing so by addition of a small amount of bovine plasma albumin to the diluent. A small amount (about 10^?3 m ) of CaCL₂ in PBS gave higher HA titers. The HA titer was higher at 4 C than at room temperature and much reduced at 36 C with chick and quail RBC. With pigeon RBC, addition of bovine plasma albumin to the diluent tended to reduce HA titers. The HA titer was highest at pH 5.8 to 6.8, and was inversely proportional to the RBC concentration. Under the conditions established on the basis of these findings, chick and quail RBC gave similar HA titers, but pigeon RBC gave consistently higher titers. However, these types of RBC gave no significant difference in HA-inhibiting antibody titer when 4 units of hemagglutinin as determined with the homologous RBC was used.     

Preliminary crystallographic study of omega-amino acid: pyruvate aminotransferase from Pseudomonas sp. F-126.

Large single crystals of ω-amino acid: pyruvate aminotransferase, were prepared by dialysis of the enzyme solution against 2.2 m-ammonium sulphate solution at pH 7.8. X-ray diffraction patterns show that the crystals belong to the orthorhombic space group I222 or I2₁2₁2₁ with unit cell dimensions $\text{a = 124.1}\text{A}\text{?}\text{, b = 137.9}\text{A}\text{?}\text{, and}\text{c = 61.2}\text{A}\text{?}$. The asymmetric unit consists of one monomer of molecular weight 43,000.