Histidine uptake and exchange in S 37 ascites tumor cells

The biological activity of hydrogen peroxide. VI. Mechanism of the enhancing effects of L-histidine: the role of the formation of a histidine-peroxide adduct and membrane transport

Further details of the mechanism of the enhancing effects of L-histidine (L-His) on the clastogenic activities of hydrogen peroxide (H2O2) were investigated. The L-His-H2O2 adduct was prepared and its physicochemical properties and biological activities were compared with those of a mixture of L-His plus H2O2 and of H2O2 alone. When the stabilities of the three test samples against glucose were determined in terms of residual H2O2 content in solutions of various pH values over the course of 11 days, the adduct was found to be more stable than H2O2 alone and very similar in terms of stability to the mixture. The almost equivalent stability of the adduct and the mixture suggested formation of the adduct in the mixture even though the interaction between L-His and H2O2 in solution seems, from 13C-NMR analysis, to be rather weak. In cell-free DNA after lysis of cell membranes, the induction of single-strand breaks (SSB) by the adduct and by the mixture was less effective than by H2O2 alone. These results contrast with previous results obtained in intact cells (Oya et al., 1992) and demonstrate the indispensability of the cell membrane for the enhancing effects of L-His. In the presence of inhibitors of the active transport of L-His, namely, 10 different neutral amino acids, effective suppression of the clastogenic activity of the adduct and of the mixture was observed, whereas four acidic and basic amino acids had no effect. Thus, the participation of active transport in the enhancing effects of L-His was apparent. The formation of the adduct of L-His with H2O2 brings about the stabilization or reduces the reactivity of H2O2 and, as a result, the induction of SSB is prevented to some extent in cell-free DNA systems. By contrast, in a cellular system, the accumulation of the adduct in cells by active transport is potentiated by the enhancing effect of L-His, although the mediation of some factors that can generate hydroxyl radicals (*OH) from the adduct in cells must be postulated.

Transport of L-histidine by human diploid fibroblasts in culture

The transport of L-histidine has been characterized in skin derived diploid human fibroblasts, cultured under strictly controlled conditions. The transport measurements were made on cells grown to subconfluency after 60 to 90 min timed preincubation. The data, at substrate concentrations ranging from 0.050 to 10 mmol/l, were analyzed by a computer program. A saturable transport system (Km = 0.25 mmol/l, Vmax = 17 nmol/mg protein per min) and a nonsaturable component of influx (Kd = 1.6 +/- 0.4 nmol/mg protein/min per mmol) were found. L-Histidine displayed no Na+ requirement at either low or high concentrations. Inhibition analysis demonstrated that L-histidine uptake at low concentration was poorly inhibited by amino acids known to be effective inhibitors of system A. The largest fraction of L-histidine uptake was inhibited by 2-amino-bicyclo (2,2,1)-heptane-2-carboxylic acid (BCH), leucine, and tryptophan. These results indicated that L-histidine is transported in human fibroblasts mainly by the Na+ independent system L. The differences between this cell type and others studied previously are discussed.

Inhibition of S37 ascites cell amino acid transport systems by alpha-chloromethylketone analogs

Alanine chloromethylketone and leucine chloromethylketone were synthesized and their effects on amino acid transport in sarcoma 37 mirone ascites tumor (S37) cells were studied. Alanine chloromethylketone preincubation weakly inhibited system A. Leucine chloromethylketone preincubation strongly inhibited both amino acid transport systems L and A. Leucine chloromethylketone was also a competitive inhibitor of leucine transport. Labeled leucine chloromethylketone was concentrated by S37 cells. Leucine chloromethylketone preincubation inhibition was concentration dependent and partial protection of transport was afforded by leucine. Steady-state retention of amino acids was decreased more than the initial velocity of transport by leucine chloromethylketone preincubation. Glutathione was also depleted. Labeled leucine chloromethylketone was incorporated in a plasma membrane protein fraction comigrating on a DEAE-cellulose column (DE52) with gamma-glutamyltranspeptidase activity. There was a modest increase in vital staining after treatment of S37 cells with leucine chloromethylketone, and glucose uptake was also inhibited. Whilst several effects occur during treatment of S37 cells with leucine chloromethylketone, it is suggested than one prominent effect is alkylation of amino acid transport system components.

The complete rate equation, including the explicit dependence on Na+ ions, for the influx of alpha-aminoisobutyric acid into mouse brain slices

The rate equation, including dependence on Na+-ion concentration for the influx of alpha-aminoisobutyric acid into mouse brain slices incubated in isotonic glucose medium at 37 degrees C, is v = 0.402 S/(1.02(1 + 788/[Na+]2)+S)+0.0477S, where v = influx in mu mol/min, g final wet wt of slices; [Na+] = concentbutyric acid in medium, in mM. This equation shows two kinetically independent, parallel pathways of concentrative uptake: one, saturable and dependent on Na+; the other, unsaturable and independent of Na+. Influx is independent of ionic strength, Cl- ion per se, and a moderate increase in tonicity. The binding of substrate to the saturable carrier depends on the Na+ concentration; the maximum capacity of this carrier does not. For transport, 2 Na+ ions must interact with each saturable transport site. This does not imply coupling between the flux of Na+ and the flux of alpha-aminoisobutyric acid.

Methionine transport in S37 cells. Substrate-dependent function of amino acid transport system A in exchange processes

Methionine had been observed to interact with two principal transport systems for amino acids in mammalian cells, the A and L systems. The present study of methionine transport and of exchange processes through system A arose in the course of a study to define the specificity of a transinhibition effect caused by cysteine. Methionine uptake through two transport systems in the S37 cell was confirmed by the occurrence of a biphasic double-reciprocal plot for labeled methionine uptake. Preloading cells with methionine stimulated labeled histidine uptake through systems A and L. Efflux of labeled methionine from cells was stimulated by histidine in a biphasic manner, so that bothe systems A and L can be used for exchange when methionine is the intracellular amino acid. Aminocycloheptanecarboxylic acid elicited exchange efflux of labeled methionine only through system L. ALPHA-Aminoisobutyric acid and N-methyl-alpha-aminoisobutyric acid both stimulated efflux of labeled N-methyl-alpha-aminoisobutyric acid from S37 cells. These findings are interpreted a showing that transport system A is capable of functioning as an exchange system depending upon the identity of intracellular and extracellular substrates available.

Heterogeneity of histidine transport in the Ehrlich cell

We have reexamined the heterogeneity shown by histidine in its uptake by the Ehrlich ascites tumor cell, in the face of a contradiction of our earlier interpretation. We again find the fraction of histidine uptake at neutral pH inhibitable by the model substrate for System A, 2-(methylamino)-isobutyric acid, to be fully dependent on the presence of Na+ or Li+. The small Na+ -independent component not attributable to System L can be identified with System Ly+ through its inhibitability by homoarginine. This component increases as the pH is lowered with an apparent pK' a of 6.1. The simultaneous decrease in the uptake by the neutral systems could be identified, for System L, with the same titration of histidine to its cationic form, but for System A the sharp decrease is identified with the protonation of a structure on the membrane rather than one on the substrate. The action of H+ in the latter case proved approximately non-competitive with Na+ when tested with ordinary substrates.

Biphasic kinetic plots and specific analogs distinguishing and describing amino acid transport sites in S37 ascites tumor cells

Curve-fitting procedures indicated that exo-2-amino-bicyclo-(2,2,1)-heptane-2-carboxylic acid (BCH) modified V and Km for one of two systems serving for histidine transport into the S37 ascites tumor cells. When this system was obliterated by leucine in the medium, BCH had no effect on histidine transport. Curve-fitting procedures similarly suggest N-methyl-alpha-aminoisobutyric acid affected the Km and V values for the other histidine-transporting system and that carboxymethylhistidine (His(Cm)) inhibited both transport systems. His(Cm) further inhibited histidine uptake into leucine-inhibited cells. Km and V values were altered simultaneously in the presence of several inhibitory analogs. Alanine methyl ester markedly inhibited high-concentration histidine uptake, whereas leucine methyl ester markedly inhibited low-concentration histidine uptake. The present results confirm earlier suggestions that our high c system is Christensen's A system and our low c system his L system. We also confirm a very high degree of specificity of N-methyl-alpha-aminoisobutyric acid for the A or high c system, and of BCH for the L or low c system. We suggest the utility of combining two approaches to the study of transport system properties; use of specific analogs and modification of biphasic plots. We demonstrate that the carboxyl group is not a prerequisite molecular feature for inhibitory interaction with the A or L system.

Transport of dibasic amino acids, cystine, and tryptophan by cultured human fibroblasts: absence of a defect in cystinuria and Hartnup disease

Transport of lysine, arginine, cystine, and tryptophan was studied in cultured skin fibroblasts from normal controls and from patients with cystinuria and Hartnup disease. Each of these amino acids was accumulated against concentration gradients by energy-dependent, saturable mechanisms. Lysine and arginine were each transported by two distinct processes which they shared with each other and with ornithine. In contrast, cystine was taken up by a different transport system with no demonstrable affinity for the dibasic amino acids. The time course and Michaelis-Menten kinetics of lysine and cystine uptake by cells from three cystinuric patients differed in no way from those found in control cells. Similarly, the characteristics of tryptophan uptake by cells from a child with Hartnup disease were identical to those noted in control cells. These findings indicate that the specific transport defects observed in gut and kidney in cystinuria and Hartnup disease are not expressed in cultured human fibroblasts, thus providing additional evidence of the important role that cellular differentiation plays in the regulation of expression of the human genome.