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Biomedical subjects

N J Lewis

Publications and source records attributed to N J Lewis.

52 records · Page 3Linked to original sources
PubMed1978

Synthetic sulfur-containing amino acids. Inhibition of transport systems in S37 ascites tumor cells.

The preparation of a series of synthetic sulfur-containing amino acids is described. These compounds included heterocyclic analogues of L-cysteine, DL-norcysteine, and DL-homocysteine. The amino acids were assessed for their ability to inhibit the neutral amino acid transport systems of the Sarcoma 37 ascites tumor cell and their inhibitions were compared with those of L-methionine and L-ethionine. Transport studies indicated that the amino acids synthesized were capable of inhibiting the uptake of [3H]-L-histidine in the S37 cell.

Amino Acids↗
PubMed1978

The differentiation and calcification of chondrocytes in primary cell cultures.

The cartilage from a non-immobilized fracture undergoes a series of morphological and biochemical changes resembling the in vivo differentiation and calcification in the epiphyseal plate. The studies reported here demonstrate that a homogeneous population of chondrocytes isolated from fracture callus fibrocartilage undergoes the same changes in vitro. Chondrocyte primary cultures were grown for 28 days during which time the morphological, histological and histochemical properties of the cultures were studied. Demonstrated by various histological procedures, chondrocytes synthesized the characteristic cartilage matrix, and progressively calcified with increased culture age. This system can be used to elucidate the cellular and molecular mechanisms of calcification.

Animals↗
PubMed1977

The genetic control of molybdoflavoproteins in Aspergillus nidulans. A xanthine dehydrogenase I half-molecule in cnx- mutant strains of Aspergillus nidulans.

The cnx- group of mutants of Aspergillus nidulans lacks xanthine dehydrogenase (xanthine: NAD+ oxidoreductase, EC 1.2.1.37) and nitrate reductase (EC 1.6.6.3) activities and are thought to be defective in the synthesis of a molybdenum-containing cofactor, 'cnx', common to xanthine dehydrogenase and nitrate reductase [Pateman, J.A., Rever, B.M., Cove, D.J. and Roberts, D.B. (1964) Nature (Lond.) 201, 58-60]. The cnx cofactor has a role in maintaining the aggregated multimeric structure of nitrate reductase [MacDonald, D.W., Cove, D.J. and Coddington, A. (1974) Mol. Gen. Genet. 128, 187-199]. We report here that, in cnx- mutants grown under conditions inducing xanthine dehydrogenase I, a species cross-reacting with antisera to the native enzyme and of half its molecular weight is present, together with cross-reacting molecules of similar molecular weight to the native enzyme. This suggests that the cnx cofactor has a role in maintaining the aggregated structure of xanthine dehydrogenase I. Both cross-reacting species are capable of passing reducing equivalents from NADH to a tetrazolium salt, showing that the cnx cofactor is not necessary for enzymic activity towards NADH.

Aspergillus nidulans↗
PubMed1977

Pesticide induced ouabain resistant mutants in Chinese hamster V79 cells.

The effect of 3 insecticides (chlordane, dieldrin and carbaryl) and one herbicide (2,4-D-fluid) was studied on the induction of ouabain-resistant mutants in Chinese hamster V79 cells at concentrations approaching the Environmental Protection Agency (EPA) tolerance limits. The kinetics and dose range for cytotoxicity were determined by colony formation assay. Results showed that these compounds enhanced the number of ouabain-resistant mutants and acted as weak mutagens.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1977

Pesticide induced DNA damage and its repair in cultured human cells.

The effects of pesticides on the induction of unscheduled DNA synthesis in SV-40 transformed human cells (VA-4) in culture with and without metabolic activation by liver microsomes was studied. Results showed that ten of the thirteen compounds examined either directly or upon metabolic activation induced unscheduled DNA synthesis in the human cell system used. The DNA repair kinetics and size of the repaired regions resulting from treatment with four of the chemicals (Carbaryl, Chlordane, Dieldrin and 2.4-D Fluid) were studied by 313 nm photolysis of repaired regions containing bromodeoxyuridine (BUdR). The size of the repaired regions differed between compounds but could generally be classified as either of the X-ray (short) or UV-type (long).

Cell Line↗
PubMed1975

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.

Alanine↗
PubMedDate not supplied

[14C]leucine chloromethylketone interaction with sarcoma 37 cell plasma membrane components.

Leucine chloromethylketone labeling of viable S37 cells was preferential for the plasma membrane fraction. The pattern of radiolabeling of the plasma membrane proteins was time dependent. After 5 min the radiolabel was localized with glutamyl transpeptidase, and subsequently with other physiologically active proteins as a function of time after incubation. Labeling of proteins was temperature dependent and incubation of viable S37 cells with the radiolabeled substrate at 0 degrees C yielded little or no radioactivity localized in the plasma membrane. The molecular weight of one radiolabeled substrate--membrane protein complex was estimated on sodium dodecyl sulfate polyacrylamide gel electrophoresis to be between 100,000-200,000.

Amino Acid Chloromethyl Ketones↗