Antioxidants in neoplastic cells: IV. Evidence that the phenolic antioxidant A274 is 9-(4-hydroxyphenyl)xanthene, an artifact in tissue culture media.

An extensively conjugated phenol (A274), recently shown to be present as a common trace constituent in randomly selected batches of commercial tissue culture media, was diazomethylated; the monomethyl derivative so prepared was shown to exhibit gas chromatographic and mass spectrometric properties identical to those observed for synthetically prepared 9-(4-methoxyphenyl)xanthene, but different from those of several isomeric compounds. The structure 9-(4-hydroxyphenyl)xanthene is thus proposed for A274.

Binding of adenosine 5'-monophosphate to bovine liver fructose 1,6-bisphosphatase.

Bovine liver fructose 1,6-bisphosphatase bound 4 mol of its allosteric inhibitor AMP per mole of enzyme with half-saturation at 17 mumol/l AMP. The presence of a mixture of positive and negative cooperativity in the binding of AMP to the enzyme was suggested by several procedures for analyzing binding data. In particular, calculation of the intrinsic binding constants for AMP yielded the relationships: K1' less than K2' greater than K3' less than K4', indicating mixed cooperativity.

Effects of metal ions and selenoamino acids on induction of glutathione peroxidase in mouse neuroblastoma.

The induction of glutathione peroxidase in mouse neuroblastoma cells by selenite is enhanced by equimolar amounts of arsenate, arsenite, molybdate, chromic or dichromate ions. At equimolar selenium concentration, selenite, selenocystine and selenomethionine induced glutathione peroxidase activities having the ratios 4:4:1. Protein synthesis inhibitors prevented the induction of glutathione peroxidase by selenite indicating that de novo protein synthesis is required.

Antioxidants in neoplastic cells: II. Isolation and partial characterization of a phenolic antioxidant from differentiated mouse neuroblastoma cells.

The generation of an antioxidant has been shown to be associated with the dramatic increase in resistance to lipid peroxidation which occurs during the differentiation of mouse neuroblastoma cells in culture. The antioxidant has been isolated from the neuroblastoma neutral lipid fraction and partially characterized by means of low-resolution and high-resolution mass spectrometry and other lines of evidence. All presently available information suggests that this antioxidant is a highly aromatic, monosubstituted phenol having the molecular formula C19H14O2.

Antioxidants in neoplastic cells: I. Changes in the antioxidative capacity of mouse neuroblastoma cells measured by a single-phase assay.

Cultured mouse neuroblastoma cells exhibit a striking increase in antioxidative capacity during the transition from logarithmically dividing cells to nondividing, neurite-bearing cells. Two physically separable phenomena are involved: (a) the membrane pellet of neurite-bearing cells is highly resistant to lipid peroxidation, and (b) the postmicrosomal supernatant of these cells inhibits peroxidation in rat liver mitochondria and other biological membranes. A precise, single-phase assay has been developed for assessing antioxidant levels in lipid extracts. By means of this assay, the increase in membrane resistance to lipid peroxidation has been correlated with a threefold increase in the antioxidant activity of the neuroblastoma neutral lipid fraction. This finding implies that generations of a neutral lipid antioxidant (or antioxidants) is involved in the profound increase in antioxidative capacity which occurs in differentiating neuroblastoma cells.