The inhibition of glyceradehyde-3-phosphate dehydrogenase by benz(a)anthracene and its derivatives after exposure to laboratory lighting

Photooxidation products of 7,12-dimethylbenz[a]anthracene

The principal products of the photooxidation of 7,12-dimethylbenz[a]-anthracene (DMBA) in aqueous solutions by photooxidation induced by laboratory lighting have been characterized by high performance liquid chromatograms (HPLC), ultraviolet and mass spectrograms and by comparisons with authentic samples. The products identified were the 7,12-epidioxy-7,12-dihydro-7-12-dimethyl-, 7,12-dione, 7-hydroxymethyl-12-methyl-, 12-hydroxymethyl-7-methyl-, 7-formyl-12-methyl-, 12-formyl-7-methyl-, and 12-hydroxy-12-methyl-7-one derivatives of benz[a]-anthracene. The HPLC profile of products is similar to that obtained from oxidation of DMBA by 'one-electron' reagents, singlet oxygen, or liver microsomal metabolism. The first points of attack are the 7- and 12- positions. The mechanism of photooxidation appears to be generation of singlet oxygen by photodynamic effect of DMBA. None of the products is photosensitizing, however.

The binding of benz(a)anthracene derivatives to glyceraldehyde-3-phosphate dehydrogenase and mammary tissue following exposure to laboratory light

7,12-Dimethylbenz(a)anthracene (DMBA) and 7-methoxymethyl-12-methylbenz(a)anthracene (MeO-DMBA) are converted to a number of products during short exposures in aqueous suspension to laboratory illumination. The mixture of products binds to glyceraldehyde-3-phosphate dehydrogenase (GPDH) while inhibiting its activity but there is no apparent relationship between the binding and inhibition of enzyme activity. There is little, or no, binding or enzyme inhibition when the compounds are protected from light. 7-Bromomethyl-12-methylbenz(a)anthracene (Br-DMBA) binds to GPDH whether photoactivated or not but enzyme inhibition depends upon light exposure. The binding of light-exposed DMBA by surviving rat mammary tissue was five-times greater than with the unchanged hydrocarbon. Binding of MeO-DMBA products also occurred after light exposure but not in the dark.