US EPA

2212170 

Journal Article 

Mechanism for the differential induction of mutation by S9 activated benzo[a]pyrene employing either a glucose-6-phosphate-dependent NADPH-regenerating system or an isocitrate-dependent system 

Lindblad, WJ; Jackim, E 

1982 

1 

Mutation Research
ISSN: 0027-5107
EISSN: 1873-135X 

109 

1 

109-118 

English 

6289094 

10.1016/0027-5107(82)90021-5 

WOS:A1982PE58100010 

The biochemical parameters contributing to the disparity in mutation frequencies calculated for benzo(a)pyrene (50328) (BP) using the glucose-6-phosphate dependent (G6P) NADPH regenerating system and the isocitrate (IC) dependent system were assessed in CHO-K1 cells. Both systems used rat liver S9 homogenate as substrate but differed in the production of reduced NADP. Total aryl hydrocarbon hydroxylase (AHH) activity was greater for the isocitrate dependent system relative to the G6P dependent system although the isocitrate system yielded a lower number of HGPRT mutants. AHH activity was significantly affected by pH and NADP concentration, but these parameters did not account for the difference in activity between the G6P and IC dependent systems. Examination of tritiated BP distribution within cells after exposure to calcium-phosphate indicated that the precipitation of calcium-phosphate in the G6P system increased internalization of BP resulting in decreased AHH activity. The authors suggest that cofactors for the G6P regenerating system result in insoluble particulates which facilitate entry of BP and its metabolites into the cells. BP metabolites produced by the S9 preparation were analyzed by reverse phase high pressure liquid chromatography. The G6P system produced greater levels of mutation with lower levels of total metabolites and yielded a higher percent of the strongly mutagenic form, 7,8-dihydroxybenzo(a)pyrene, which, the authors conclude, may be a contributing mechanism for elevation of the mutation frequency with the procedure.