Rat liver 4S-benzo[a]pyrene-binding protein is distinct from glycine N-methyltransferase.
Rat liver 4S-benzo[a]pyrene-binding protein (BAP) was reported to be identical to the subunit (Mr 32,500) of the tetrameric glycine N-methyltransferase (GNMT). We have reevaluated this study. When a liver cytosol was subjected to Sephacryl S-200 gel permeation chromatography, enzyme activity as well as cross-reactivity with anti-GNMT antibody were found only at the elution position of the purified GNMT. Chromatograph of the cytosol pretreated with [3H]benzo[a]pyrene showed two peaks in the void volume and at the position of an approximate Mr of 40,000. The latter, corresponding to the 4 S BAP, did not cross-react with the anti-GNMT antibody. An extract of nuclei in which GNMT was proposed to act as a mediator of cytochrome P4501A1 gene expression contained the tetrameric GNMT but no binding activity. The lung, in which no GNMT mRNA occurred, had the 4 S BAP. Extracts of Escherichia coli and COS-7 cells expressing large amounts of GNMT showed no 4 S BAP. These findings suggest that the 4 S BAP is distinct from the subunit of GNMT.
Ogawa
H
H
Department of Biochemistry, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan. hogawa@ms.toyama-mpu.ac.jp
Gomi
T
T
Imamura
T
T
Kobayashi
M
M
Huh
N
N
D000444:Aldehyde Dehydrogenase; D000818:Animals; D000906:Antibodies / Q000276:immunology; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000276:immunology; D002850:Chromatography, Gel; D003429:Cross Reactions; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D050938:Glycine N-Methyltransferase; D008099:Liver / Q000737:chemistry* / Q000201:enzymology; D008780:Methyltransferases / Q000737:chemistry* / Q000276:immunology; D008970:Molecular Weight; D051381:Rats
C488945:4S benzo(a)pyrene-binding protein, mouse; D000906:Antibodies; D002352:Carrier Proteins; C032445:benzopyrene carrier protein, mouse; D019363:Cytochrome P-450 CYP1A1; C488942:4S benzo(a)pyrene-binding protein, rat; D000444:Aldehyde Dehydrogenase; D008780:Methyltransferases; D050938:Glycine N-Methyltransferase; C494512:Gnmt protein, rat