Molecular Cloning and Nucleotide Sequence of DNA of Mitochondrial Cytochrome P-450(11β) of Bovine Adrenal Cortex1

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Abstract
CDNA clones of the mRNA for bovine adrenal cytochrome P-450(11β) were isolated. Sequence analysis of a 4 kb long cDNA revealed the primary structure of P-450(11β), which consisted of 503 amino acids (Mr: 57, 924) and contained an extension peptide of 24 amino acids at the NH2-terminus of the mature P-450(11β) molecule. A bovine genomic DNA containing the 1st exon and its leader sequence of P-450(11β) gene was also isolated from a bovine gene library. Determination of the transcription initiation site by SI nuclease analysis using the cloned genomic DNA confirmed that the methionine codon near the 5' side of the 4 kb long cDNA was the initiation codon. Comparisons of the primary structures among P-45O(11β) and other forms of cytochrome P-450 including P-450(SCC) indicated that the two mitochondrial P-450s, P-450(11β) and P-450(SCC), were significantly different from microsomal forms of cytochrome P-450. The homology between P-45O(11β) and P-450(SCC), was 36%, which is higher than the values between P-450(11β) and various microsoraal P-450s. An alignment of P-45O(11β) and P-450(SCC) to give maximum matching showed four highly conserved regions (C-l, C-2, C-3, and C-4). The homology values of these regions were 58–70%, considerably higher than the overall homology between these two mitochondrial P-450s. A putative heme binding site and a steroid binding site were located in the conserved regions. Hydropathy profiles of P-45O(11β) and P-450(SCC) were very similar. A definite difference was noticed at the NH2terminal portion between mitochondrial and microsomal types of P-450. Microsomal type of cytochrome P-450 had a hydro-phobic sequence consisting of about 20 amino acids, whereas mitochondrial type had an extension peptide containing many positively changed amino acids.

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