The current count of human P450s stands at 53 genes plus one candidate 2A gene
that is partial. There are 22 pseudogenes. I have
dropped some of the 2D pseudogenes from this count since there appears to be
only 1 2D6 gene and 2 pseudogenes. The others are various alleles of these
three formed by deletion and rearrangements. The 2C9, 3A4, 11B1, 11B2 and 26A1
genes are not present in the genomic sequence from the human genome project.
The estimates of completion are now around 85%, so this leads to a back of the
envelope calculation of 54 genes – 5 not in genomic DNA = 49 genes/0.85 = 58
genes predicted. There might be four more unknown P450 genes left to find in
the last 15% of the human genome. I would be surprised if the final count
exceeded 60 functional P450 genes.
The human chromosome 21 sequence was announced this week. I examined it for
P450 genes and found the author’s have annotated one pseudogene of the 4F family
on chromosome 21. It has been named CYP4F28P and I have posted it to my human
P450 sequence file. It is 81% identical to CYP4F25P and 80% identical to
CYP4F26P. The 4F family seems to generate a lot of pseudogenes, more so than
other families.
I am trying to keep up with the new human sequences, but revisions of old
sequences are rapidly replacing the ones I have already posted on my PDF files
of human P450 genes. This means the nucleotide numbering of the exon locations
will be changing.
The sequence previously named CYP4AH1 has been renamed to CYP4V2 since it
matches to a rainbow trout P450 fragment sent to me long ago and named CYP4V1.
The two are 69% identical.
Be aware that there is one P450 in the database that is labeled incorrectly as
human (AC021892). This is a rice CYP75 sequence from rice chromosome 10. It
was accidentally labeled as being from human chromosome 10 in the definition
line. The authors are trying to get this corrected since it affects many
entries.