numeral denoting subfamily (1, 2, 3 . . .), and in a few instances,
a lower case letter denoting allelic variants of the same
gene (a, b, c . . .). As with the cytochrome P450 enzymes,
genes are usually denoted in italics, whereas the subunit protein
is shown in standard font. The functional GST enzymes
exist as dimeric proteins, and only subunits within the same
class can form heterodimers (e.g., alpha subunits can dimerize
with other alpha subunit types, but not with mu or pi subunits).