Subject: Why are GTP used instead of ATP?

I dont understand why is GTP used in some reaction in place of ATP eg. in
gluconeogenesis.
    While ATP and GTP are energetically equivalent (i.e., the same amount of
energy can be harnessed from ATP as from GTP), their use in biochemical
reactions is enzyme-dependent. Some enzymes, such as succinyl-CoA synthetase,
use GTP to drive catalysis. Others, like hexokinase, require ATP instead. Which
nucleotide gets used depends heavily on the specificity of the enzyme in
question, which in turn depends on the enzyme's amino acid composition and
secondary/tertiary structures.
    Also, for what it's worth, the production of GTP instead of ATP by certain
enzymes is inconsequential since GTP can be converted to ATP via substrate-level
phosphorylation.
    I believe there is also an anabolic/catabolic and
protein/fat/carbohydrate/nucleic acid distinction at work in there as well. My
guess is there is separation to allow the cell to target energy resourses to
specific pathways. Why GTP?????

Re: Why are GTP used instead of ATP?