My thought would be that its another case of cost vs benefits.
Maintaining the metabolic pathways for 'unusual' amino acids has a cost
in protein synthesis, and turnover etc. These aa are only requried in
small quantities that can easily be obtained from dietry sources.
Theregular amino acids are needed in much larger quantities, possibly
more than can be easily provided from dietry sources, and are in general
simpler (therefore less energetically expensive) to sysnthesize.
BTW This suggets the possibility of 'dormant pathways' We may have all
the genes nec for synthesizing essential aa but they may be turned off
(semi-) permanently. Anyone have any thoughts on that one?
Actually in soem ways I prefer the original explanation for some aa, esp
ones like Glutamine, glutamate etc. that are central in energy
metabolism.
____
Cameron Neylon, Honours, Dept of Biochemistry,
University of Western Australia
(09) 368-2717 or more regularly camn at uniwa.uwa.edu.au
Biochemistry: noun, The art of sitting, late at night, transferring
ridiculously small volumes of liquid with one hand and
attempting to hold onto one's sanity with the other.
