Triosephosphate isomerase (TIM) is one of the enzymes involved in glycolysis. It is found in a wide variety of organisms, since most organisms perform glycolysis. It catalyses the interconversion of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (see Fig. 1). This effectively enables a doubling of the yield from the glycolysis of a single glucose molecule.
TIM occurs as a dimer, with two identical barrel shaped chains. This can be seen in the Rasmol image of yeast TIM (MMDB Id: 2490, PDB Id: 1YPI).
Biologists use the way in which sequence similarity of a certain protein
among different organisms to hypothesize evolutionary branching. The proetin
is thus used as a "molecular clock". TIM is a good choice for such an analysis
since it is found in organisms of all varieties. We shall now attempt to
do such an analysis for the five genome organisms, TIM as our "molecular
clock". The appropriate GenBank entries are as follows:
|Organism||Amino acid sequence?||Nucleotide sequence?|
|Homo sapiens||Yes||Yes, cDNA|
|Saccharomyces cerevisiae||Yes||Yes, whole gene|
|Mus musculus||Yes||Yes, mRNA|
|Drosophila melanogaster||Yes||Yes, whole gene|
|Caenorhabditis elegans||Yes||Yes, whole gene|
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