Structural and biochemical work on the enzymes taurine a-ketoglutarate dependent dioxygenase TauD (Esherichia coli), cysteine dioxygenase CDO (Homo sapiens) and cysteine sulfinic acid decarboxylase CSAD (Homo sapiens) have provided the necessary groundwork from which biomedical studies can now proceed in studying disease states associated with the taurine metabolic pathway and the respective enzymatic family members. TauD is the enzyme responsible for the conversion of taurine (2-aminoethanesulfonate) to sulfite and aminoacetaldehyde while concurrently decomposing a.-ketoglutarate to succinate and carbon dioxide. Expressed during conditions of sulfur starvation, TauD enables the cell to utilize taurine, and other similar sulfonates as an alternative sulfur source. The crystal structure of TauD solved in the apo (1.9 resolution, Rcryst=21.2%, Rfree=24.9%) and holo (2.5 resolution, Rcryst=22.5%, Rfree=24.9%) forms revealed two possible dimeric arrangements; the one supported in this work has a significant amount of evidence to suggest the functional importance of dimerization. The 2-his 1-carboxylate facial triad was identified in this structure as well as the residues involved in substrate binding for both taurine and a.-ketoglutarate. From this structure a feasible reaction mechanism is proposed and is currently being tested through mutagenic and crystallographic studies. A significant area of interest is the method of oxygen activation, which remains unclear. Studies with another dioxygenase, CDO, hope to provide insight into the method of oxygen activation. CDO and CSAD are the two enzymes involved in the taurine biosynthetic pathway primarily located in the human brain, heart, liver, and central nervous system. Since taurine is a known osmoregulator, neurotransmitter, radical scavenger, and is central to the cholesterol excretion pathway, any information gathered on these enzymes provides the base for future disease research. The recombinant expression of human CDO and CSAD is new research. Two forms of CDO were observed, a 23 kDa form and a 25 kDa form. Here we report the expression, purification, and kinetic information for CDO.