TABLE 1.

Comparison of parameters obtained from pre-steady-state analyses of yeast and human CBS

Parameter	Human CBS	yCBSa
Kd(app) for Serb	2.04 ± 0.72 mm	14.4 ± 1.7 mm
kobs (AA from Ser)	0.96 ± 0.02 mm−1 s−1	38.0 ± 3.0 mm−1 s−1
Kd(app) for Cysb	7.4 ± 1.5 mm	ND
kobs (AA from Cys)	0.38 ± 0.01 mm−1 s−1	1.61 ± 0.3 mm−1 s−1,c 4.1. ± 0.2 mm−1 s−1d
Kd(app) for cystathionineb	2.5 ± 0.7 mm	1.6 ± 0.3 mm
kobs (AA from cystathionine)	0.38 ± 0.01 mm−1 s−1	4.1 ± 0.2 mm−1 s−1
Km(app) for Hcy,e Kd(app) for Hcy,f	2.1 ± 0.5 mm	0.37 ± 0.02 mm
kobs (aldimine from AA)g	ND	183 ± 4 mm−1 s−1
kmax (aldimine from AA)	40.6 ± 3.8 s−1	ND

^a The values for yCBS are taken from Ref. 23.

^b The K_d(app) values listed for human CBS were derived from the dependence of k_obs on the respective substrate concentrations as discussed under “Results.”

^c The values represent the rates for Reaction 3 in Fig. 1.

^d The values represent the rates for Reaction 4 in Fig. 1.

^e This parameter was determined for human CBS. Hyc, homocysteine.

^f This parameter was determined for yCBS.

^g AA, aminoacrylate; ND, determined.