Sytkowski A J, Vallee B L
Biochemistry. 1979 Sep 18;18(19):4095-9. doi: 10.1021/bi00586a006.
The noncatalytic and catalytic zinc atoms of horse liver alcohol dehydrogenase, [(LADH)Zn2Zn2] or LADH, have been replaced differentially with 109Cd by equilibrium dialysis, resulting in two new enzymatically active species, [(LADH)109Cd2Zn2] and [(LADH)109Cd2109Cd2]. The UV difference spectra of the cadmium enzymes vs. native [(LADH)Zn2Zn2] reveal maxima at 240 nm with molar absorptivities, delta epsilon 240, of 1.6 X 10(4) M-1 cm-1 per noncatalytic 109Cd atom and 0.9 X 10(4) M-1 cm-1 per catalytic 109Cd atom, consistent with coordination of the metals by four and two thiolate ligands, respectively, strikingly similar to the 250-nm charge-transfer absorbance in metallothionein. Carboxymethylation of the Cys-46 ligand to the catalytic metal in LADH presumably lowers the overall stability constant of the coordination complex and results in loss of catalytic 109Cd or catalytic cobalt but not catalytic zinc from the enzyme.
马肝醇脱氢酶[（LADH）Zn₂Zn₂]或LADH的非催化性和催化性锌原子已通过平衡透析被¹⁰⁹Cd分别不同程度地取代，产生了两种新的具有酶活性的物种，即[（LADH）¹⁰⁹Cd₂Zn₂]和[（LADH）¹⁰⁹Cd₂¹⁰⁹Cd₂]。镉酶与天然[（LADH）Zn₂Zn₂]的紫外差光谱显示，在240 nm处有最大值，每个非催化性¹⁰⁹Cd原子的摩尔吸光系数Δε₂₄₀为1.6×10⁴ M⁻¹ cm⁻¹，每个催化性¹⁰⁹Cd原子的摩尔吸光系数为0.9×10⁴ M⁻¹ cm⁻¹，这分别与金属由四个和两个硫醇盐配体配位一致，与金属硫蛋白中250 nm处的电荷转移吸光度极为相似。LADH中与催化性金属结合的半胱氨酸-46配体的羧甲基化可能会降低配位复合物的整体稳定常数，并导致酶中催化性¹⁰⁹Cd或催化性钴而非催化性锌的丢失。
