Structure of Dehydrogenase and Substrate Binding

The HLADH is a dimer of molecular weight of about are at least two distinctive types of subunits, E ( and S (steroid active). These two types differ in six amino acids, which seems to be the origin of the their catalytic properties (Jdrnvall 1970a,b). The only one of the six amino acids by another one appearance of steroid activity (Eklund et al. 1976). the steroid activity is an intrinsic property of the than the activity toward ethanol because the latter bodily constituent (Damgaard 1981). 

There ethanol active) the position of difference in replacement of results in the It seems that enzyme rather is not a normal 

HLADH contains two zinc ions per subunit. One of the zinc ions is called the catalytic zinc and is located in the active site of the enzyme (Sigman 1967). The catalytic zinc can be specifically depleted with concomitant loss of enzymatic activity or substituted by other metal ions with distinctly reconstituted activities. The enzyme is strongly inhibited by metal chelating agents such as pyrazole, which has been well exploited by studies of the reaction mechanism (McFarland and Bernhard 1972, Schmidt et al. 1979). The other zinc ion, the structural zinc , is used to maintain the three-dimensional structure of the enzyme. 

On the other hand, YADH is a tetramer of molecular weight of about 145000 and each subunit has only one zinc ion which is catalytic . In spite of these differences, the fundamental 

X-ray crystallographic studies have been made extensively on HLADH and it is known that each subunit is divided into two domains, that is, coenzyme-binding and catalytic domains (Eklund et al. 1974). These domains are separated by a deep cleft. The coenzyme-binding domain is composed of residues 176-318 and has a folding structure 

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