Zinc dimeric metalloenzymes

The alkaline phosphatase from E. coli is a zinc-containing metalloenzyme comprising two identical subunits. Different groups have claimed that varying numbers of zinc atoms are present in the dimer, but it has recently been demonstrated that there are four, of which only two appear to... 

A wide variety of papers dealing with P-NMR studies of the dimeric enzyme (MW 94,000) purified from Escherichia coli have been reported, and two comprehensive reviews are available (Coleman and Chlebowski, 1979 Coleman et al, 1979). The enzyme catalyzes the nonspecific hydrolysis of phosphomonoesters, and it is widely accepted that a covalent phos-phoserine intermediate (E-P) and a noncovalent E P complex play an important role in catalysis (Reid and Wilson, 1971). The enzyme is normally purified as a zinc(II) metalloenzyme, but the metal ion can be removed and replaced with cadmium, cobalt, copper, or manganese, giving rise to enzymes with different properties. Such species have been used to advantage for various q>ectroscopic studies including P-NMR experiments. 

All forms of human ADH are dimeric zinc-metalloenzymes comprised of subunits with molecular masses of approximately 40,000, and are located in the cytoplasm. The different ADH isozymes are grouped into five classes based on their... 

Superoxide dismutase enzymes are functional dimers of molecular weight (Mr) of approximately 32 kDa. The enzymes contain one copper ion and one zinc ion per subunit. Superoxide dismutase (SOD) metalloenzymes function to disproportionate the biologically harmful superoxide ion-radical according to the following reaction ... 

Alkaline phosphatase160-164 is a dimeric zinc metalloenzym composed of two identical subunits. The number of zinc atoms per protein molecule varies in different preparations. However, only two seem to be required for catalytic activity. The molecular weight of the monomer has been reported to be 42.000 so the natural dimer would be twice that value. Alkaline phosphatase is a phosphorylating enzyme and has 760 residues per dimer. 

All of the human alcohol dehydrogenases are dimeric zinc metalloenzymes existing in multiple forms that may be homo- or heterodimers with subunits of aproxi-mately 40,000 daltons. Five classes exist in humans and their distribution varies... 

Alkaline phosphatases are typically dimeric zinc metalloenzymes ranging in size from 80 to 145 kDa. They catalyze a nonspecific phosphomonoesterase reaction of the following type ... 

Metalloenzyme-catalyzed phosphoric ester hydrolysis can be illustrated by alkaline phosphatase, by far the most-investigated enzyme of this class. The protein is a dimer of 94 kDa containing two zinc(II) and one magnesium(II) ions per monomer, and catalyzes, rather unspecifically, the hydrolysis of a variety of phosphate monoesters as well as transphosphorylation reactions. The x-ray structure at 2.8 A resolution obtained on a derivative in which all the native metal ions were replaced by cadmium(II) reveals three metals in each subunit. 

OPH catalyzes the hydrolysis of organophosphonates with P-0, P-F, P-S, and P-CN phosphoryl bonds such as those of coumaphos, sarin, VX, and paraoxon. Hydrolysis is facilitated by two metal atoms in the active site and results in the release of two protons (79). In the native dimeric form of the enzyme, zinc is coordinated to histidine residues in the active site. Reconstitution of the apo-entyme with cobalt or cadmium results in higher enzymatic activity than that observed in the zinc-metalloenzyme (20). 

Escherichia coli alkaline phosphatase, a dimeric zinc metalloenzyme ( 95,500 Da), binds 2 Zn ions and 1 Mg ion per monomer and functions in the non-specific hydrolysis of phosphate monoester. NMR (mi labeled histidine biosyntheti-cally incorporated into AP in conjunction with substrate NMR and Cd NMR methods were used for the assigmnent of the three Cd resonances to specific sites per monomer and their role in substrate binding. A full account of these studies can be found in the following references [6,25,80,82,201],... 

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