Many prokaryotic soluble PPases (pyrophosphatases) contain a pair of regulatory adenine nucleotide-binding CBS (cystathionine β-synthase) domains that act as 'internal inhibitors' whose effect is modulated by nucleotide binding. Although such regulatory domains are found in important enzymes and transporters, the underlying regulatory mechanism has only begun to come into focus. We reported previously that CBS domains bind nucleotides co-operatively and induce positive kinetic co-operativity (non-Michaelian behaviour) in CBS-PPases (CBS domain-containing PPases). In the present study, we demonstrate that a homodimeric ehPPase (Ethanoligenens harbinense PPase) containing an inherent mutation in an otherwise conserved asparagine residue in a loop near the active site exhibits non-co-operative hydrolysis kinetics. A similar N312S substitution in 'co-operative' dhPPase (Desulfitobacterium hafniense PPase) abolished kinetic co-operativity while causing only minor effects on nucleotide-binding affinity and co-operativity. However, the substitution reversed the effect of diadenosine tetraphosphate, abolishing kinetic co-operativity in wild-type dhPPase, but restoring it in the variant dhPPase. A reverse serine-to-asparagine replacement restored kinetic co-operativity in ehPPase. Molecular dynamics simulations revealed that the asparagine substitution resulted in a change in the hydrogen-bonding pattern around the asparagine residue and the subunit interface, allowing greater flexibility at the subunit interface without a marked effect on the overall structure. These findings identify this asparagine residue as lying at the 'crossroads' of information paths connecting catalytic and regulatory domains within a subunit and catalytic sites between subunits.

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A segment of DNA encoding Succharomyces cerevisiae inorganic pyrophosphatase @pa gene) was amplified by the polymerase chain reaction. The pSCH1 and pSCB6 plasmids containing the ppa gene were obtained. Transformation of the E. coli BL21 strain with the resulting recombinant plasmids and selection of clones having extremely high expression of inorganic pyrophosphatase (PPase) were carried out. Superproduction of recombinant S. cerevisiue PPase up to 50% of the total bacterial protein was achieved. The enzyme was readily obtained and purified to homogeneity with the use of a simple purification technique. This work is the first description of S. cerevisiue PPase superproducer creation.