Bacterial family II pyrophosphatases (PPases) are homodimeric enzymes,
with the active site located between two catalytic domains. Some family
II PPases additionally contain regulatory cystathionine β-synthase (CBS)
domains and exhibit positive kinetic cooperativity, which is lost upon
CBS domain removal. We report here that CBS domain-deficient family II
PPases of Bacillus subtilis and Streptococcus gordonii
also exhibit positive kinetic cooperativity, manifested as an up to a
five-fold difference in the Michaelis constants for two active sites. An
Asn79Ser replacement in S. gordonii PPase preserved its
dimeric structure but abolished cooperativity. The results of our study
indicated that kinetic cooperativity is an inherent property of all
family II PPase types, is not induced by CBS domains, and is sensitive
to minor structural changes. These findings may have inferences for
other CBS-proteins, which include important enzymes and membrane
transporters associated with hereditary diseases.