Effects of spermine and spermidine on the inorganic pyrophosphatase of Streptococcus faecalis. Interactions between polyamines and inorganic pyrophosphate.
We have shown a dual role for Mg2+ in the hydrolysis of PPi catalysed by inorganic pyrophosphatase (PPase; EC 3.6.1.1) of Streptococcus faecalis; Mg2+ is necessary for the formation of the substrates, Mg1PPi2- and Mg2PPi0, and it also acts as an allosteric activator [Lahti + Jokinen (1985) Biochemistry 24, 3526-3530]. No activity can be observed with S. faecalis PPase in the absence of bivalent cations, which indicates that free PPi cannot serve as a substrate for this enzyme. However, significant activities were observed in the presence of spermine and spermidine, even though no bivalent cations were present. It was shown by particle-induced gamma-ray emission and particle-induced X-ray-emission analysis that the polyamines used were not contaminated with Mg2+ or any other bivalent cations that could support PPase activity. Hence it is obvious that polyamines are able to form a complex with PPi that serves as a substrate for PPase. The apparent stability constants for the 1:1 adducts of spermine and spermidine were estimated by a resin competition method. The values obtained at pH 7.5 were 2.7 X 10(3) M-1 and 6.4 X 10(2) M-1 respectively. Kinetic results further suggested that polyamines can also substitute for Mg2+ as an activator in vitro. The physiological significance of these polyamine effects were discussed.
Lahti
R
R
Department of Chemistry and Biochemistry, University of Turku, Finland.
Hannukainen
R
R
Lönnberg
H
H
D013293:Enterococcus faecalis / Q000201:enzymology*; D043564:Inorganic Pyrophosphatase; D008274:Magnesium / Q000378:metabolism; D011755:Pyrophosphatases / Q000378:metabolism*; D013095:Spermidine / Q000494:pharmacology*; D013096:Spermine / Q000494:pharmacology*
D013096:Spermine; D011755:Pyrophosphatases; D043564:Inorganic Pyrophosphatase; D008274:Magnesium; D013095:Spermidine