Inorganic pyrophosphate-phosphohydrolytic activity in human serum. Catalytic properties of the ionic species of PPi and MgPPi complexes

Mogens Hørder*

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Abstrakt

The kinetics of the enzyme-catalyzed hydrolysis of inorganic pyrophosphate (PPi) by human serum has been investigated as a function of the ionic species of PPi and Mg at pH 9.0 (37 °C): Mg2+, MgPPi 2-, and PPi 4-. Hyperbolic activity-substrate curves are obtained when MgPPi 2- and PPi 4t- are used as substrates; the activity substrate curve for total PPi is sigmoid. On the basis of experiments in which MgPPi 2- and PPi 4- are assumed to be alternative substrates for the same site, a catalytic mechanism is proposed: PPi 4- is the real substrate; Mg2+ does not directly modify the binding or the hydrolysis of PPi 4-, but leads to a decrease in the activity through formation of MgPPi complexes. Neither Mg2- nor MgPPi complexes bind to the enzyme.

OriginalsprogEngelsk
BogserieBBA - Enzymology
Vol/bind321
Udgave nummer1
Sider (fra-til)329-335
Antal sider7
ISSN0005-2744
DOI
StatusUdgivet - 15. sep. 1973

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