Biomaterial Database

mu-Monothiopyrophosphate as a substrate for inorganic pyrophosphatase and UDP-glucose pyrophosphorylase. 1996

E S Lightcap, and P A Frey

Institute for Enzyme Research, The Graduate School, University of Wisconsin-Madison, 53705, USA.

mu-Monothiopyrophosphate (MTP, (2-)O3P-S-PO3(-2)) is an excellent substrate for inorganic pyrophosphatase. The maximum velocity for the hydrolysis of MgMTP by inorganic pyrophosphatase is 24% of that for MgPPi at pH 8.0 and 5 degrees C and 190% at pH 9.0 and 15 degrees C. The hydrolyses of MnMTP and CoMTP proceed at 24 and > or = 7%, respectively, of the maximum velocity for the reaction of MgMTP at pH 8 and 5 degrees C. The maximum velocities for hydrolyses of MnPPi and CoPPi are 31 and 13% of that for MgPPi, respectively. There is no evidence that Mn2+ or Co2+ coordinate with bridging sulfur in MTP in such a way as to affect the rate of hydrolysis. The apparent Michaelis constants at pH 8 and 5 degrees C in the presence of 195 microM divalent metal ion are as follows: MgPPi, 12 microM; MnPPi, 19 microM; CoPPi, 12 microM; MgMTP, 45 microM; MnMTP, 5.3 microM; and CoMTP, 16 microM. The apparent Michaelis constants at pH 9 and 15 degrees C in the presence of 10 mM divalent metal ion are MgPPi, 1.9 microM and MgMTP, 19.1 microM. The values of kcat for MgPPi at pH 8 and 5 degrees C and at pH 9 and 15 degrees C are 8 s(-1) and 12.4 s(-1), respectively. The values of kcat for MgMTP under the same conditions are 2 s(-1) and 24 s(-1), respectively. MTP and MgMTP undergo nonenzymatic hydrolysis by a mechanism in which monomeric metaphosphate monoanion (PO3) is a discrete intermediate (Lightcap, E.S., and Frey, P.A. (1992) J. Am. Chem. Soc. 114, 9750-9755). This reaction is accommodated at the active site of inorganic pyrophosphatase, indicating that the mechanism of enzymatic hydrolysis is dissociative. MgMTP is also a substrate for UDP-glucose pyrophosphorylase, reacting at 4.8% of the maximum velocity of MgPPi and with a Michaelis constant 17 times larger than that for MgPPi. The P-S bonds of MgMTP are not cleaved in the pyrophosphorylase reaction, but the product UTP beta gamma S is chemically unstable and undergoes hydrolysis to UDP beta S and Pi, making the cleavage of UDP-glucose to glucose-1-P, UDP beta S and Pi, experimentally irreversible.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008345	Manganese	A trace element with atomic symbol Mn, atomic number 25, and atomic weight 54.94. It is concentrated in cell mitochondria, mostly in the pituitary gland, liver, pancreas, kidney, and bone, influences the synthesis of mucopolysaccharides, stimulates hepatic synthesis of cholesterol and fatty acids, and is a cofactor in many enzymes, including arginase and alkaline phosphatase in the liver. (From AMA Drug Evaluations Annual 1992, p2035)
D008956	Models, Chemical	Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.	Chemical Models,Chemical Model,Model, Chemical
D011755	Pyrophosphatases	A group of enzymes within the class EC 3.6.1.- that catalyze the hydrolysis of diphosphate bonds, chiefly in nucleoside di- and triphosphates. They may liberate either a mono- or diphosphate. EC 3.6.1.-.	Pyrophosphatase
D011756	Diphosphates	Inorganic salts of phosphoric acid that contain two phosphate groups.	Diphosphate,Pyrophosphate Analog,Pyrophosphates,Pyrophosphate Analogs,Analog, Pyrophosphate
D002413	Cations, Divalent	Positively charged atoms, radicals or groups of atoms with a valence of plus 2, which travel to the cathode or negative pole during electrolysis.	Divalent Cations
D003035	Cobalt	A trace element that is a component of vitamin B12. It has the atomic symbol Co, atomic number 27, and atomic weight 58.93. It is used in nuclear weapons, alloys, and pigments. Deficiency in animals leads to anemia; its excess in humans can lead to erythrocytosis.	Cobalt-59,Cobalt 59
D005957	UTP-Glucose-1-Phosphate Uridylyltransferase	An enzyme that catalyzes the formation of UDPglucose from UTP plus glucose 1-phosphate. EC 2.7.7.9.	Glucosephosphate Uridylyltransferase,UDP Glucose Pyrophosphorylase,UDPG Pyrophosphorylase,Pyrophosphorylase, UDP Glucose,Pyrophosphorylase, UDPG,UTP Glucose 1 Phosphate Uridylyltransferase,Uridylyltransferase, Glucosephosphate,Uridylyltransferase, UTP-Glucose-1-Phosphate
D000998	Antiviral Agents	Agents used in the prophylaxis or therapy of VIRUS DISEASES. Some of the ways they may act include preventing viral replication by inhibiting viral DNA polymerase; binding to specific cell-surface receptors and inhibiting viral penetration or uncoating; inhibiting viral protein synthesis; or blocking late stages of virus assembly.	Antiviral,Antiviral Agent,Antiviral Drug,Antivirals,Antiviral Drugs,Agent, Antiviral,Agents, Antiviral,Drug, Antiviral,Drugs, Antiviral
D012441	Saccharomyces cerevisiae	A species of the genus SACCHAROMYCES, family Saccharomycetaceae, order Saccharomycetales, known as "baker's" or "brewer's" yeast. The dried form is used as a dietary supplement.	Baker's Yeast,Brewer's Yeast,Candida robusta,S. cerevisiae,Saccharomyces capensis,Saccharomyces italicus,Saccharomyces oviformis,Saccharomyces uvarum var. melibiosus,Yeast, Baker's,Yeast, Brewer's,Baker Yeast,S cerevisiae,Baker's Yeasts,Yeast, Baker