Human placental (Asymmetrical) diadenosine 5',5'''-P1,P4-tetraphosphate hydrolase: purification to homogeneity and some properties.

The diadenosine 5',5'''-P1,P4-tetraphosphate (asymmetrical) hydrolase (EC 3.6.1.17) from human placenta has been purified to homogeneity by ammonium sulfate fractionation, ion-exchange chromatography on DEAE-Sephacel, gel filtration on Sephadex G-100, and affinity elution from red Sepharose. The enzyme is a single polypeptide of M(r) 19,200. It exhibits maximum (100%) activity at pH 7.3 in the presence of 3 mM MgCl2 and 60, 50, and 40% of the activity in 1 mM CoCl2, 0.1 mM ZnCl2, and 0.5 mM MnCl2, respectively. The Km value calculated for diadenosine tetraphosphate in the presence of Mg2+ is 10 microM and in the presence of Zn2+ 40 microM. Adenosine 5'-tetraphosphate, guanosine 5'-tetraphosphate, and fluoride proved to be inhibitors of the diadenosine tetraphosphate hydrolase; the I50 values were 6, 10, and 20 microM, respectively. Diguanosine tetraphosphate, bis-2,6-diaminopurine beta-D-ribofuranoside tetraphosphate, and diadenosine pentaphosphate were substrates for the hydrolase; relative velocities of hydrolysis estimated for 0.5 mM diadenosine tetraphosphate and these other substrates were 1:0.51:0.44:0.20, respectively. Diadenosine tetraphosphate analogues with P2-P3 bridges such as -CF2-, -CCl2-, and -CH2- were hydrolyzed to adenosine 5'-phosphate and the corresponding adenosine 5'-triphosphate analogue.(ABSTRACT TRUNCATED AT 250 WORDS)