guanosine-monophosphate and diadenosine-tetraphosphate

Human seminal plasma contains two enzyme activities both capable of dephosphorylating all nucleoside 5-monophosphates with different efficiency and specificity. Broad-spectrum soluble 5'-nucleotidase is the object of this paper which deals with the definition of the response of this enzyme to effectors, some physiological and others not naturally occurring. The enzyme did not show any product regulation as all the nucleosides tested caused a moderate effect on the hydrolysis of the substrates. Theophylline and other xanthine derivatives had no effect on enzyme activity, whereas glycerate 2,3-bisphosphate, like other soluble 5'-nucleotidases, caused a stimulation of the enzyme, especially toward CMP and UMP. 5-Deoxy-5-isobutylthiadenosine resulted in no inhibition of the hydrolysis of AMP and IMP. The enzyme was affected neither by monovanadate nor by decavanadate, whereas it was strongly inhibited by Ap5 A. Variations in adenylate energy charge did not cause any alteration of the enzyme activity toward AMP and only a slight decrease of the hydrolysis of IMP. These regulatory properties, distinct from those of other soluble 5'-nucleotidases, show that this form, newly isolated from human seminal plasma, is subject to an almost unique, tissue-specific regulation.

Topics: 5'-Nucleotidase; Adenosine Monophosphate; Cytidine Monophosphate; Dinucleoside Phosphates; Energy Metabolism; Guanosine Monophosphate; Humans; Inosine Monophosphate; Male; Phosphorylation; Purine Nucleotides; Semen; Solubility; Uridine Monophosphate; Vanadates

The rate of hydrolysis of IMP (0.5 mM) by cytosol 5'-nucleotidase from Artemia embryos was increased up to 7-fold by concentrations of around 10 microM diadenosine tetraphosphate (Ap4A). Half maximal activation of the enzyme was accomplished with 5 microM Ap4A. The Km (S 0.5) values of the nucleotidase for IMP, GMP, AMP, XMP and CMP decreased about 10 fold in the presence of 10 microM Ap4A. Maximum velocity of the enzyme was not affected by Ap4A. ATP had been previously described as an activator of the enzyme. However, comparatively with Ap4A, concentrations of ATP two orders of magnitude higher are needed to elicit similar effects on the enzyme. Preliminary results indicate that Ap4A is also an activator of the cytosol 5'-nucleotidase from rat liver.

Topics: 5'-Nucleotidase; Adenine Nucleotides; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Artemia; Cytidine Monophosphate; Cytosol; Dinucleoside Phosphates; Guanosine Monophosphate; Inosine Monophosphate; Kinetics; Nucleotidases; Rats; Ribonucleotides; Xanthine