Human Seminal Plasma Soluble 5′-Nucleotidase: Regulatory Aspects of the Dephosphorylation of Nucleoside 5′-Monophosphates

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 2,3bisphosphate, 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 Ap₅A. 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.