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Related Experiment Video

Updated: Jul 8, 2026

Medium-throughput Screening Assays for Assessment of Effects on Ca2+-Signaling and Acrosome Reaction in Human Sperm

Medium-throughput Screening Assays for Assessment of Effects on Ca²⁺-Signaling and Acrosome Reaction in Human Sperm

Published on: March 1, 2019

Sperm express a Ca2+-regulated NAADP synthase.

Sridhar R Vasudevan¹, Antony Galione, Grant C Churchill

¹Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.

The Biochemical Journal

|January 25, 2008

Summary

Scientists discovered a novel enzyme in sea urchin sperm that synthesizes nicotinic acid-adenine dinucleotide phosphate (NAADP). This enzyme shows physiologically relevant calcium regulation and specific nucleotide selectivity, unlike previously known enzymes.

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Measuring Intracellular Ca2+ Changes in Human Sperm using Four Techniques: Conventional Fluorometry, Stopped Flow Fluorometry, Flow Cytometry and Single Cell Imaging

Measuring Intracellular Ca²⁺ Changes in Human Sperm using Four Techniques: Conventional Fluorometry, Stopped Flow Fluorometry, Flow Cytometry and Single Cell Imaging

Published on: May 24, 2013

Area of Science:

Biochemistry
Cell Biology
Marine Biology

Background:

Nicotinic acid-adenine dinucleotide phosphate (NAADP) is a potent calcium (Ca2+) mobilizing second messenger.
Previously, NAADP synthesis was attributed to ADP-ribosyl cyclase enzymes, known for promiscuous activity and limited regulation.

Purpose of the Study:

To identify and characterize novel enzymes involved in NAADP synthesis.
To investigate the properties and regulation of a potential new NAADP-producing enzyme.

Main Methods:

Enzyme activity assays on sea urchin sperm surface preparations.
Characterization of substrate selectivity and Ca2+ dependency.
Analysis of enzyme products and catalytic activity.

Main Results:

A novel enzyme was identified on the sea urchin sperm surface.
This enzyme exhibits bell-shaped Ca2+ regulation within a physiologically relevant range (EC50 of 10 nM, IC50 of 50 microM).
The enzyme displays high selectivity for nucleotides with a 2'-phosphate group and demonstrates base-exchange activity, not cyclase activity.

Conclusions:

The identified enzyme represents the first true NAADP synthase.
Its unique properties suggest a more specific and physiologically relevant mechanism for NAADP production compared to ADP-ribosyl cyclases.