Researchers Identify Soluble Adenylyl Cyclase as a Crucial pH Sensor Regulating Sea Urchin and Salmon Sperm Motility

New research reveals sea urchin and salmon sperm rely on pH sensing enzymes for movement, highlighting new risks from ocean acidification in 2026.

By: AXL Media

Published: Feb 23, 2026, 11:15 AM EST

Source: The information in this article was sourced from Phys.org

Divergent Signaling Pathways in Aquatic Reproductive Biology

The fundamental mechanics of reproduction in the marine environment have long been a subject of intense scientific scrutiny, particularly concerning how microscopic cells navigate vast oceanic distances. New research published in February 2026 has unveiled a significant distinction between the fertility triggers of mammals and those of aquatic species such as sea urchins and salmon. While it was previously assumed that a specific chemical mechanism was universal across all sexually reproducing animals, this investigation proves that marine organisms have evolved unique sensory pathways. According to Benjamin Kaupp, an emeritus director at the Max Planck Institute, the concentration of bicarbonate in seawater is significantly lower than in mammalian environments, making old theories regarding its role in fish and invertebrates implausible.

The Enzymatic Sentinel of Intracellular Alkalinity

At the center of this biological discovery is a protein known as soluble adenylyl cyclase, or sAC. This enzyme is responsible for producing cAMP, a critical messenger substance that provides the chemical energy required for a sperm cell’s tail to beat. In humans and other mammals, sAC is activated when it encounters high concentrations of bicarbonate in the reproductive tract. However, the study conducted by researchers at the University of Bonn has demonstrated that in sea urchins and salmon, sAC functions as a direct pH sensor. According to report details, the enzyme lacks the specific amino acids required to respond to bicarbonate, instead reacting directly to the alkalinity of the surrounding fluid to initiate motility.

Chemical Gradients and the Mechanics of Underwater Navigation

The transition from a state of total immobility to active swimming is a high stakes event for the survival of marine species. According to Olivia Kendall, a doctoral student at the University of Bonn, sperm remain completely immotile while stored in the testis and only become active following the act of ejaculation. Once released into the water, the internal pH of the sperm cell rises, becoming more alkaline and activating the sAC enzyme to produce cAMP. This process is further amplified when the sperm detects attractants released by the egg, which triggers a second rise in pH. This two stage activation allows the sperm to not o...