calciumindependent

Calcium-independent, often written as calcium-independent, is a descriptor used in biochemistry and cell biology to denote enzymes, signaling proteins, or pathways that do not require calcium ions (Ca2+) for their catalytic activity or regulatory function. This contrasts with calcium-dependent components that rely on Ca2+ as a cofactor or signaling trigger. The term is commonly applied to specific enzymes and signaling proteins rather than to whole cells.

A canonical example is calcium-independent phospholipase A2 (iPLA2), an enzyme that hydrolyzes phospholipids without the need for Ca2+. iPLA2 enzymes participate in membrane remodeling, lipid signaling, and inflammatory processes and are regulated by factors other than Ca2+, such as ATP or redox state in some contexts. In signaling pathways, several protein kinase C (PKC) isoforms are described as calcium-independent. Novel PKCs (for example, PKCδ, PKCε, PKCη) respond to diacylglycerol and phospholipids without requiring Ca2+, while atypical PKCs (PKCζ, PKCι/λ) are largely independent of Ca2+ and DAG.

In research, determining calcium-dependence involves manipulating Ca2+ availability—such as using calcium chelators or Ca2+-free buffers—to see whether activity persists. The calcium-independent designation helps distinguish mechanisms that can operate in environments with limited or tightly buffered Ca2+ from those that require Ca2+ signaling.

See also: calcium-dependent, calcium signaling, phospholipase A2.