nonesterified

Nonesterified is a chemical descriptor meaning that a molecule is not bound by an ester linkage. The term is used in chemistry and biochemistry to distinguish free, or unesterified, forms from their esterified counterparts. Common usage includes nonesterified fatty acids and nonesterified cholesterol, though context often clarifies the exact meaning.

In physiology, nonesterified fatty acids (also called free fatty acids) are fatty acids released during lipolysis of triglycerides. They circulate in blood primarily bound to albumin, and can be taken up by liver and muscle for beta-oxidation or re-esterified. Their levels are hormonally regulated and can rise during fasting or stress; chronic elevation is associated with insulin resistance, obesity, and cardiovascular risk.

Nonesterified cholesterol: Free cholesterol refers to cholesterol not esterified with fatty acids. In plasma, cholesterol exists in both free and cholesteryl-ester forms; enzymes like LCAT convert free cholesterol to esters in lipoproteins. Free cholesterol is an essential component of cell membranes but in excess within lipoproteins or membranes can be deleterious. Lipoprotein particles carry both forms, with proportions varying by particle type.

Other uses: The descriptor nonesterified may apply to other molecules that can form esters, indicating the absence of ester bonds in the studied form; used to distinguish from esterified derivatives in analyses, synthesis, or metabolism.