homolactic

Homolactic fermentation, also known as homofermentative lactic acid fermentation, is a form of lactic acid fermentation in which the principal end product from glucose is lactate (lactic acid). It is characteristic of certain lactic acid bacteria and is distinguished from heterolactic fermentation, which yields lactate along with other products such as ethanol, acetate, or carbon dioxide.

Biochemistry and pathway: During glycolysis, one molecule of glucose is converted to two molecules of pyruvate. In homolactic fermentation, pyruvate is reduced to lactate by the enzyme lactate dehydrogenase, using NADH and regenerating NAD+ for continued glycolysis. The overall result is the conversion of glucose to two lactate molecules, with glycolysis providing a net gain of two ATP per glucose and no substantial production of other end products. The NAD+/NADH balance is maintained by the reduction of pyruvate to lactate.

Organisms and contexts: Homofermentative lactic acid bacteria, including many strains of Streptococcus, Lactococcus, and some Lactobacillus species, perform homolactic fermentation. These organisms are widely used in dairy and other fermentations, producing a clean lactate-dominated product. In animal physiology, skeletal muscle under anaerobic conditions also converts pyruvate to lactate to regenerate NAD+, enabling continued ATP production through glycolysis; this is commonly described as a homolactic process in muscle energy metabolism.

Distinctions and applications: Homolactic fermentation yields primarily lactate, unlike heterolactic fermentation, which generates a mixture of lactate and other metabolites. It is harnessed industrially in the production of fermented dairy products (such as yogurt and certain cheeses) and in various fermentation processes where a rapid, lactate-rich end product is desired.