Autolysis (biology)
   HOME

TheInfoList



OR:

In
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, autolysis, more commonly known as self-digestion, refers to the destruction of a
cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
through the action of its own
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
s. It may also refer to the digestion of an enzyme by another molecule of the same enzyme. The term derives from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
αὐτο- ("self") and λύσις ("splitting").


Biochemical mechanisms of cell destruction

Autolysis is uncommon in living adult organisms and usually occurs in
necrotic Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...
tissue as enzymes act on components of the cell that would not normally serve as substrates. These enzymes are released due to the cessation of active processes in the cell that provide substrates in healthy, living tissue; autolysis in itself is not an active process. In other words, though autolysis resembles the active process of digestion of nutrients by live cells, the dead cells are not actively digesting themselves as is often claimed, and as the synonym self-digestion suggests. Failure of respiration and subsequent failure of
oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine tri ...
is the trigger of the autolytic process. The reduced availability and subsequent absence of high-energy molecules that are required to maintain the integrity of the cell and maintain homeostasis causes significant changes in the biochemical operation of the cell. Molecular oxygen serves as the terminal electron acceptor in the series of biochemical reactions known as oxidative phosphorylation that are ultimately responsible for the synthesis of
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of ...
, the main source of energy for otherwise thermodynamically unfavorable cellular processes. Failure of delivery of molecular oxygen to cells results in a metabolic shift to anaerobic
glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...
, in which glucose is converted to pyruvate as an inefficient means of generating adenosine triphosphate. Glycolysis has a lower ATP yield than oxidative phosphorylation and generates acidic byproducts that decrease the pH of the cell, which enables many of the enzymatic processes involved in autolysis. Limited synthesis of adenosine triphosphate impairs many cellular transport mechanisms that utilize ATP to drive energetically unfavorable processes that transport ions and molecules across the cellular membrane. For example, the
membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...
of the cell is maintained by the sodium-potassium ATPase pump. Failure of the pump results in loss of membrane potential as sodium ions accumulate within the cell and potassium ions are lost through ion channels. Loss of membrane potential encourages movement of calcium ions into the cell, followed by movement of water into the cell, as driven by osmotic pressure. Water retention, ionic changes, and acidification of the cell damages membrane-bound intracellular structures including the
lysosome A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prot ...
and
peroxisome A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen pero ...
.
Lysosome A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prot ...
s are membrane-bound organelles that typically contain a broad spectrum of enzymes capable of hydrolytic deconstruction of
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
s,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s,
nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...
s,
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
s, phosphoric acyl esters, and sulfates. This process requires compartmentalization and segregation of enzymes and substrates via a single intracellular membrane that prevents unwarranted destruction of other intracellular components. Under normal conditions, the molecular machinery of the cell is further protected from lysosomal enzyme activity by regulation of cytosolic pH. The activity of lysosomal
hydrolase Hydrolase is a class of enzyme that commonly perform as biochemical catalysts that use water to break a chemical bond, which typically results in dividing a larger molecule into smaller molecules. Some common examples of hydrolase enzymes are este ...
s is optimal at a moderately acidic pH of 5, which is significantly more acidic than the more basic average pH of 7.2 in the surrounding cytosol. However, the accumulation of products of glycolysis decreases the pH of the cell, reducing this protective effect. Furthermore, lysosomal membranes damaged by water retention in the cell will release lysosomal enzymes into the cytosol. These enzymes are likely to be active due to the decreased cytosolic pH and are thus free to utilize cellular components as substrates.
Peroxisome A peroxisome () is a membrane-bound organelle, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. Peroxisomes are oxidative organelles. Frequently, molecular oxygen serves as a co-substrate, from which hydrogen pero ...
s typically are responsible for the breakdown of lipids, particularly long-chain fatty acids. In the absence of an active electron transport chain and associated cellular processes, there is no metabolic partner for the reducing equivalents in the breakdown of lipids. In terms of autolysis, peroxisomes provide catabolic potential for fatty acids and reactive oxygen species, which are released into the cytosol as the peroxisomal membrane is damaged by water retention and digestion by other catabolic enzymes.


Use

The release of catabolically active enzymes from their sub-cellular locations initiates an irreversible process that results in the complete reduction of deceased organisms. Autolysis produces an acidic, anaerobic, nutrient-rich environment that nurtures the activity of invasive and opportunistic microorganisms in a process known as
putrefaction Putrefaction is the fifth stage of death, following pallor mortis, algor mortis, rigor mortis, and livor mortis. This process references the breaking down of a body of an animal, such as a human, post-mortem. In broad terms, it can be viewed ...
. Autolysis and putrefaction are the main processes responsible for the decomposition of remains. In the healing of wounds, autolytic debridement can be a helpful process, where the body breaks down and liquifies dead tissue so that it can be washed or carried away. Modern
wound dressing A dressing is a sterile pad or compress applied to a wound to promote healing and protect the wound from further harm. A dressing is designed to be in direct contact with the wound, as distinguished from a bandage, which is most often used to hol ...
s that help keep the wound moist can assist in this process. In the food industry, autolysis involves killing
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...
and encouraging breakdown of its cells by various enzymes. The resulting autolyzed yeast is used as a flavoring or flavor enhancer. For
yeast extract Yeast extracts consist of the cell contents of yeast without the cell walls; they are used as food additives or flavorings, or as nutrients for bacterial culture media. They are often used to create savory flavors and umami taste sensations, a ...
, when this process is triggered by the addition of
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
, it is known as plasmolysis. In
bread Bread is a staple food prepared from a dough of flour (usually wheat) and water, usually by baking. Throughout recorded history and around the world, it has been an important part of many cultures' diet. It is one of the oldest human-made f ...
baking, the term (or, more commonly, its French
cognate In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymology, etymological ancestor in a proto-language, common parent language. Because language c ...
''autolyse'') is described as a period of rest following initial mixing of flour and water, before other ingredients (such as salt and yeast) are added to the dough. Doing so makes the dough easier to shape and improves structure. The term was coined by French baking professor
Raymond Calvel Raymond Calvel (1913 – 30 August 2005) was a bread expert and professor of baking at ENSMIC in Paris, France. Calvel has been credited with creating a revival of French-style breadmaking, as well as developing an extensive body of research on ...
, who recommended the procedure as a means of reducing kneading time, thereby improving the flavor and color of bread. Calvel argues that long kneading times subject dough to atmospheric oxygen, which bleaches the naturally occurring
carotenoids Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, ...
in bread flour, robbing the flour of its natural creamy color and flavor. In the making of fermented beverages, autolysis can occur when the
must Must (from the Latin ''vinum mustum'', "young wine") is freshly crushed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace and typically makes up 7–23% of t ...
or
wort Wort () is the liquid extracted from the mashing process during the brewing of beer or whisky. Wort contains the sugars, the most important being maltose and maltotriose, that will be fermented by the brewing yeast to produce alcohol. Wort ...
is left on the lees for a long time. In
beer brewing Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer ...
, autolysis causes undesired off-flavors. Autolysis in winemaking is often undesirable, but in the case of the best Champagnes it is a vital component in creating flavor and mouth feel.J. Robinson (ed) ''The Oxford Companion to Wine'' Third Edition p. 54 Oxford University Press 2006


See also

*
Programmed cell death Programmed cell death (PCD; sometimes referred to as cellular suicide) is the death of a cell (biology), cell as a result of events inside of a cell, such as apoptosis or autophagy. PCD is carried out in a biological process, which usually confers ...
*
Post-mortem interval The post-mortem interval (PMI) is the time that has elapsed since an individual's death. When the time of death is not known, the interval may be estimated, and so an approximate time of death established. Postmortem interval estimations can ra ...
* Sub-lethal damage *
Vegemite Vegemite ( ) is a thick, dark brown Australian food spread made from leftover brewers' yeast extract with various vegetable and spice additives. It was developed by Cyril Callister in Melbourne, Victoria, in 1922. A spread for sandwiches, ...


References

{{Authority control Cellular processes Programmed cell death