Protein Degeneration

PROTEIN DEGENERATION, a term used to designate those types of degeneration associated with local or general disorders in protein metabolism. The causes and essence of these disorders vary; the products appearing in cells and intercellular substance during these processes therefore differ in variety, although they always retain a protein character. In other words, the designation of protein degeneration unites a large group of processes with different etiologies and different morphological expressions. Unfortunately, further differentiation within this group presents great difficulties. Although we know the types to which the proteins of animal tissues belong (albumins, globulins, nucleoproteins, glycoproteins, albuminoids), nevertheless the detailed chemical structure of each of the numerous protein compounds entering into the composition of the organism under normal and pathological conditions has been studied far from sufficiently. Still less perfect is the ability to determine the nature of protein substances under the microscope using microchemical reactions. All this leads to the fact that there is still no scientific classification of protein degeneration, and the division currently accepted is based on a whole series of defining moments, such as: the gross similarity of products appearing in the tissue with various well-known substances (e.g., colloid degeneration from glue, amyloid from amylum-starch); the most striking external sign of the degenerated organ (e.g., cloudy swelling); the characteristic localization of changes (e.g., parenchymatous degeneration), etc. As for the essence of the process, as already indicated, it can be extremely diverse. In some cases, it apparently concerns the accumulation in the cell of a watery fluid containing a small amount of protein (vacuolar degeneration); in others, the swelling of certain structural parts of cells or intercellular substance, thanks to which they change their appearance and size, often becoming visible under conditions where they were previously indistinguishable (granular, hyaline degeneration); in third cases, the precipitation of certain protein substances due to a change in their solubility conditions, i.e., the transition of a sol into a gel (hyaline-droplet degeneration); in some forms there is a simple enhancement of a normal process (hyperkeratosis); sometimes, on the contrary, one can speak about the formation of a completely new pathological protein product uncharacteristic of normal tissue (amyloid degeneration). The combination of such heterogeneous phenomena into a single group must be recognized, of course, as largely conventional; as for the defining morphological features, only one remains common to all of them: the accumulation in the tissue of a protein substance either completely alien to it or uncharacteristic of it by place, time of appearance, or quantity. According to modern classification, the group of protein degenerations includes the following types: granular degeneration, or parenchymatous (also designated as cloudy swelling), vacuolar (or hydropic) degeneration (see), hyaline-droplet, mucous, colloid, hyaline, amyloid, and keratin (see). M. Skvortsov.