MICROBODIES
Single unit membrane bound small spherical structures.
Microbodies are structurally related to lysosome.
On the basis of functions microbodies are of four types-
1. Peroxisomes or Uricosomes -
Discovered by Rhodin and Tolbert. Urate oxidase, Amino acid oxidase, Hydroxy acid Oxidase, Peroxidase, Catalase enzymes occurs in it. Catalase has 2nd fastest enzyme activity whereas carbonic anhydrase enzyme has fastest enzyme activity. In animal cells peroxisomes concerned with peroxide metabolism. Urate oxidase, Amino acid oxidase and peroxidase catalyse the oxidation of amino acids producing H2O . Catalase degrade the H2O into water and oxygen. In plants, peroxisomes occur in cells of green tissues and concerned with photorespiration (glycolate pathway). Peroxisomes also involved in b-oxidation of fatty acids.
2. Glyoxysomes -
Discovered by Rhodin, Beever and Briedenbach. Glyoxysomes occur only in plants especially in fatty seeds, guard cells of stomata and unripe fruits. Glyoxylic acid cycle takes place in Glyoxysome. This cycle was discoverd by Kreb and Kornberg and is a variant of Kreb's cycle. Glyoxylic acid cyle is Amphibolic (i.e. it may be anabolic or catabolic), due to this cycle stomata are closed in night. Glyoxysomes contain a-hydroxy acid and b- hydroxy acid enzymes.
Significance of Glyoxylic acid cycle
(a) The cycle is involved in the formation of different organic acid during ripening of fruits.
(b) This cycle converts fats into carbohydrates during germination of fatty seeds.
(c) This cycle may convert organic acids in carbohydrates ( concerned with mechanism of closing of stomata during night).
(d) Glyoxylate is precursor of two amino acids, glycine and serine.
In addition to enzymes for glyoxylate cycle, the glyoxysomes also contain catalase and H20 generating glycolic oxidase. Therefore Glyoxysomes are considered as a highly specialised peroxisomes.
3. Transosome -
Discovered by Press in ovary follicle cells of birds. It has tripple unit membranes. It helps in yolk synthesis during vitellogenesis. Reserve food of ovum is called yolk.
4. Lomasome -
Discovered by Moore and McAlear. These are found in fungi. These are present between cell wall and plasma membrane. Lomasome helps in formation of septum during cell division.