PEROXISOMES AND GLYOXYSOMES
Certain small ovoid unit membrane bound sac like cytoplasmic organelles, resembling lysosomes in size and appearance were isolated from various types of animals and plant cells by due Duve 1965 these however differ from lysosomes in being formed by budding from smooth endoplasmic reticulum and containing not hydrolysing but mainly certain oxidative enzyme oxidases. D amino acid oxidase and urate oxidase .These enzyme catalyse oxidation of amino uric and lactic acids to synthesize hydrogen peroxide (H2O2) and catalase enzyme which decomposes H2O2 .That is why these organelles were christened peroxisomes probably these correspond to microbodies detected carlier 1954 Rhodin by electron microscopy. Later it was found that some peroxisomal enzyme are related to the biosynthesis of certain components of cellular membranes .In plant cells peroxisomes co operate with chloroplasts in the process of photo respiration.
The number of peroxisomes per cell varies from 70 to100. How and where these are formed in the cells is not yet clearly understood. Possibly , these form as buds from cytoplasmic reticulum but their enzyme are synthesized by ribosomes found free in the cytosol peroxisomes have brief life span of 5 to6 days .Hence, old ones are regularly dissolved by autophagy and new ones are formed.
Glyoxysomes : are organelles similar to peroxisomes but contain enzyme of glyoxylate cycle which is concerned with conversion of fats to sugars. These occur in cells of fungi, some protista and germinating seeds.