[Electron microscopic cytochemical study on lectin binding sites in the epiphyseal cartilage-plate of rabbit tibia]

Lectin is a common name given to a certain group of hemagglutinating proteins found primarily in plant seeds, which bind specifically to the branching sugar molecules of glycoproteins and glycolipids of the surface of the cells. The author selected 3 kinds of lectin among others. Those were concanavalin A (Con A) which specifically binds to the alpha-D-mannose, wheat germ agglutinin (WGA) which binds to N-acetyl glucosamine, and peanut agglutinin (PNA) which binds to beta-D-galactosamine. The localization of these lectins was examined in order to obtain any information on the process of the proteoglycan synthesis during the cellular differentiation in the epiphyseal cartilage-plate of the rabbit. The binding sites of Con A were determined by conjugating horse radish peroxidase as a marker in case of optical microscopic observations. For the purpose of electron microscopic observations, lectins were marked with gold colloidal particles. Most Con A was found in the rough surfaced endoplasmic reticulum, while a part of them was bound to the cis side of the Golgi apparatus. In the cellular column of the cartilage, Con A was increasingly abundant from the younger proliferating stage, through the maturing stage to the stage of hypertrophy, and diminished abruptly at the stage of provisional calcification. These observations were coincided with the degree of development of the endoplasmic reticulum during the maturation of cartilage cells. These findings suggest that alpha-D-mannose is indispensable to the initial stage of proteoglycan synthesis. WGA was observed from the cis side to the intermediate layer of Golgi apparatus, but not at the trans side of the Golgi apparatus, nor in the endoplasmic reticulum. These findings suggest that N-acetyl-glucosamine is an essential substance to the middle stage of proteoglycan synthesis. PNA was found within the nucleus and at the cis side of Golgi apparatus, but not in the endoplasmic reticulum nor in the secretion granules. This observation corroborates that beta-D-galactosamine is also essential to the middle stage of proteoglycan synthesis.