Abstract
Lactate dehydrogenase(LDH)-containing vesicles were isolated from the matrix vesicle enriched fraction of the cultured osteoblast-like cells(MC3T3-E1). LDH actiyity was detected only in the presence of detergents, suggesting that NADH, the cofactor for the assay, does not penetrate the membrane of LDH-containing vesicles. In contrast, the activity of alkaline phosphatase, a marker enzyme of the matrix vecicles, was not detected in LDH-containing vesicles both in the presence and absence of detergent. These results show that LDH-containing vesicles are clearly differ from the matrix vesicles. The electrophoretic profiles of LDH isoenzymes from LDH-containing vesicles and the cytosolic LDH of the cell were nearly identical. On the other hand, other cytosolic enzymes were not detected in the vesicles. These results suggest the presence of mechanism for the specific up take of cytosolic LDH.
