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Acid Hydrolases, Lysosomes and Bone Resorption Induced by 

 Parathyroid Hormone 



G. Vaes 

 Laboratoire de Chimle Physiologique, Universite de Louvain, Louvain, Belgique. 



As pointed out elsewhere (Vaes, 1965; Vaes and Jacques, in press a), both 

 mineral and organic matrix seem to be removed almost simultaneously in the process 

 of bone resorption. Since organic acids produced and secreted by bone cells are 

 thought to be the agents of the solubilization of bone mineral, the simultaneous 

 hydrolysis of the organic matrix presumably occurs at an acid pH: the possibility 

 that the acid hydrolases of bone cells may play a role In the digestion of the organic 

 matrix was, therefore, considered. 



So far, nine acid hydrolases have been demonstrated In homogenates of newborn 

 rat calvaria (Vaes and Jacques, in press a): /^-glucuronidase, /?-N-acetylaminodeoxy- 

 glucosldase, acid deoxyribonuclease, acid ribonuclease, acId-/S-glycerophosphatase and 

 acid phenylphosphatase showing optimal activity around pH5; cathepsin, /5-galac- 

 tosldase and hyaluronldase with an optimum around pH 3.6. The first eight hydro- 

 lases, and probably also hyaluronldase (Vaes, in preparation), have been shown by 

 means of tissue fractionation techniques to be associated with a special group of 

 cytoplasmic particles distinct both from mitochondria and from microsomes and 

 similar to liver lysosomes (Vaes and Jacques, in press b). The acid hydrolases 

 studied are largely latent in fresh untreated homogenates; they are released in a 



