STRUCTURE-FUNCTION RELATIONSHIPS IN OSTEOCLAST 511 



identified with Ivsosomes, the carriers of hvdrolvtic enzvmes in 

 Other cells ( de Man et al, 1960; Holt and Hicks, 1961 ) , are not to 

 be seen in the osteoclast. On the other hand, as the electron micro- 

 graphs show, the cytoplasm of this cell is characteristically packed 

 with small vesicles bounded by a single membrane. It is natm-ally 

 tempting to think of these as the carriers of the enzyme cocktail 

 needed for solubilization of the collagen and the ground substance. 

 They might be a form of, or related to, "lysosomes," or "phago- 

 somes" (de Duve, 1959; Novikofl:", 1960), or "cytolysomes" (Novi- 

 koff and Essner, 1962). Perhaps they empty into the cytoplasmic 

 folds, much as "dense bodies" believed to contain hydrolytic en- 

 zymes have been thought to coalesce with liver cell vacuoles (de 

 Man et al., 1960). Rose (1957), of course, has watched small dark 

 cytoplasmic bodies moving toward and fusing with pinosomes in 

 living cells and has proposed that this may represent enzyme trans- 

 fer. 



It is very unfortunate that little or nothing is known about the 

 cytochemistry of the osteoclast at the electron microscope level. 

 However, there is quite a lot of information from the light micro- 

 scope, and osteoclasts are known to contain a wide range of enzymes. 

 Leaving aside their oxidases, dehydrogenases (Walker, 1961; Bur- 

 stone, 1960/^), and carbonic anhydrase (Simasaki and Yagi, 1960), 

 they possess acid phosphatase (Burstone, 1960rt, 1960c,- Changus, 

 1957), leucine aminopeptidase (Burstone, 1960«,- Lipp, 1959), and 

 Q:,^-glycosidase and galactosidase (Schlager, 1959, 1960). Such 

 enzymes are often considered to be involved in the breakdown of 

 soft tissue constituents elsewhere in the body ( de Duve, 1959; Novi- 

 koff, 1960; Cabrini, 1961), and there seems no reason why they 

 should not have a similar efi^ect on bone matrix once decalcified. 



Cytochemical observations made in our laboratory (Hancox and 

 Warner, unpublished) on whole osteoclasts in tissue culture have 

 provided some suggestive results. The advantage of these over sec- 

 tioned cells is that cytological detail is very much better preserved. 

 Thus far, acid phosphatase, leucine aminopeptidase, and yS-glucuron- 

 idase have been studied. The reaction product is located in the cyto- 

 plasm in the form of droplets and granules whose size and number 

 seem to coincide quite well with those of the larger vesicles seen 



