Some Remarks and Questions on Metabolic Patterns in the Family of Bone Cells 13 



worked with long bones of 4-week-old mice; Herrmann-Erlee with 15 day-old 

 mouse radius rudiments. In reproducing their semi-quantitative data I restrict myself 

 to some data concerning the carbohydrate metabolism of the cells of the inner 

 periosteum and the osteoblasts, the osteocytes and the osteoclasts. Taking together 

 data from both authors and omitting a number of minor discrepancies they demon- 

 strate from each of the main pathways a number of enzymes to be active. However 

 it is quite remarkable that they observed no 6-p-G Dehydrogenase activity as this is 

 the second enzyme in the pentose phosphate cycle of which the initial enzyme, the 

 G-6-p Dehydrogenase, was found to be active. The data of Balogh show in fact dis- 

 appointingly little difference between the different types of cells. However Herr- 

 mann-Erlee finds Succinic dehydrogenase to be active only in the osteoclasts and 

 osteoblasts at the ossification ring. In Balogh's data the osteoclasts do not hold a 

 monopoly, but here this enzyme is more active than in the other types of cells. 

 Moreover and in sharp contradistinction to Balogh, she finds no Lactic dehydro- 

 genase in osteoclasts. Finally she was unable to demonstrate a-glycerophosphate 

 dehydrogenase activity in the cell types mentioned, with the only exception again of 

 the osteoblasts at the ossification ring. 



Summarizing, no convincing argument is found to doubt the completeness of the 

 carbohydrate metabolizing machinery. Moreover the osteoclasts and the osteoblasts at 

 the diaphyseal-metaphyseal junction seem to keep a special position. However the 

 data are absolutely insufficient to construe different metabolic patterns in the sense I 

 have defined. Concerning the special position of the osteoclasts I would like to add 

 another point: Both authors found the osteoclasts deprived of Glutamic Dehydro- 

 genase activity, and as you know this enzyme belongs to the domain of protein 

 catabolism. 



Before passing on to some investigations concerning metabolic pathways in bone 

 cells it will repay to discuss, whether essential cellular potencies must find by necessity 

 some reflection in the conditions of the metabolic pathways. I will try to formulate 

 an answer on the basis of a special example: In the Liege symposium we have heard 

 Vaes's paper on acid Hydrolases and Lysosomes in bone cells (Vaes, 1965). Moreover 

 in Leyden we have seen his successfull work on the PTE intensified release of Lyso- 

 somal enzymes from cultivated mouse calvaria. I will take the position that in all 

 probability his finding will prove to be of essential importance in the understanding 

 of the process of bone resorption. Now one cannot foresee that the intracellular 

 presence of even a high number of Lysosomes can be read in some way or another 

 from certain peculiarities in the metabolic pathways. However it is possible that the 

 production of the acid hydrolases and of the organic acids, necessary to bring 

 the released enzymes in their pH optimum, or even the mechanism of extrusion, do ask 

 for certain provisions that indeed can be read from the pathways. My answer then is, 

 that perhaps many peculiarities in the metabolic pathways of bone cells will become 

 explainable, provided data from other origins become available. 



With only a few exceptions data concerning the main metabolic routes in bone 

 tissue are not specific to the different types of cells; on the contrary they mostly 

 reflect the combined contribution of different types. 



In his thesis "Bone metabolism and the action of Parathyroid extract" Hekkel- 

 MAN gave us an excellent survey, describing the 1963 situation. Leaving out some im- 

 portant controversial points in the literature, we meet a picture in which 1. the glyco- 



