Some Remarks and Questions on Metabolic Patterns In the Family of Bone Cells 19 



every protein leaves the cell by the mechanism of reversed pinocytosis. However, taking 

 the rather generalized position that the cell has many "exits" allowing for a transport 

 even from the nuclear envelope through the endoplasmatic reticulum into the extra- 

 cellular space, again we meet a difficulty as the sites of protein synthetic action are 

 at "the other side", the ribosomal side, of the membranous screen. Although this all 

 belongs to elementary cytology it does not detain me from making the "moralizing" 

 statement that concepts concerning the specific protein synthetic activity of bone 

 cells need to take into account these problems of transport. This holds specially if we 

 are dealing with exogenous influences, such as the action of PTE, on these cellular 

 activities. 



In what I have said, I have tried to fulfil the promise of the title of my paper, 

 nothing more. However I do hope that you recognized that it was said in the voice 

 and with the special interest of a cellular biologist. 



References 



Balogh, K., Jr., H. R. Dudley, and R. B. Cohen: Oxidative enzyme activity in skeletal 



cartilage and bone. Lab. Invest. 10, 839 (1961). 

 CoHN, D. v., and F. D. Griffith: The influence of parathyroid extract on oxidative and 



decarboxylative pathways in bone. The parathyroid glands, ultra structure, secretion and 



function. Chicago: The University of Chicago Press 1965. 

 Gaillard, p. J.: The influence of parathormone on the explanted radius of albino mouse 



embryo's. Proc. kon. ned. Akad. Wet. C 63, 25 (1960). 



— The influence of parathyroid extract on the explanted radius of albino mouse embryo's. 

 II. Proc. kon. ned. Akad. Wet. C 64, 119 (1961). 



— Protein metabolism and the effect of parathyroid on bone. Texas reports on Biology and 

 Medicine Suppl. I, 23, 259 (1965). 



Hekkelman, J. W. : Bone metabolism and the action of parathyroid extract. Thesis. Leiden 

 1963. 



— An enzymological study of bone metabolism and its regulation by parathyroid hormone. 

 In Calcified Tissues. Richelle, L. J., and M. J. Dallmagne (eds.). Liege: Universlte de 

 Liege 1965, p. 393. 



Herrmann-Erlee, M. P. M.: A histochemical investigation of embryonic long bones: the 

 effect of parathyroid hormone on the activity of a number of enzymes. Proc. kon. ned. 

 Akad. Wet. C65, 22 (1962). 



Peck, W. A., S. J. Birge, and S. A. Fedak: Bone cells: Biochemical and biological studies 

 after enzymatic isolation. Science 146, 1476 (1964). 



Rasmussen, H., C. Arnaud, and C. Hawker: Actlnomycin D and the response to para- 

 thyroid hormone. Science 144, 1019 (1964). 



Reen, R. van: The Influence of parathyroid extract on bone metabolism and the levels of 

 Nicotinamide nucleotides. The parathyroid glands, ultra structure, secretion and function. 

 Chicago: The University of Chicago Press 1965. 



Vaes, G.: Hydrolytic enzymes and Lysosomes In bone cell. In Calcified Tissues. Richelle, 

 L. J., and M. J. Dallemagne (eds.). Liege: Universlte de Liege 1965, p. 51. 



Voogd van der Straaten, W. a. de: The possible role of NADP In the action of para- 

 thyroid hormone on bone. The parathyroid glands, ultra structure, secretion and function. 

 Chicago: The University of Chicago Press 1965. 



