Tissue distribution and development of some cartilage enzymes

Abstract

The two “cartilage enzymes,” UDPG-4-epimerase and UDPG-dehydrogenase, are present in the 15-day chick embryo sternum at levels about 25 times higher than those found in noncartilage tissues. The “ubiquitous” enzyme, phosphoglucose isomerase, on the other hand, shows a remarkably uniform distribution in all tissues. The normal development of the cartilage enzymes relative to the ubiquitous enzyme was studied beginning with the 2-day embryo. The epimerase is found in all early tissues at the same low level as in the 15-day noncartilage tissues. About the fourth incubation day it begins to rise in whole somites, but not in nonchondrogenic tissues. By using mild sonication to break off the softer perichondrial mesenchyme, it was possible to obtain and assay pure chondrified sternal tissue beginning with the 9-day sternal plates. Both cartilage enzymes, but not the isomerase, increase steeply during the histological maturation of sternal cartilage between days 9 and 16. This maturation phase of the development of the cartilage enzymes is probably due to the cessation of cell division, since interstitial growth in the sternum is gradually halted during this period.