»#• »t2 »t3 M «nl «n2 Wn3 



EMBRYO 



ADULT NUCLEUS 





tfti »t2 b«3 bt4 ttel bc2 be^ be^ 

 EMBRYO ADULT CORTEX 



Fig. 8. 



Electrophoretic analysis of y -crystallins from adult and embryonic bovine lenses. The 

 conditions of electrophoresis are the same as described in Fig. 7. (Fig. 6, J. Papacon- 

 stantinou, Biochim. Biophys. Acta 107, 81, 1965; reproduced with permission of Elsevier 

 Publishing Company.) 



their availability for recombination with LDH- 1 

 subunits. 



We interpret these data to indicate that 

 during the aging of lens epithelial cells (calf 

 to adult) there is a regulation of LDH subunit 

 synthesis such that there is a greater decrease 

 in the synthesis of LDH-5 subunits than LDH-1 

 subunits. Furthermore, this tendency for the 

 persistence of LDH-1 becomes more pronounced 

 during the differentiation of the epithelial cell 

 to the fiber cell in both the calf and adult lens. 

 The extreme case is seen in the adult cortex 

 fiber cells where LDH-1 is essentially the only 

 one of the 5 isozymes remaining. Finally, we 

 would like to correlate this with the replicative 

 ability of the cell. When these cells, which 

 retain their ability to replicate, reach a phase 

 analogous to the stationary phase of a logarith- 

 mic growth cycle the synthesis of LDH-1 



subunits is favored. This is also the case when 

 the cells reach a stage of differentiation in 

 which they have lost their replicative capacity 

 (the fiber cells). 



C. LDH isozymes and lens 

 carbohydrate metabolism 



I would like to digress from the main theme 

 of my talk for one moment to correlate the LDH 

 isozyme data just presented with the metabolic 

 activity of the lens epithelial cells and fiber 

 cells. A possible role of the regulation of 

 carbohydrate metabolism in skeletal and heart 

 muscle has been attributed to the persistence of 

 different LDH isozymes in these tissues. It has 

 been observed that LDH-1 is the predominant 

 isozyme in tissues exhibiting high rates of 

 oxidative metabolism, such as embryonic and 



55 



