KOSPHORYLASE 



GLUCOSE METABOLISM 

 giuco3« 



KJNASE 



HEXOKJ 



G6 PDH 



NADP* ^^NADPH, *-^^'' 



.b 6 - phosphogluconott 



6PG0H 



NAD PH. * 



froctosp-6- phosphofc 

 ffucfose -1,6 -diphosphote 



NADPH 

 flbulose-5- phosphate 



{Jihydfo< yocetone * 

 phosphofe 



t ALOOLAS 



Pentose Shuni 



glyceroldehyde - 3 - 

 phosphate 



Fig. 1. 



The glycolytic pathway. Under anaerobic conditions pyruvate is converted to lactate with 

 the concomitant oxidation of NADH 2 toNAD. (FromMarkert, in The Harvey Lectures, Series 

 59, 187, 1965; reproduced with permission of Academic Press.) 



isozymes. In 1959 a very sensitive and con- 

 venient method for analyzing LDH in tissue 

 homogenates was developed by Markert and 

 Miller (1). They coupled starch gel electro- 

 phoresis with a histochemical staining pro- 

 cedure for visualizing dehydrogenases. This 

 facilitated the clear demonstration of tissue, 

 ontogenetic, and species specificity of LDH 

 isozyme patterns as well as the isozymes of a 

 variety of other enzymes. With these data the 

 biological significance of isozymes received 

 general recognition As more data were accumu- 

 lated it became apparent that most mammalian 

 tissues contain five principle LDH isozymes and 

 that the electrophoretic mobility of isozymes 

 exhibits a high degree of specificity, as illus- 

 trated in Fig. 2. 



Although there are readily discernible dif- 



ferences in electrophoretic mobility among the 

 homologous LDH isozymes of widely different 

 vertebrate species, it is observed that the over- 

 all isozyme patterns of homologous tissues are 

 remarkably similar. This is clearly illustrated 

 by comparing the LDH isozyme patterns of a 

 given tissue, such as heart muscle, from several 

 species as in Fig. 3. In general, vertebrate 

 heart muscle is richest in the more rapidly 

 migrating isozymes, LDH-1 and LDH- 2, while 

 vertebrate skeletal muscle is richest in LDH- 5 

 and LDH-4. At the present time, the major 

 apparent exceptions to this generalization are 

 found among the fishes. For example, as shown 

 in Fig. 4, the heart muscle of the whiting ex- 

 hibits a remarkably bizarre pattern of LDH iso- 

 zymes which is difficult to interpret. A few 

 other exceptions should be noted. Skeletal muscle 



78 



