LACTATE DEHYDROGENASE ISOZYMES OF PENGUIN PYGOSCELIS-ADELIAE

The complex isozyme patterns of lactate dehydrogenase (LDH) in penguin (Pygoscelis adeliae) tissues were examined at several successive stages in embryonic development by starch‐gel electrophoresis. The relative quantities of the isozymes were measured by densitometry, and the subunit composition of each isozyme was analyzed by molecular hybridization. The complexity of the isozyme pattern varied greatly with the conditions of electrophoresis but maximum resolution was obtained with a neutral Tris‐citric acid buffer of low ionic strength. When electrophoresis was carried out with this buffer at 4°C, as many as fifteen isozymes were resolved. Only five isozymes can be distinguished at high ionic strength. The fifteen isozymes can be classified into five groups, each group corresponding to one of the five major LDH isozymes found in mammals and birds. The validity of this classification was tested by molecular hybridization with beef and horse LDH, the subunit composition of which is known. The pattern of hybrid molecules produced suggests that penguin LDH contains three different subunits that may generate fifteen isozymes by random association as tetramers. To test the binomial proportions among the isozymes a quantitative photometric assay was developed for measuring enzyme activity in terms of formazan deposited on a starch gel during the staining reaction for LDH. Only at low enzyme concentrations is the deposited dye linearly proportional to the amount of enzyme. The relative abundance of the isozymes in most tissues approximated a binomial distribution. Tissue spcific patterns revealed that anodal isozymes predominate in heart, ovary and liver and cathodal isozymes in lung and muscle. However, in contrast to mammalian tissues, the penguin patterns are not sharply skewed. All isozymes are reasonably abundant in all adult tissues. In early embryonic stages of development all tissues contained greater proportions of LDH‐1, but a shift in isozyme distribution gradually took place during the course of development to enrich enzyme activity at the LDH‐5 end of the spectrum in late embryonic and adult tissues. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company