58 



BIOCHEMICAL SYSTEMATICS 



were quite constant and similar among related species. Dessauer 

 speculated that variation in the transferrin pattern might be greater 

 in species in a more active phase of evolution. The results in general, 

 while they raised a number of questions, indicated that the iron- 

 binding proteins might be of considerable value in direct systematic 

 comparisons or in population studies when intraspecific variation is 

 encountered. 



Another method of studying comparative enzymology which 

 appears to be very promising has been described recently by Kaplan 

 et al. (1960), and Kaplan and Ciotti (1961). This technique involves a 

 comparison of the catalytic properties of selected enzymes. Several 

 related methods have been utilized by Kaplan's group. For example, 

 they have shown that certain diphospho-pyridine nucleotidases of 

 ruminants (for example, goat, beef, lamb, deer) are inhibited strongly 

 by isonicotinic acid hydrazide while those of a number of other 

 mammalian groups, as well as the frog, are relatively insensitive. This 

 implies a distinctiveness in these enzymes in one related group of 

 mammals which is systematically significant. 



In the work reported by Kaplan et al. (1960) reaction rates 

 were compared at high and low substrate concentration using the 

 "same" enzyme from a relatively wide assortment of vertebrates. The 

 specific enzyme reported on was lactic acid dehydrogenase, using both 

 lactate and pyruvate as substrates. In addition to the normal diphos- 

 phopyridine nucleotide (DPN) cof actor they prepared specific analogs 

 of the pyridine ring of DPN such as acetyl pyridine and thionicotina- 

 mide. These cofactors participated in the reaction either as electron 

 donors (with pyruvate) or acceptors (with lactate). Table 4-1 presents 

 some of Kaplan's results. The values reported could be duplicated, 

 according to the authors, within a few per cent when a number of dif- 

 ferent individuals of the same species were analyzed. 



One notable feature of the data from Table 4-1 is the fact 

 that ratios for heart muscle and for skeletal muscle of the same 

 species consistently differed. Also there were outstanding differences 

 in the ratios of flounder, sole, and halibut (all flatfishes) as opposed to 

 the other animals, including a number of other fishes. Differences, 

 though somewhat less marked, were typical between the enzymes of 

 most of the species examined, giving the impression that, if these re- 

 action rate differences truly reflected enzyme structural differences, 

 all of the animals possessed different enzymes. The authors were 

 conservative, however, and did not stress the smaller differences in 

 ratio. A few additional analyses were carried out with invertebrates, 

 and extremely wide differences were observed, notably a greatly en- 

 hanced affinity of the enzyme with the pyridine analog, acetyl 

 pyridine, in crustaceans. 



