72 The Nature of Biological Diversity 



ogy between oxidative phosphorylation and muscle contraction, 

 will be presented. 



Some relations of amino aeid composition 

 to activity 



Amino acid composition and partial or complete amino acid se- 

 quence studies have shown only small differences in proteins with a 

 particular biological activity from different animal species, namely, 

 with insulins, hemoglobins, and some pancreatic enzymes. Small but 

 detectable differences in enzymes from one tissue have also been 

 found and the recognition of such variants will likely increase as more 

 discerning methods are applied. Markert has appropriately termed 

 such closely related enzymes "isozymes" (11. The similarities of the 

 protein structure of the same enzyme from different tissues is illus- 

 trated by the immunological cross reactions among various mammalian 

 tissue lactate dehydrogenases (2), as well as various lactate dehydro- 

 genases from a single tissue (1) . Differences in composition are also 

 shown by differences in catalytic behavior of purified lactate dehydro- 

 genases from different tissues, as documented by Kaplan and co- 

 workers (3). Such differences may have clinical use in identification 

 of the source of an enzyme from its properties. 



One aspect of amino acid composition of enzymes of particular 

 recent interest has been the demonstration of the presence of a similar 

 amino acid sequence near the reactive seryl residue of a variety of 

 hydrolytic enzymes. Pertinent findings are summarized in Table 1. 



Table 1. Amino acid sequences near reactive seryl 

 residues of some hydrolytic enzymes 



Enzyme Sequence 



Trypsin -Glycyl-aspartyl-seryl-glycyl- 



Chymotrypsin -Glycyl-aspartyl-seryl-glycyl- 



Thrombin -Glycyl-aspartyl-seryl-glycyl- 



Elastase -Glycyl-aspartyl-seryl-glycyl- 



Liver aliesterase -Glycyl-glutamyl-seryl-glycyl- 



Pseudocholinesterase -Glycyl-glutamyl-seryl-glycyl- 



Bacterial proteinase -Threonyl-seryl-methionyl-alanyl- 



sources: Original data for the first six enzymes are cited 

 in (4) ; the sequence for bacterial proteinase is given by 

 Sanger and Shaw (5). 



