PROGRESS IN PROTOZOOLOGY

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pattern; they do confirm our judgement that all the species studied
are very far from a common ancestor.
As we have seen, some nucleic molecules are very stable, while
others are relatively labile. The same observation can be made for
proteins. An example of a very unstable protein, at least unstable for
the attribute examined, is the immobilization antigen. Tetrahymenas are
readily immobilized by antisera prepared against them (Margolin
et al. 1959), and the sensitive immobilization test has facilitated considerable
work on the genetics and regulation of molecules involved
(Doerder 1979). Thus far, antisera prepared against one species of
the T. pyriformis complex have never been found to immobilize strains
of another species, even at much higher concentrations (N a n n e y,
unpublished, Grass, unpublished). Moreover, antisera prepared against
whole cells usually form no sharp bands in heterologous agar diffusion
tests. The antigenic properties of the immobilization antigens, and of
most other major antigenic molecules, are too unstable to provide estimates
of evolutionary distances within the complex.
Very much the same sense of large but unmeasurable molecular distances
comes from the electrophoretic analysis of certain enzymes. The
esterase enzymes, like the mitochondrial DNAs, are (notoriously variable
in most organisms and useful chiefly in discriminating among closely
related species. Allen and Weremiuk (1971) carried out a survey
of the esterases in a number of species of the T. pyriformis complex,
attempting to describe not only their electrophoretic properties but
their specificities. Starting with T. thermophila, they defined three classes
of esterases (Table 10) on the basis of their substrates and inhibitors.
Table 10
Classes of esterases demonstrable in Tetrahymena species . Enzymes noted in parentheses
not observed in all strains examined
Species Esterase-1 Esterase-2 Esterase-3 Summary
T. thermophila (1) + + + + + +
T. americanis (2) + + + + +
T. borealis (3) + - + + - +
T. hegewischi (5) - - + 4-
T. canadensis (7) + + + + + +
^ • < 6 — — —
>
T. pigmentosa ^ — — —
T. tropicalis (9) + + + + + +
T. hyperangularis (10) - - —
T. australis (11) - + + - +
T. capricornis (12) - -f + - + +
Allen and Weremiuk (1971).
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