. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HEMOCYANIN SUBUN1TS IN ARTHROPODS 109 half - saturation oxygen pressu re (Pso). cooperativity ( n50) FIGURE 7. Illustration of the functional plasticity of native 4 X 6-meric hemocyanin of the tarantula Eurypelma califomicum, compared to the functional inflexibility, and the very different behavior, of the isolated subunits. Subunits (small black areas) show a low p50 around 5 mm Hg, a high oxygen affinity. This behavior is independent of pH (= no Bohr effect). Moreover, they are non-cooperative (hyperbolic oxygen bindin
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HEMOCYANIN SUBUN1TS IN ARTHROPODS 109 half - saturation oxygen pressu re (Pso). cooperativity ( n50) FIGURE 7. Illustration of the functional plasticity of native 4 X 6-meric hemocyanin of the tarantula Eurypelma califomicum, compared to the functional inflexibility, and the very different behavior, of the isolated subunits. Subunits (small black areas) show a low p50 around 5 mm Hg, a high oxygen affinity. This behavior is independent of pH (= no Bohr effect). Moreover, they are non-cooperative (hyperbolic oxygen binding curve: n50 = 1). All subunits behave similarly (Decker et al. 1979; Mark! et ai, 1981e). In contrast, the 4 x 6-mer (large white rectangles) shows p50 values up to 30 mm Hg (at pH ), or low oxygen affinities. Moreover, it exhibits impressive cooperativities (sigmoid oxygen binding curves); the maximum at pH goes up to n50 = 8 and more. Oxygen affinity, and also cooperativity, are both strongly pH dependent (Loewe, 1978), which is highly adaptive with respect to the animal's physiology and behavior (Angersbach, 1978). We recently detected that, although the natural resting blood pH of the tarantula is (Angersbach, 1978), the in vivo behavior of the 4 X 6-mer should be like that illustrated here for pH ; calcium and magnesium ions in native concentrations (4 mAl each) modulate the function correspondingly (B. Markl and J. Markl, unpub.). All in all, this aggregate of 24 functionally limited components displays completely novel physiological properties. These systemic characters are created by subunit interaction phenomena, and cannot be predicted from the behavior of the isolated subunits. To study the molecular organization of those interactions, one attempt is to analyze the abilities of oligomeric dissociation fragments (Savel et al., 1983, 1986); for example in the 1 x 6 quarter-structure (areas on the left of the dashed lines), the 4 X 6-mer's oxygen affinity
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
