At first sight, this limitation might contribute to setting the whole organism pejus temperature, where capacity limitations set in. Yet, due to their lower level of organisational complexity, thermal tolerance windows of organelles generally span a wider temperature range than those of the whole organism. Notably however, Bilyk & De Vries and Beers & Sidell found acute critical thermal maxima for N. coriiceps and N. rossii around 16�C17uC. Nonetheless, mitochondrial efficiency appears to be safeguarded in the two nototheniids: RCRs were stable over the experimental temperature range, indicating rather static mitochondrial leak rates independent of temperature. Hardewig and colleagues as well as Johnston and colleagues report RCR + values between 7 and 10 for Antarctic notothenioids, which correspond to apparent proton leak rates of 10�C15%. The mean leak rates observed for liver mitochondria of the two nototheniids in this study were only slightly higher than these values. As a possible consequence of stable RCR +, ADP/O ratios also remained unchanged over the thermal range in this study in both nototheniids. They were higher than the values reported by Hardewig and colleagues for L. nudifrons, but similar to those observed in short-horn sculpin M. scorpio and rainbow trout. In the range of 0�C15uC, both complexes display ADP/O ratios similar to or even higher than active temperate fish species, especially so in N. coriiceps. In terms of ADP generation, complex I can be thus assumed to be as efficient and thermally stable as complex II in the two nototheniids. The protein instability indices underline the general notion that decreased thermal BI-D1870 S6 Kinase? inhibitor stabilities of cold-adapted enzymes are the side effects of an increased flexibility, which is considered a precondition for proper function at low temperatures and may also have been a pre-adaptation for the Antarctic notothenioid lineages to radiate into the Southern Ocean. Modifications to increase Nilotinib abmole bioscience flexibility may include a decrease in weak interactions and hydrophobicity, as well as substitution and deletion of specific amino acids. In this respect, nototheniid ND6 may not only have undergone a translocation, but also some changes in composition. Table 3 lists the percentages of the individual amino acids in ND6. In fact, there are not only composition differences between the Notothenioid/eelpout and temperate/Arctic/tropical group but also between the two nototheniid species and the related sub-Antarctic notothenioid E. maclovinus. E. maclovinus has been described as ��notably divergent from the rest of the notothenioids�� in terms of protein composition, which appears to carry characteristics of both groups in its ND6 composition: the 3 Antarctic species and the sub-Antarctic notothenioid bear lower leucine contents than the non-Antarctic groups, but higher percentages of cysteine, which is even more prominent in the nototheniids.