Hypothesis for a serine proteinase-like domain at the COOH terminus of Slowpoke calcium-activated potassium channels

Bovine pancreatic trypsin inhibitor (BPTI) is a 58-residue protein with three disulfide bonds that belongs to the Kunitz family of serine proteinase inhibitors. BPTI is an extremely potent inhibitor of trypsin, but it also specifically binds to various active and inactive serine proteinase homologs with KD values that range over eight orders of magnitude. We previously described an interaction of BPTI at an intracellular site that results in the production of discrete subconductance events in large conductance Ca2+ activated K+ channels (Moss, G.W.J., and E. Moczydlowski. 1996, J. Gen. Physiol, 107:47-68). In this paper, we summarize a variety of accumulated evidence which suggests that BPTI binds to a site on the KCa channel protein that structurally resembles a serine proteinase. One line of evidence includes the finding that the complex of BPTI and trypsin, in which the inhibitory loop of BPTI is masked by interaction with trypsin, is completely ineffective in the production of substate events in the KCa channel. To further investigate this notion, we performed a sequence analysis of the alpha-subunit of cloned slowpoke KCa channels from Drosophila and mammals. This analysis suggests that a region of approximately 250 residues near the COOH terminus of the KCa channel is homologous to members of the serine proteinase family, but is catalytically inactive because of various substitutions of key catalytic residues. The sequence analysis also predicts the location of a Ca(2+)-binding loop that is found in many serine proteinase enzymes. We hypothesize that this COOH-terminal domain of the slowpoke KCa channel adopts the characteristic double-barrel fold of serine proteinases, is involved in Ca(2+)-activation of the channel, and may also bind other intracellular components that regulate KCa channel activity.     

Assimilation efficiency of adult Kittiwakes and Brünnich's Guillemots fed Capelin and Arctic Cod

The mean assimilation efficiencies of 10 adult Kittiwakes (Rissa tridactyla) and 10 Brünnich's Guillemots (Uria lomvia) fed on Capelin (Mallotus villosus) were 77.5% and 74.4%, respectively. When fed on Arctic Cod (Boreogadus saida) they were 83.1% and 78.2%, respectively. After correction for nitrogen retention, the assimilation efficiencies decreased to 72.2%, 70.6%, 81.2% and 74.7%, respectively. Kittiwakes and Brünnich's Guillemots seem to have the same ability to utilize the energy of the different food items. The differences in assimilation efficiencies when fed two fish species was mainly related to the fat content of the fish.     

Oxidative capacity of tissues contributing to thermogenesis in eider (Somateria mollissima) ducklings: changes associated with hatching

1. The development of liver and skeletal muscle oxidative capacities during hatching of the common eider (Somateria mollissima) in the Arctic has been investigated by monitoring tissue cytochrome c oxidase activity. 2. The specific activity of the liver enzyme did not change as the embryo underwent hatching, nor during subsequent growth of the duckling into adulthood. 3. Thigh muscle enzyme specific activity increased by a factor of 3.4 during the 24 h prehatching period, remained elevated for at least 48 h after hatching, and then returned to the embryonic (-24 h) level in adults. 4. Histochemically visualized NADH-tetrazolium reductase of a typical red thigh muscle, M. vastus lateralis, showed a distinct increase in activity as the hatching process progressed to completion. 5. Electron microscopy of sectioned M. vastus lateralis revealed a dramatic increase in the density of the myofibrillar structure (number of mitochondrial profiles per unit area), and in the surface area of mitochondrial crista membranes in the course of the 48 h interval from 1 day prehatching to 1 day after hatching. 6. The significance of these changes for the scaling of thermoregulatory heat generation in the newly hatched eider duckling is discussed.