A scientist is studying a protein that is present on the plasma membrane of cells. He therefore purifies the protein in a lipid bilayer and subjects it to a number of conditions. His investigations show that the protein has the following properties: 1) It is able to change ion concentrations across the membrane without addition of ATP to the solution. 2) Its activity increases linearly with substrate concentration without any saturation even at mildly supraphysiologic conditions. 3) In some states the protein leads to an ion concentration change; whereas, it has no effect in other states. 4) Changing the electrical charge across the membrane does not affect whether the protein has activity. 5) Adding a small amount of an additional substance to the solution reliably increases the protein's activity. These findings are consistent with a protein with which of the following functions?
AMaintenance of resting sodium and potassium concentrations
BTransporting water in the collecting duct of the kidney
CReabsorption of glucose in the proximal kidney tubule
DMediating neuronal to muscle end plate communication
ECausing depolarization during action potentials
A 22-year-old woman presents to the emergency department with a 2-day history of severe blistering. She says that she woke up 2 days ago with a number of painful blisters in her mouth and has since been continuing to develop blisters of her cutaneous skin all over her body and the mucosa of her mouth. She has no past medical history and has never experienced these symptoms before. Physical exam reveals a diffuse vesicular rash with painful, flaccid blisters that separate easily with gentle rubbing. The function of which of the following proteins is most likely disrupted in this patient?
AT-cell receptor
BCadherin
CKeratin
DCollagen
EIntegrin
A researcher is studying proteins that contribute to intestinal epithelial permeability. He has isolated intestinal tissue from several mice. After processing the tissue into its individual components, he uses a Western blot analysis to identify a protein that forms part of a multi-protein complex at the apical aspect of epithelial cells. The complex is known to provide a diffusion barrier between the apical and basolateral aspects of epithelial cells. Which of the following proteins is this researcher most likely investigating?
AIntegrin
BConnexon
CDesmoglein
DE-cadherin
EClaudin
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