Suppose you are working for Big Pharma on a project to develop new inhibitors of lysosome acidification. Your assay system involves incubating isolated lysosomes in buffers containing various drugs for defined periods of time, followed by measurement of intraluminal pH. You discover a new compound that is extremely potent at preventing acidification, and prematurely assume that it is a proton pump inhibitor. During subsequent verification experiments, however, this compound does not bind to ANY components of the proton pump complex. Can you think of another, unrelated membrane protein that this drug may be targeting