Semperian LLC, which services loans for General Motors Acceptance Corp., said Monday it is laying off 45 employees, or about 13 percent of its Knoxville work force, effective Dec. 31. This will leave about 300 employees at the company's call center at 2420 Cherhala Blvd. in the Pellissippi Corporate center, said Mike Stoller, spokesman for GMAC, parent company for Semperian. "This is part of an ongoing…