Compared to the rest of the East Loop submarket, that defies gravity. The overall vacancy rate in the 21.3-million-sf submarket totals 16%, according to Cushman & Wakefield's first quarter report, surpassed only by the 20.8% of space available in Downtown's smallest submarket, River North.

Although financial details were not disclosed, Parkway Properties vice president and asset manager Will Flatt says the deal involves no tenant improvements. "There was some rent concession involved," Flatt tells GlobeSt.com. "But at the end of the day, we were pleased, and I think they were pleased."

Flatt was helped by Brian Whiting of JF McKinney & Associates, Parkway's exclusive leasing representative at 233 N. Michigan Ave. Alain of Newmark Realty handled negotiations for World Book.

"It really restabilizes our building," says Flatt, adding occupancy is being buoyed by smaller deals. Occupancy was 89% when Parkway Properties took the keys from former owner Tishman-Speyer. However, 13% of the building was leased by bankrupt internet consulting firm March First.

Flatt remains patiently bullish on the East Loop submarket, having been involved in talks involving two nearby buildings in recent years. After taking a pass on 111 E. Wacker Dr., Parkway Properties most recently was exploring 303 E. Wacker Dr. before talks with current owner Hines Interests ceased. "Fundamentals were falling, and prices were rising," Flatt says.

The Jackson, MS-based REIT paid $173.5 million for 233 N. Michigan Ave., also known as Two Illinois Center, in 2001. The following year, it sold a 70% interest in the building to New York City-based Investcorp for $125 million.