Five leases totaling 51,056 square feet have been signed at 281 and 321 Summer St. in South Boston.

Space with a Soul, a nonprofit mission accelerator, has leased 14,592 square feet at the seven-story, 173,241-square-foot office building at 281 Summer St., according to a statement. Space with a Soul was represented by Deb Stevens, principal of Boston-based The Stevens Group, in the lease transaction.

The remaining four leases were executed at the eight-story, 93,964-square-foot building at 321 Summer St.

AisleBuyer LLC, a mobile self-checkout software company, has leased 10,813 square feet on the eighth floor of 321 Summer St. Landmark Real Estate Advisors’ Principal Eric Solem and Partner Robert Elmer represented AisleBuyer in the lease transaction.

Zmags, an online publishing platform provider, has leased 10,635 square feet on the third floor of 321 Summer St. Zmags was represented by Graham Allison, assistant broker, and Mark Cote, managing director/co-founder, of T3 Advisors.

Apperian, a mobile application management firm, has leased 8,903 square feet on the first floor of 321 Summer St. Apperian was represented by Matt Godoff, advisor, and Karyn McFarland, senior vice president, of Grubb & Ellis.

Architecture firm isgenuity LLC has leased 6,113 square feet on the fourth floor of 321 Summer St. Boston Realty Advisors’ Adam Schneier, managing director, represented isgenuity in the lease transaction.

The CB Richard Ellis/New England team of Bill Crean, senior vice president/partner; Ogden White, senior vice president/partner; and Tim Howe, vice president, represented the landlord of both buildings, Normandy Real Estate Partners, in all of the lease transactions.