Astrazeneca Pharmaceuticals sold its 43-acre campus in Waltham for $273 million as it prepares to depart for a Kendall Square development.

Alexandria Real Estate Equities acquired the 35 Gatehouse Drive property, according to a Middlesex Registry of Deeds filing.

In April, Astrazeneca leased 570,000 square feet at 290 Binney St. in Cambridge. Boston Properties is redeveloping the 1.7-acre Kendall Square site, currently occupied by the 6-story Blue Garage, with a pair of lab buildings, a residential tower and a new Eversource substation. Astrazeneca is scheduled to occupy the Cambridge facility in 2026, consolidating its local real estate which also includes leased space at 121 Seaport Blvd. in Boston by its subsidiary, Alexion Pharmaceuticals.

The Waltham property is Astrazeneca’s Gatehouse Park BioHub, which opened in 2015. It includes a 274,871-square-foot R&D and flex building, according to Waltham assessors’ data.

The Dec. 29 transaction included a $70 million mortgage from Alexandria Finance LLC.

Pasadena, California-based Alexandria, the biggest U.S. life science landlord, owned 431 properties totaling 41.1 million square feet as of Sept. 30.

In Greater Boston, Alexandria has an 11 million-square-foot portfolio, and another 2.9 million square feet of development activity. Its current projects include a partnership with Samuels & Assoc. on two new life science buildings at 201 Brookline Ave. and 401 Park Drive in the Fenway.