Photo courtesy of Bruce T. Martin Photography

Life science developer Alexandria Real Estate Equities has bought its second suburban Boston office property in the past month, acquiring a Newton complex near the MBTA’s Riverside station for $235 million.

Alexandria acquired the 509,702-square-foot Riverside Center at 275 Grove St. from Houston-based Hines, after buying Athenahealth’s 760,000-square-foot Watertown campus in late December for $525 million.

The Riverside complex has flexible floor plates and a newly renovated cafe and fitness center, according to JLL Boston, whose capital markets team represented the seller. The complex also sits near the Route 128-Massachusetts Turnpike interchange.

The two transactions nearly double Alexandria’s portfolio in the Route 128 submarket. As of Sept. 30, Alexandria owned 5.4 million square feet of commercial real estate in Greater Boston, comprising 24 percent of its North American portfolio. Approximately 1.1 million square feet were located in the Route 128 submarket.