BioMed Realty Trust continues to push the life sciences conversion wave in Boston, quietly taking over two prominent development sites.

The Blackstone-backed life sciences investor has entered a purchase agreement with a joint venture for the existing 1000 Washington St. office building and rising 321 Harrison St. development, it announced Monday in a public filing. The adjacent buildings in the South End are BioMed’s latest play to capture the lab market's sky-high demand amid meager supply.

Developers Nordblom and CIM jointly owned the 11-story, 242K SF office building at 1000 Washington St. and previously planned a 235K SF, eight-story office building atop the parking garage at 321 Harrison St. BioMed will make minimal changes to the already-constructed core and shell at 321 Harrison St., but plans to add more robust mechanical systems, it said in its filing with the Boston Planning and Development Agency.

The Blackstone subsidiary didn’t elaborate on its plans for 1000 Washington St. The companies didn't respond to requests for comment Tuesday, and the transaction details weren't available in Suffolk County land records.

The 321 Harrison St. site has no committed tenants, and BioMed wrote anticipated lab, research and development uses at the site will generate types and quantities of waste “common to most laboratory research facilities.” Modifications to the building could begin as early as June, BioMed said in the filing.

The new disclosure has heightened relevance as city councilors and community representatives demand more oversight of the city’s surge of lab projects. Residents have professed uncertainty over the type of research coming into their neighborhoods. The 1000 Washington St. building houses state government offices and retail tenants.

BioMed’s new acquisitions sit miles from 601 Congress St., the 14-story former John Hancock Life Insurance Co. headquarters it bought from Manulife for $362M in December.