Arrowhead Research Corp. said Monday that it had agreed to increase its ownership in its majority-owned Unidym Inc. subsidiary through a stock exchange with other Unidym shareholders.

The Pasadena company, which invests in nanotechnology companies focused in the life sciences, electronics and energy, said it is exchanging 1.5 million of its common shares for the same number of Unidym “Series A” preferred stock. The transaction will increase its ownership from 51.5 percent to 58.1 percent.

Unidym is a Menlo Park company that makes high-value carbon nanotubes for industrial uses such as electronic displays. The agreement provides for a one-year lock up on sales of the exchanged Arrowhead stock.

Arrowhead shares closed down 1 cent, or 1.5 percent, to 61 cents on the Nasdaq.