TOKYO, Oct 4 A major shareholder in Tokyo-based property investor Simplex Investment Advi

TOKYO, Oct 4 (Reuters) A major shareholder in Tokyo-based property investor Simplex Investment Advisors Inc , Yoshihiro Mikami, has put his 29 percent stake up for sale, sources familiar with the deal said.

Goldman Sachs and fund management firm Aetos Capital were said to be interested in the stake, they said.

The chief executive of Aetos Japan, Scott Kelley and a spokeswoman for Goldman declined to comment.

Attempts to reach Mikami, who is travelling outside Japan, were unsuccessful. A Simplex Investment spokesman said was not in a position to comment on the actions of a shareholder.

A deal may still falter, the sources said, because of disagreements over valuation of the stake in Simplex, which has a market value of $808 million. Mikami's stake is worth about $240 million at the current market price.

As of March 2007 the firm had 622 billion yen ($5.3 billion) under management.

Simplex shares jumped 12 pct on Thursday to 130,000 yen, taking gains to about 85 percent from an all-time low of 70,300 yen hit mid-September, and markedly outperforming a 29 percent gain for Tokyo's real estate sub-index <.irlty.t> in the same period.

Japan's $40 billion property trust market has ended a five-year bull run with a steep fall in recent months, prompted by a global liquidity squeeze and warnings of a 1980s-style price bubble and crash.

The falls have stoked speculation of a takeover frenzy by the stronger property firms and by private equity funds, which has helped prices claw back some ground.

Billions of dollars have been raised globally in the last year for booming Asian property markets, with the likes of Morgan Stanley , Blackstone Group and Goldman Sachs active in Japan.

Simplex Investment Advisors has three main business segments, asset management of real estate funds in Japan, the development and marketing of property.

Mikami acquired 211,640 shares in Simplex on December 15 last year, becoming the firm's second largest shareholder, behind Nikko Cordial which holds 42.5 percent.

Nikko Cordial declined to comment.

The winning bidder may also want to launch a tender offer for the rest of the company, but it was unclear whether this would have the consent of Simplex's management or other key shareholders.

UBS is helping Mikami organise the auction, the sources said. A UBS spokeswoman in Tokyo declined to comment.

($1=116.59 Yen) (Additional reporting by Taro Fuse, Emi Emoto and Nathan Layne in Tokyo and Dominic Whiting in Manila) REUTERS KR VC2019