E*Trade

(ET) - Get Report

is wasting no time cashing in on the proposed merger of the

New York Stock Exchange

and

Archipelago Exchange

(AX) - Get Report

.

The online brokerage filed with the

Securities and Exchange Commission

to sell 529,731 shares of Archipelago stock -- just about its entire stake in the electronic stock exchange.

E*Trade filed its notice to sell on April 21, a day after the surprise merger was announced. That day, Archipelago shares surged 60% to close at just under $30 a share.

From the filing, it's not clear whether E*Trade has actually sold its shares yet. But assuming the financial firm sold them for about $30 a share, the transaction would have generated $15.9 million in gross proceeds.

An E*Trade spokeswoman could not be reached for comment.

E*Trade was one of the original investors in Archipelago, which began as an electronic communications network. Last August, Chicago-based Archipelago went public in a $126 million initial public offering. In the IPO, E*Trade sold 232,803 shares.

After the Archipelago IPO, E*Trade held a 1% equity stake in the electronic stock market.

To date, E*Trade is the first big original investor in Archipelago to sell shares in the aftermath of the deal with the NYSE.

Big Board executives currently are traveling the country, trying to sell the deal to the NYSE's members. The sales job is an attempt to squelch opposition to the merger, which is being fueled by

Home Depot

(HD) - Get Report

founder Kenneth Langone.

Langone, a controversial former NYSE director, claims the Big Board's 1,300 member seat holders are getting short-changed in the transaction. But many on Wall Street are wary of Langone, because he is close friends with former Big Board Chairman Richard Grasso and helped win approval for Grasso's outsized $140 million pay package.

Most don't expect Langone to succeed in putting together a group to buy the NYSE and scuttle the Archipelago deal, despite abundant media coverage.

Meanwhile, the Archipelago/NYSE merger is proving to be quite a windfall for

Goldman Sachs

(GS) - Get Report

, which is one of the biggest equity investors in the electronic exchange. Goldman and its subsidiaries own 7.3 million shares, or 15% of the electronic exchange's outstanding stock. The value of Goldman's investment has risen by $84 million since the deal was announced.

In recent days, the storied investment bank has come under fire for serving as merger adviser to both Archipelago and the NYSE. Archipelago disclosed recently that it paid a $3.5 million advisory fee to Goldman. Additionally, Goldman owns 21 member seats at the NYSE, whose value has risen by $20 million in value because of the deal.

Langone has indicated that one of the reasons he launched his rival, some might say quixotic, bid for the NYSE is Goldman's dual role as kingmaker and investor in the deal.