A surge in the prices of shares in Japan’s trading houses — triggered by a $6 billion investment by Warren Buffett — is already fading, due to a lack of fresh catalysts and a downturn in commodity markets.

Shares in two of the five sōgō shōsha, as the commodity-centric Japanese conglomerates are called, are now trading at or below levels before Buffett’s Berkshire Hathaway Inc. announced its stake purchase.

The August announcement, among the largest investments ever made by Buffett in Japan, not only sparked a rally in stocks, but also boosted overall investor interest in the trading companies.