Merrill Lynch Securities Co. on Saturday became the first of six U.S. and British firms scheduled to begin trading on the Tokyo Stock Exchange, ending a 36-year-old monopoly by Japanese companies over the world's second-largest stock exchange . . . Litton Microwave Cooking Products, a division of Litton Industries, will move its operations from Plymouth, Minn., to Memphis, Tenn., transferring about 70 employees and laying off 355 . . . Boeing Co. announced the completion of its previously reported purchase of De Havilland Aircraft of Canada from the Canadian government . . . Varian Associates said it is reducing the work force of its microwave tube division in Palo Alto by 6%, or about 100 employees . . . Dart & Kraft reported the completion of the sale of its Kitchenaid operations to Whirlpool for $150 million in cash, subject to post-closing audit adjustments.