A patent for no-calorie sugar that could potentially replace artificial sweetners suspected of causing cancer has set off a buying binge for the stock of Biospherics Inc. of Rockville.

In heavy over-the-counter trading, Biospherics stock has jumped from $3 a share to $9 this week in trading volumes that ran as high as 10,000 shares a day.

The stock price has soared on speculation about the potential profits of a patent granted last week to Biospherics President Gilbert Levin for what he calls "an entirely new but simple idea in producing nonfattening sweetners."

Levin calls his invention "left-handed sugar" of L-sugar for short.

Its chemical compenents are identical to ordinary sugar, and it tastes just was sweet, but it can't be digested by human beings, so it doesn't make you fat, doesn't give you tooth decay and can be consumed by diabetics, said Manja Blazer, a senior scientist in Levin's Rockville laboratory.

The patent says the products "have no bitter and objectional aftertaste" and "practically the same physical properties and appearance as the normal sugars used as sweeting agents."

The sugar is called "left-handed" sugar because its molecules are arranged in a mirror image of conventional sugar, she explained. The left-handed sugars occur rarely in nature, and the body can't absorb them in the same way it does the common right-hand variety.

When the enzymes in the body encounter left-handed sugars, "'it's like trying to fit your left hand into a right-handed glove," Levin explained. "The glove can't accept the hand."

Because the body can't metabolize the sugar, it effectively has no calories, passing through the body unchanged, Blazer said. "The advantage over saccharin is the L-sugar is a natural product, it's chemically identical to regular sugar."

No calorie, left-handed sugars can be made from the right-handed, fattening kind but that has never been done on a commercial scale, Blazer said -- one problem that must be solved before the product can be solved before the product can be used in foods and beverages.

The other roadblock is the Food and Drug Administration, which must approve any new food additive. Biospherics has not yet begun the complex testing necessary to prove the product is safe for human consumption, Blazer said. What scientific research has been done on the little-known chemicals indicates they "are probably safe for humans," she added.

The FDA has resisted for several years approving the use of another promising sugar substitute developed by G.D Searle & Co. and could insist on extensive testing of the Biospherics invention.

Levin's patent describes left-handed versions of several different kinds of sugars. Blazer said the most promising kind for food use appears to be left-handed fructose or corn sugar.

Fructose is sweeter than table sugar, or sucrose, and cheaper to produce. In the past couple of years, soft-drink makers have switched to corn sugar to replace the cane or beet sugar in beverages such as Coca-Cola and Pepsi.

Blazer said Biospherics is studying whether to form a joint venture with a bigger company to develop no-calorie sugar or to license its patent to another firm for development.

Levin has worked with left-handed sugars for years and first tried to patent his work in 1976, Blazer said. After additional research and revision of his applications, the pioneer patent was issued on April 15.

Biospherics officials said they believe the market is ripe for an alternative to artificial sweetners because of the growing concern that they may cause cancer. Starting in July all foods containing carcinogens will have to carry health warning labels.