story identification - Chirality and Colonists

Trying to identify a very old story that involved human colonists who land on a distant earth-like planet and find human survivors of a much earlier colonizing attempt. The new colonists discover that while their own enzymes are based on common L-isomers, the survivors have evolved and mutated so that their enzymes are R-isomers (L- and R- denote opposite chiralities). It turns out that the food brought by the new colonists cannot sustain the survivors and the planet's natural food supply cannot sustain the new colonists.