Natural substances vs patentable inventions
Yet, subtly and without fanfare, the prohibition on patenting products of nature has fallen into legal disuse. The US Patent and Trademark Office and federal courts now routinely issue patents on discovered natural substances if they are "isolated and purified" or otherwise (insubtantially) modified. Naturally-occurring DNA and protein molecules have, consequently, become the subject of thousands of patent applications.
In this article, Linda J Demaine and Aaron X Fellmeth describe the "Substantial Transformation Test", a method designed to distinguish products of nature from patentable inventions.
Link to Science article
Reference: Science 300, 1375 (2003)