BACTERIAL-MEMBRANES - POSSIBLE SOURCE OF A MAJOR DISSOLVED PROTEIN INSEAWATER

We have measured dissolved protein at a variety of depths at three sta tions in the Pacific, ranging from the tropics to the subarctic, Most of the dissolved protein at these stations is distributed over a wide range of molecular masses, but consists of fewer than thirty individua l proteins. One, with an apparent molecular mass of 48 kDa, is a major constituent at all stations. Its N-terminal amino acid sequence was f ound to be a homologue of porin P, a trans-outer-membrane channel prot ein of Gram-negative bacteria, Correspondence of N-terminal amino acid sequences and apparent molecular masses between this dissolved protei n and porin P indicates that almost the complete homologue of porin P, from the N-terminus to (probably) the C-terminus, survives without mo dification in the water column. Persistence of appreciable amounts of an identifiable protein suggests a pathway for production of dissolved organic matter whereby enzyme-resistant biopolymers survive and accum ulate in the sea.