X-ray texture analysis indicates downward spinning of chitin microfibrils in tubeworm tube

The direction of β-chitin deposition in the tube of tubeworm Lamellibrachia satsuma was investigated by texture analysis using X-ray diffraction. The β-chitin crystallite in the tube has planar orientation with the (1 1 0) plane perpendicular to the surface, and the c-axis is aligned parallel to the tube. The monoclinic unit cell of β-chitin allowed determination of the sense of c-axis from the orientation of (0 1 0) and (1 0 0) planes. This means that the reducing end of β-chitin is pointing up in the tube. This orientation can be ascribed to possible secretion mechanisms of the β-chitin microfibrils, i.e. the chitin-synthesizing enzyme complex travels unidirectionally from top to bottom when the worm body contracts in the tube.