AB-INITIO DIRECT PHASING OF PROTEINS - THE LIMITS

The role of directed methods in the protein field is analyzed. A criterion is formulated which suggests the necessary conditions for the success or the failure of the ab initio direct procedures. The distribution of quantity z = [alpha]/sigma(alpha) is central in our considerations. Most of the experimental protein data do not satisfy such a criterion, therefore their ab-initio solution is a quite improbable event.