The bulk hydrophobic character for the 20 natural amino acid residues, has been obtained from a database of 60 protein structures, grouped in the four structural classes alpha alpha, beta beta, alpha + beta and alpha/beta. The hydrophobicity coefficients thus obtained are compared with Ponnuswamy's original values using scales normalized to average = 0.0 and standard deviation = 1.0. Even though most of the amino acid residues do not change their hydropathic character in the different structural classes, their behaviour suggests the convenience that averaging methods should only consider proteins of the same structural class and that this information should be included in the secondary structure methods.

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Conformations associated with secondary structure in human salivary proline-rich proteins A (PRPA), C (PRPC), P-D and P-E were predicted by analysis of their respective hydrophobicity profiles by computer programming. Structurally, PRPA and PRPC would present a globular head and a tail that consists of type 3,, polyproline helices. P-D and P-E would be fibrilar molecules with helical zones of the polyproline 3,, type. Alternatively for PRPA and PRPC, the head and tail would form one globular domain with the tail folding upon itself at places where random coils occur.

A 3-dimensional model, common for the secondary structures of four fl-lactamases obtained from Escherichia coli, Bacillus licheniformis, Bacillus cereus and Staphylococcus aureus, is proposed. The predictions of the structures were made by the hydrophobicity profiles method complemented by the modified Chou and Fasman's method. The model proposed presents 56% constancy and can be described as a 2-domain structure, in agreement with low resolution X-ray data reported for the E. coli enzyme. The model would explain how a common function can be performed by enzymes of very different sizes, composition and sequence. fl-LactamaseSecondary structure prediction