Studies on bound trans-4-hydroxy-L-proline in sandal (Santalum album L.)

1. trans-4-Hydroxy-l-proline was found to occur in the bound state in the leaves of sandal (Santalum album L.), in which large amounts of free cis-4-hydroxy-l-proline are also present. 2. Bound trans-4-hydroxy-l-proline was present, associated mainly with a ;wall' fraction and a ;soluble' fraction roughly in equal proportions. 3. Bound proline is present only in small amounts in the ;soluble' fraction but is mostly associated with the ;wall' fraction and the other sedimented fractions. 4. In the free amino acid fraction more than 98% of the hydroxyproline had the cis-configuration, whereas in the ;wall' and ;soluble' fractions more than 90% of the bound hydroxyproline was in the trans-configuration. 5. Various extraction procedures indicated heterogeneity of the hydroxyproline-containing components. Hot 5% (w/v) trichloroacetic acid extracts about 25% of hydroxyproline and m-NaOH extracts an additional 25%. 6. Incorporation of [(14)C]proline into the bound hydroxyproline was demonstrated. The hydroxyproline component of the ;soluble' fraction does not appear to be the precursor of that of the ;wall' fraction.