Epimerization of trans-4-hydroxy-L-proline to cis-4-hydroxy-D-proline during acid hydrolysis of collagen.

1. trans-4-Hydroxy-r,-proline is epimerized to &+hydroxy-n-proline under the conditions generally used for the hydrolysis of proteins for analyses of amino acids. 2. The cis epimer elutes from a column of UR-30 resin on a Beckman amino acid analyzer at the same time as threonine and hence would be undetected. 3. About 8% of the trans-4-hydroxy-L-proline in collagen can be epimerized to c&4-hydroxy-n-proline in the hydrolysis of collagen with 6 N HCl at 110” for 72 hr. 4. A procedure is described whereby the primary amino acids in hydrolyzates are deaminated with nitrous acid and removed so that the amounts of truns-4-hydroxyproline, cis-4-hydroxyproline, and proline can be determined without changing the temperature of the column of UR-30 resin on the Beckman amino acid analyzer.