Serum protein and non-protein hydroxyproline in patients with rheumatoid arthritis; description of modified method for protein hydroxyproline

Abstract

Our modification of the method of LeRoy, Kaplan, Udenfriend and Sjoerdsma (J. Biol. Chem., 239 (1964) 3350) for determination of protein hydroxyproline in blood serum or plasma is described in detail. The essential modifications consist of conventional hydrolysis by reflux in 6 NHCl and elution in 12 ml of 1 N HCl from the ionexchange resin instead of hydrolysis in 0.24 N Ba(OH) 2 and elution in 20 ml of 1 N. HCl, and data are presented for recovery of added hydroxyproline by the modified method. Values are reported for protein hydroxyproline in serum of two series of 22 and 16 adult patients with classical or definite rheumatoid arthritis which also include results of free, total peptide and glycylprolylhydroxyproline. These are compared with values in normal subjects previously reported by us. There is very infrequent elevation of the values of protein hydroxyproline in our patients, which is markedly different from the result of LeRoy et al.in plasma. This discrepancy is discussed and may indicate that plasma is more suitable for determination of protein hydroxyproline since this protein apparently is formed rapidly in tissues of the reticular endothelial system.