DIRECT INCORPORATION OF HYDROXYPROLINE INTO AVENA COLEOPTILE PROTEINS

The cis isomer of L-hydroxyproline (allohydroxyproline), when present at a growth-inhibitory level (0.5 mM), is directly incorporated into Avena coleoptile proteins at a rate that is about three times greater than the normal rate of formation of trans-hydroxyproline. This incorporation is predominately into cytoplasmic proteins, is linear with time, and is only slightly affected by 0.15 mM α,α-dipyridyl. The ability of proline to prevent this incorporation suggests that the cis-hydroxyproline is being incorporated into protein in place of proline. Label from [3H]trans- hydroxyproline also appears in protein-bound hydroxyproline, but the bulk of this incorporation appears to be indirect (i.e., through proline) since it can be severely inhibited by dipyridyl. Both isomers of hydroxyproline can be converted to proline by Avena coleoptile tissues, but the trans isomer is more efficiently utilized in this reaction. The lack of correlation between the incorporation of hydroxyproline isomers into protein and their ability to inhibit cell elongation indicates that while the direct incorporation of hydroxyproline into protein may contribute to the inhibition of auxin-induced growth, it is unlikely to be its principal cause. © 1968, American Chemical Society. All rights reserved.