Intracellular localization of posttranslational modifications in the synthesis of hydroxyproline-rich glycoproteins. Peptidyl proline hydroxylation in maize roots

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Abstract
The enzyme prolyl hydroxylase which is responsible for the hydroxylation of peptidyl proline has been investigated in extracts of maize roots. The optimum conditions under which this enzyme can be assayed have been determined using both a colorometric and a radiochemical assay. The enzyme has certain features in common with vertebrate prolyl hydroxylase (pH optimum, requirement for ferrous ion, inhibition by tricine and phosphate buffers, stimulation by bovine serum albumin) but prefers poly-L-proline to collagenous substrates. Centrifugation studies shows that the enzyme is mainly membrane-bound and is primarily localized in the endoplasmic reticulum, although the presence of small amounts in the Golgi apparatus cannot be ruled out.