Structure of Protocollagen Proline Hydroxylase from Chick Embryos

Protocollagen proline hydroxylase was purified from chick embryos with an affinity‐column procedure which yielded pure enzyme in a tetramer form. Electron microscopy of the enzyme after it was largely dissociated into monomers indicated that the monomers were rod‐shaped with a diameter of 3.31 ± 0.07 nm (S.E.M.) and a length of 6.95 ± 0.07 nm. In preparations of the enzyme in which the protein was partially dissociated, dumb‐bell and V‐shaped structures were seen which morphologically consisted of two sub‐structures each with dimensions similar to those of the isolated monomers. The results suggested that these structures were dimers in which the monomers were joined at one end with an angle between their longitudinal axes. The largest regular protein structures seen in preparations of the enzyme were about 8 × 8 nm and in some of these structures four sub‐structures were seen, indicating that they were tetramers. On the basis of the data presented here we propose a model of the tetramer in which two V‐shaped dimers were interlocked. Further studies demonstrated that the single‐ring and four‐ring structures seen by electron microscopy of enzyme preparations obtained by a previous purification procedure were not the enzyme.