During the formation of hydroxyproline and hydroxylysine, the essential factors required is/are

In Collagen Synthesis: Vitamin C is required for the post-translational modification, Hydroxylation of lysine and Proline Vitamin C plays the role of a coenzyme The hydroxylation reaction is catalysed by lysyl hydroxylase (for lysine) and prolyl hydroxylase (for proline) this reaction is dependent on vitamin C(ascorbic acid), molecular oxygen and alpha-ketoglutarate Hydroxyproline and hydroxylysine are essential for the collagen cross-linking and the strength of the fibre Ref: Satyanarayana 4th ed page 132