Description_x000D_ General description_x000D_ Collagen type I is present in soft connective tissues and bone, where it constitutes more than 90% of the organic matrix.1 During bone formation collagen type I is synthesized from pro-collagen type I, which is secreted from fibroblasts and osteoblasts.2 Pro-collagen type I contains N-and C-terminal extensions, which are removed by specific proteases during the conversion of procollagen to collagen.3 Measurements of N- terminal propeptides of procollagen type I (PINP) can be of value in assessing bone formation. Recent evidence indicates that PINP can serve as a serum biomarker of bone formation, as it accurately identifies those patients who are responding to anabolic or antiresorptive therapy within 3 months of the start of treatment.4 The use of this biomarker in patients being treated for osteoporosis may significantly improve therapy adherence and clinical outcomes.4_x000D_ Immunogen_x000D_ QEEGQVEGQDEDIPPITCVQNGLRYHDRDVWKPEPCRICVCDNGKVLCDDVICDETKNCPGAEVPEGECCPVCPDGSESPTDQETTGVEGPKGDTGPRGPRGPAGPPGRDGIPGQPGLPGPPGPPGPPGPPGLGGNFAPDYKDDDDKGHHHHHHHHGGQ_x000D_ Biochem/physiol Actions_x000D_ SILu™Lite COL1A1 recombinant human protein expressed in human 293 cells. It is a protein of 159 amino acids (Q23-P161 and including C-terminal polyhistidine and FLAG® tags) with a calculated molecular mass of 16 kDa. SILu Lite COL1A1 is an analytical standard designed to be used as starting material for preparation of calibrators and controls in LC-MS applications._x000D_ Physical form_x000D_ Lyophilized from a solution of phosphate buffered saline._x000D_ Legal Information_x000D_ FLAG is a registered trademark of Sigma-Aldrich Co. LLC_x000D_ SILu is a trademark of Sigma-Aldrich Co. LLC