Identification and purification of collagen-synthesizing polysomes with anti-collagen antibodies

Antibodies against embryonic chick bone collagen were prepared in rabbits and were purified by affinity and ion exchange chromatography until collagen-specific and RNase-free. 125I-anti-collagen antibodies were used to locate the collagen-synthesizing polysomes of 8-day chick embryo wings and legs on sucrose gradients by measuring the polysome associated radioactivity. The 125I-anti-collagen antibodies bound predominantly to polysomes in the heavy region of sucrose gradients. These binding sites could only be saturated with homologous anti-collagen antibodies. Further evidence for the specificity of this reaction was provided by a correlation of the amount of anti-collagen antibodies bound in the heavy regions of sucrose gradients with the amount of collagen being synthesized by a particular tissue. The validity of this immunochemical method was confirmed by localizing collagen-synthesizing polysomes by an independent method which utilizes their ability to incorporate [3H]proline into collagen peptides in a cell-free system. The collagen-synthesizing polysomes are found in a single, rather broad peak in these gradients. The results of shortening the centrifugation time indicate that larger species of collagen-synthesizing polysomes are not present in these tissues. Partial purification of the collagen-synthesizing polysomes may be achieved by specifically sedimenting them after treatment with anti-collagen antibodies followed by goat anti-rabbit antibodies.