Materials and Methods.-Preparation of normal, lathyritic, and lysine-C'4 collagen: Salt-and acid-extracted collagens were prepared from rat skin. 8 Lathyritic salt-extracted skin collagen was obtained from rats ingesting 10 mg of fl-aminopropionitrile (BAPN) daily for three weeks. Salt-and acid-extracted skin collagen was obtained from rats receiving 17, uc of L-lysine-C'4 by injection for each of the 3 days preceding sacrifice. al, a2, and# 12 were prepared from heatdenatured collagens by fractionation on columns of CM cellulose. 3'4, 8 Chromatography: Chromatography was performed on Whatman phosphocellulose (floe, ca-pacity 7.4 m Eq/gm) in a 2.5 X 20-cm column at 40. Approximately 100 mgsamples were applied and the column was eluted at 140 ml/hr with 0.001 M sodium acetate, pH 3.8, on which was superimposed a lineargradient of NaCl from 0 to 0.3 M over a total volume of 820 ml. The effluent was monitored continuously at 230 mgt. Aliquots of radioactive effluent fractions were counted in a planchet counter. Molecular sieve chromatography was performed on a 2 X 40-cm column of Bio-Gel P-2 in ammonium propionate buffer, pH 4.5 (2.24 ml propionic acid and 0.98 ml concentrated NH40H diluted to 1 liter) and eluted under gravity flow at a rate of 46 ml/hr. Cleavage with CNBr: The technique employed has been described. 7 Satisfactory conversion of methionine to homoserine (85-92%) in a chains and f3 components has been achieved by incu-417