Atelocollagen was prepared from salmon nasal cartilage by limited digestion with an acid protease from a fungus Rhizopus niveus, and was referred to as Rhizopus acid protease-solubilized collagen (RSC). More than 60% of total collagen was recovered as RSC by the enzymatic treatment for 48 h at 4 °C. The RSC exhibited a main α-band, corresponding to α1(II) chain, and two minor α-bands with slower mobility than that of the main band on SDS-PAGE. Ammonium sulfate fractionation was applied to the RSC using 0.5 M acetic acid containing 11% (w/v) (NH4)2SO4 to fractionate collagen types in it. The insoluble fraction (P-11) showed SDS-PAGE pattern similar to that of the RSC. Furthermore, the fraction that was soluble at 11% (NH4)2SO4 and then recovered by salting out with 20% (NH4)2SO4 (S-11 fraction) showed three α-bands on SDS-PAGE with a staining intensity ratio of 1:1:1, amino acid composition characteristic of type V/XI collagen family, and relatively poor in alanine and rich in hydroxylysine when compared with vertebrate type I collagens. These results suggested that the S-11 fraction mainly contained Type XI collagen with a chain composition of α1(XI) α2(XI) α3(XI). [ABSTRACT FROM AUTHOR]