ISOLATION AND PARTIAL CHARACTERIZATION OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) GILL MUCIN

Gill mucin from rainbow trout was isolated utilizing two rounds of ces ium chloride density ultracentrifugation followed by gel filtration on Sepharose CL-2B. Neither density ultracentrifugation nor gel filtrati on alone was sufficient for purification of the mucin. Isolated gill m ucin had a density of 1.5 g/ml and eluted at the void volume of the Se pharose CL-2B column. Silver-stained reducing 6% polyacrylamide gel el ectrophoresis of gill mucin produced a band at the origin with a smear entering the separating gel. There was no evidence of a link protein in gill mucin on reducing 12% polyacrylamide gel electrophoresis. Gill mucin had an amino acid profile similar to that of mucins in other sp ecies. Specifically, 35.1% of the total amino acids were represented b y threonine and serine, while another 27.5% were alanine and proline. Gill mucin contained galactose (26.7 +/- 3.2%), galactosamine (22.5 +/ - 4.4%), glucose (16.6 +/- 8.7%), fucose (16.1 +/- 1.5%), glucosamine (12.0 +/- 1.9%) and mannose (5.1 +/- 4.4%). Uronic acid levels from pu rified mucin were very low (0.7 +/- O.1%). Sialic acid was also presen t (0.06 g/g of mucin protein). The periodic acid-Schiff assay routinel y utilized for detection of mucins was relatively insensitive for dete ction of gill mucin (6 x less sensitive than for pig gastric mucin) so a rabbit antiserum was raised. The antiserum produced profiles simila r to the periodic acid-Schiff assay of fractions following gel filtrat ion. Immunofluorescence of formalin-fixed rainbow trout gill tissue se ctions showed that the antiserum detected mucin within branchial goble t cells.