Distribution of Chitinolytic Enzymes in the Organs and cDNA Cloning of Chitinase Isozymes from the Stomach of Two Species of Fish, Chub Mackerel (iScomber japonicus/i) and Silver Croaker (iPennahia argentata/i)

摘要

Chitinolytic activities were measured in two fish species having different feeding habits, chub mackerel (Scomber japonicus) and silver croaker (Pennahia argentata). Chitinase (an endo-type chitinolytic enzyme) activity was measured using pNP-(GlcNAc)n (n = 2, 3) as substrates;its level was significantly high in the stomachs of both species, as well as in the gills, intestine, pyloric appendage, testis, and liver of chub mackerel and in the spleen, kidney, pyloric appendage, ovaries, heart, and liver of silver croaker. β-N-Acetylhexosaminidase (an exo-type chitinolytic enzyme) activity was measured using pNP-(GlcNAc) as a substrate;it was detected at high levels in many parts apart from the digestive tracts of both species. The optimum pH for chitinase activity was 3.0 - 5.0 in the stomachs of both species, 4.0 in the liver of chub mackerel, and 4.0 and 8.0 in the kidney of silver croaker. Full-length cDNAs encoding two chitinase isozymes were obtained from the stomachs of the two fish species: SjChi-1 (1604 bp) and SjChi-2 (1512 bp) from chub mackerel and PaChi-1 (1630 bp) and PaChi-2 (1606 bp) from silver croaker. Expression analysis of these genes in the organs of the two species revealed strong expression of SjChi-1 in the stomach of chub mackerel and that of PaChi-1 andPaChi-2 in the stomach of silver croaker. The difference in the expression pattern of these genes is likely attributed to the difference in the feeding habits of the two fish species. Our results suggested the presence of novel chitinases in the two species.