Random mutagenesis was used to enhance the thermal stability of Streptomyces cholesterol oxidase. Four thermostable mutants were isolated and the following amino acid substitutions were identified: Ser103 to Thr (mutant S103T), Val121 to Ala (mutant V121A), Arg135 to His (mutant R135H) and Val145 to Glu (mutant V145E). The wild-type and mutant enzymes were purified and characterized. The properties of mutants S103T, V121A and R135H were similar to those of the wild type but they showed improved thermal stability. When the V145E mutation was introduced, the thermal stability of the enzyme was markedly increased and the optimum pH was desirably changed to encompass a broad range from acid to alkali. Analysis of multiple mutants constructed by site-directed mutagenesis showed that all the mutations except that of R135H had an additive influence on the other mutations. These mutational effects are discussed in terms of a three-dimensional structural model of the enzyme constructed on the basis of homology modelling.

The effects of seaweed diets on the lipid and fatty acid (FA) composition of juvenile abalone Halio tis discus hannai were investigated by feeding seaweeds with different FA profiles: green (Ulva pertusa, rich in 16:4n-3, 18:3n-3, and 18:4n-3 polyunsaturated fatty acids or PUFAs), red (Grateloupia sparsa, high in 20:4n-6 and 20:5n-3 PUFAs), and brown (Undaria pinnatifida, rich in 18:3n-3, 18:4n-3, 20:4n 6, and 20:5n-3 PUFAs), in a 66-day feeding trial. The best growth was observed in juveniles fed U. pin natifida. None of the seaweed diets affected the major lipid classes of abalone tissues. The PUFAs, 16:4n-3, 20:5n-3, and 22:5n-3 were major FAs of abalone tissues even if these were undetected or found only in very small amounts in the seaweed diet, suggesting their synthesis from dietary n-3 series of low er fatty acids. The poor growth rates were associated with seaweed diets deficient in 18:2n-6, 18:3n-3, 18:4n-3, or 20:4n-6.

Four semi-purified diets, containing crystalline amino acids (CAAs), were fed to juvenile red sea bream, Pagrus major in order to ascertain the ideal dietary amino acid pattern for this species. A control diet containing 50% casein-gelatin as protein sources, but no CAAs were fed to the fish. The other diets contained 30% casein-gelatin and 20% CAAs. CAAs were added to diets to simulate with amino acid pattern of the red sea bream eggs protein (REP), red sea bream larvae whole body protein (RLP), red sea bream juvenile whole body protein (RJP), and brown fishmeal protein (BFP). The juveniles (average initial body weight, 1.58 ± 0.01 g) were maintained in triplicate tanks and fed twice daily for 30 days. The highest weight gain was observed in juveniles fed the RJP diet. No significant difference was observed in juveniles fed the RLP and BFP diet. Feed efficiency ratio, protein efficiency ratio and amino acid retention in the whole body were significantly (p < 0.05) affected by the simulated dietary amino acid patterns. The essential amino acid profile and A/E ratios of the whole body after the growth trial showed little difference among the dietary treatments. The results suggest that red sea bream juveniles are able to utilize high amounts of CAA in coated form. The amino acid pattern of RJP could be used as an appropriate of reference dietary amino acid for this species.

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