The peptide NK-2 is an effective antimicrobial agent with low hemolytic and cytotoxic activities and is thus a promising candidate for clinical applications. It comprises the ␣-helical, cationic core region of porcine NK-lysin a homolog of human granulysin and of amoebapores of pathogenic amoeba. Here we visualized the impact of NK-2 on Escherichia coli by electron microscopy and used NK-2 as a template for sequence variations to improve the peptide stability and activity and to gain insight into the structure/ function relationships. We synthesized 18 new peptides and tested their activities on seven Gram-negative and one Gram-positive bacterial strains, human erythrocytes, and HeLa cells. Although all peptides appeared unordered in buffer, those active against bacteria adopted an ␣-helical conformation in membrane-mimetic environments like trifluoroethanol and negatively charged phosphatidylglycerol (PG) liposomes that mimick the cytoplasmic membrane of bacteria. This conformation was not observed in the presence of liposomes consisting of zwitterionic phosphatidylcholine (PC) typical for the human cell plasma membrane. The interaction was paralleled by intercalation of these peptides into PG liposomes as determined by FRET spectroscopy. A comparative analysis between biological activity and the calculated peptide parameters revealed that the decisive factor for a broad spectrum activity is not the peptide overall hydrophobicity or amphipathicity, but the possession of a minimal positive net charge plus a highly amphipathic anchor point of only seven amino acid residues (two helical turns).

A feeding trial with Macrobrachium acanthurus juveniles was performed to determine growth performance and utilization of diets varying in protein, lipid, and carbohydrate level. Twelve diets were formulated with three levels of protein (P) and supplemented with different proportions of lipids (L) and carbohydrates (C): P30‐L20‐C8, P30‐L15‐C19, P30‐L12‐C25, P30‐L10‐C31, P35‐L20‐C3, P35‐L15‐C15, P35‐L10‐C26, P35‐L5‐C38, P40‐L15‐C8, P40‐L10‐C19, P40‐L5‐C31, and P40‐L1‐C40. Lipids and carbohydrates were added allowing an overall energy content limit of 400 kcal per 100 g of diet. Each diet was fed to triplicate groups of juveniles with an initial weight of 60.9 ± 10.9 mg (mean ± SD) for 60 days. Overall growth performance and gene expression of fatty acid synthase (FAS), carnitine palmitoyltransferase 1 (CPT1), glucose‐6‐phosphatase (G6P), and hexokinase (HK) in the hepatopancreas were assessed. Highest weight gain values and specific growth rates were observed in prawns fed diets with 35% of protein inclusion. Expression of FAS was downregulated when fed 30% of protein. Results indicate M. acanthurus use protein as their primary source of energy and when this is low in the diet, lipids are used to spare the energy from proteins. Suggested inclusion of protein, lipids, and carbohydrates in diets for M. acanthurus should be 35%, 15%, and 15%, respectively.