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We have reported previously that the ceramidase from Pseudomonas aeruginosa AN17 isolated from a patient with atopic dermatitis requires detergents for hydrolysis of ceramide (Cer) [Okino, Tani, Imayama and Ito (1998) J. Biol. Chem. 273, 14368–14373]. In the present study, we report that some glycerophospholipids strongly activated the hydrolysis of Cer by Pseudomonas ceramidase in the absence of detergents. Among the glycerophospholipids tested, cardiolipin was most effective in stimulating hydrolysis of Cer followed by phosphatidic acid, phosphatidylethanolamine and phosphatidylglycerol, whereas phosphatidylcholine, lysophosphatidic acid and diacylglycerol were less effective. Interestingly, Staphylococcus aureus-derived lipids, which contain cardiolipin and phosphatidylglycerol as major lipid components, also strongly enhanced the hydrolysis of normal Cer, as well as the human skin-specific ω-hydroxyacyl Cer, by the enzyme in the absence of detergents. It was confirmed that several strains of P. aeruginosa, including AN17, secrete a significant amount of staphylolytic proteases to lyse S. aureus cells, resulting in the release of cardiolipin and phosphatidylglycerol. Since both P. aeruginosa and S. aureus are suspected of being present in microflora of atopic skin, we speculate that S. aureus-derived glycerophospholipids stimulate the hydrolysis of Cer in atopic skin by bacterial ceramidase.

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A variety of long-chain fatty acylamino analogs of N-acetylmuramoyl-L-alanyl-D-isoglutamine (MDP), such as A^-(acyl)muramoyl-dipeptides(1) and Af-acetyl-6-(acylamino)-6-deoxymuramoyldipeptides (2), were synthesized to examine their immunological activities.(1) were active as adjuvant on the induction of delayedtype hypersensitivity to azobenzenearsonate-7V-acetyl-L-tyrosine in guinea pigs. A^-(3-Hydroxy-2- Recently, we have found that the 2-amino group of the carbohydrate moiety in MDPcan be acylated by myristoyl, stearoyl, 3-hydroxymyristoyl and 3-hydroxystearoyl groups1} instead of the acetyl group without decreasing the activity. In this paper, we describe the synthesis and immunological activities of N-(acyl)muramoyl-dipeptides (lb~lf) and 7V-acetyl-6-(acylamino)-6-deoxymuramoyldipeptides (2A~2C) bearing other long-chain fatty-acyl residues as the lipophilic group. We also discuss the effect of the alkyl-chain length of the iV-acyl moiety for the adjuvant activity.