Alkaline ceramidases

Very recently, two yeast (5. cerevisiae) alkaline ceramidases, phytoceramidase (YPClp) and dihydroceramidase (YDClp), were cloned and partially characterized by Mao et al (2000a, b). YPClp was cloned as a high copy suppressor of the growth inhibition by FBI as it has fumoitisin resistant ceramide synthase activity. The second alkaline ceramidase, YDClp was identified by sequence homology to YPClp. 

YPClp and YDClp have different substrate specificity such that YPClp prefers phytoceramide (phytoCer) over dihydroceramide (dhCer) whereas YDClp prefers dhCer over phytoCer, however, neither enzyme uses the most common mammalian type ceramide having a 4-5 trans double bond on the sphingoid base as substrate. Both enzymes have a narrow pH optimum of 9.4-10, hence, are classified as alkaline ceramidases. Calcium ions activate but are not absolutely required for the activities of both enzymes. and inhibit the activities of both enzymes. None of the sphingoid bases inhibit the activities of YPC Ip and YDClp. 

A database search reveals that YPClp and YDClp are not homologous to any proteins with known functions, but are homologous to putative proteins from Arabidoposis, C. elegans, peptides deduced from EST sequences of human, mouse, pig, zebra fish, and human genomic sequences. A human homologue has been identified and its cDNA has been cloned. Preliminary results show that this human homologue is also an alkaline ceramidase that selectively hydrolyzes phytoCer. 

The physiological roles of the yeast (and their human homologues) alkaline ceramidases are yet to be established. Since these enzymes regulate a series of bioactive lipids such as ceramide, sphingosine, and sphingosine-1-P, we predict that they have an important role in cell regulatory events. 

Kita, K., Okino, N., and Ito, M., 2000, Reverse hydrolysis reaction of a recombinant alkaline ceramidase of Pseudomonas aeruginosa. B/oc/t/m. Biophys. Acta. 1485 111-120. 

Mao, C., Xu, R., Bielawska, A., and Obeid, L.M., 2000a, Cloning of an alkaline ceramidase from Saccharomyces cerevisiae. An enzyme with reverse (CoA-independent) ceramide synthase achvity. J. Biol. Chem., 275 6876-6884. 

Okino, N., Ichinose, S., Omori, A., Imayama, S., Nakamura, T., Ito, M., 1999, Molecular cloning, sequencing, and expression of the gene encoding alkaline ceramidase from Pseudomonas aemginosa. Cloning of a ceramidase homologue from Mycobacterium tuberculosis. J. Biol. Chem. 274 36616-36622. 

Tani, M., OMno, N., Mori, K., Tatiigawa, T., Izu, H. and Ito, M., 2000, Molecular cloning of the fuU-length cDNA encoding mouse neutral ceramidase. A novel but highly conserved gene family of neutral/alkaline ceramidases,/. Biol. Chem. 275 11229-11234. 

SM Precursor of ceramide Acid/neutral/alkaline ceramidase enzymatic activity ... 

D-MAPP Neutral/ Alkaline ceramidase inhibitor Squamous cell carcinoma... 

Sugita, M., Williams, M., Dulaney, J., and Moser, H. (1975). Ceramidase and ceramide synthesis in human kidney and cerebellum. Description of a new alkaline ceramidase. Biochim. Biophys. Acta 398, 125-133. 

Alkaline ceramidase D-MAPP ((lS,2 )-A-myristoyl-2-amino-1 -phenyl-1 -propanol) Bielawskaef aZ., 1996... 

---