Vasorelaxant Effect of 5'-Methylthioadenosine Obtained from Candida utilis Yeast Extract through the Suppression of Intracellular Ca(2+) Concentration in Isolated Rat Aorta

Our study is the first to demonstrate the vasorelaxant effect of Candida utilis yeast extract on rat aorta (EC50 of 7.2 ± 3.2 mg/mL). Among five identified compounds, 5'-methylthioadenosine (MTA) exhibited comparable vasorelaxant effect (EC50 of 190 ± 40 μM) with adenosine, a known vasodilator, on 1 μM phenylephrine (PE)-contracted Sprague-Dawley rat aortic rings. MTA induced vasorelaxation in an endothelium-independent manner and independent of the adenosine receptors. MTA reduced a CaCl2-induced vasocontraction stimulated by 1 μM PE, whereas the effect was abolished in a 60 mM KCl-induced vasocontraction. This indicates that MTA was not involved in the suppression of extracellular Ca(2+) influx. MTA significantly (P < 0.01) attenuated the PE-induced activation of calmodulin-dependent kinase II (CaMK II) in aortic rings and inhibited the phosphorylation of L-type Ca(2+) channel (VDCC). In conclusion, the underlying mechanism(s) of MTA-induced vasorelaxation involves the inhibition of Ca(2+)/CaMK II/VDCC phosphorylation pathway, resulting in the suppression of intracellular Ca(2+) concentration in aortic rings.

Molecular cloning and nucleotide sequence of the 3-isopropylmalate dehydrogenase gene of Candida utilis

A 3-isopropylmalate dehydrogenase (3-IMDH, EC 1.1.1.85) gene was cloned from a gene library of Candida utilis. One of the plasmids, pYKL30, could complement Escherichia coli leuB and Saccharomyces cerevisiae leu2 auxotrophs; a 2.2 kb HindIII fragment subcloned in pBR322 could still complement the leuB mutation. Southern hybridization confirmed that this fragment was derived from C. utilis. An open reading frame of 1089 bp that corresponded to a polypeptide of 363 amino acids, one residue shorter than the 3-IMDH of S. cerevisiae, was found in the cloned fragment. The homology between the 3-IMDHs of C. utilis and S. cerevisiae was 76.2% in nucleotides and 85.4% in amino acids. In contrast, the homology between the 3-IMDHs of C. utilis and Thermus thermophilus was much smaller and was restricted to some regions of the gene.