PubMed · 171372
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S G Frank. 1975. Inclusion compounds.. https://doi.org/10.1002/jps.2600641003
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Xanthomonas oryzae pv. oryzae is a bacterial pathogen that causes leaf blight, a serious disease of rice. Most members of the genus Xanthomonas produce yellow, membrane bound, brominated aryl polyene pigments called xanthomonadins whose functional role is unclear. We find that pigment-deficient mutants of X. oryzae pv. oryzae exhibit hypersensitivity to photobiological damage. A clone containing the xanthomonadin biosynthetic gene cluster alleviates the hypersensitivity of the pigment-deficient mutant. Extracts containing xanthomonadin provide protection against photodynamic lipid peroxidation in liposomes. These results lead us to suggest a role for the pigment, namely protection against photodamage.
Despite the importance of the substrate 4-hydroxyanisole in melanoma therapy, the kinetics of its oxidation catalyzed by tyrosinase has never been properly characterized. This approach is reported here for the first time. The applicability to 4-hydroxyanisole of the reaction mechanism of tyrosinase previously proposed for other monophenols has been corroborated. The Michaelis constant for the oxidation of 4-hydroxyanisole catalyzed by mushroom tyrosinase was (62 +/- 1.5) microM at pH 7 and increased when the pH decreased, reaching a value of (195 +/- 5) microM at pH 5.5. However the maximum steady-state rate, whose value was (0.54 +/- 0.01) microM/min, did not change with the pH. The apparent catalytic constant was (184 +/- 5) s-1, around twenty three times higher than that previously described for L-tyrosine (8 s-1).
p-Methoxyphenyl (pMP) beta-D-glycopyranosides (Glc, Gal, GlcNPhth, GalNPhth, GlcNTroc, Gal beta 4Glc, Gal alpha 4Gal) were prepared from the corresponding 1-O-acetyl sugars in 79-90% yield, using boron trifluoride etherate as promoter. Treatment of the pMP glycosides with acyl chlorides or bromides in the presence of various Lewis acids gave the corresponding glycosyl chlorides and bromides in 81-98% yield. Treatment of the acyl-protected pMP glycosides with thiophenol and boron trifluoride etherate gave the corresponding thioglycosides in 80-100% yield and high (> 20:1) beta/alpha selectivity. The stability of pMP glycosides was investigated against a series of reagents.