ISSN:
1432-1327
Keywords:
Key words Hydrogenases
;
catalytic mechanisms
;
para-ortho hydrogen conversion
;
carbocations
;
methanogenic Archaea
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract H2–forming N 5,N 10 –methylenetetrahydromethanopterin dehydrogenase is a novel type of hydrogenase that contains neither nickel nor iron-sulfur clusters. Evidence has been presented that the reaction mechanism catalyzed by the enzyme is very similar to that of the formation of carbocations and H2 from alkanes under superacidic conditions. We present here further results in support of this mechanism. It was found that the purified enzyme per se did not catalyze the conversion of para H2 to ortho H2, a reaction catalyzed by all other hydrogenases known to date. However, it catalyzed the conversion in the presence of the substrate N 5,N 10 –methenyltetrahydromethanopterin (CH≡H4MPT+), indicating that for heterolytic cleavage of H2 the enzyme-CH≡H4MPT+ complex is required. In D2O, the formation of HD and D2 from H2 rather than a para–ortho H2 conversion was observed, indicating that after heterolytic cleavage of H2 the dissociation of the proton from the enzyme-substrate complex is fast relative to the re-formation of free H2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s007750050077
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