Methanogens membrane-bound enzymes

The following data indicate that CH3-H4MPT H-S-CoM methyltransferase is the site of primary Na translocation (see Figs. 6 and 12) (i) the enzyme has been partially purified from Methanosarcina barkeri and Methanobacterium thermoautotrophicum and found to be tightly membrane bound [69b] (ii) inverted vesicles of the methanogenic strain G61 catalyzed methyl transfer from CH3-H4MPT to H-S-CoM. This reaction was stimulated by Na ions and was coupled with the accumulation of Na" into the vesicles. Na uptake was inhibited by Na ionophores rather than by protonophores indicating primary Na translocation [168]. 

A characteristic of virtually all methanogen hydrogenases is their very large native size (although they are soluble enzymes), typically 600-1000 kDa. This is often explained as a result of hydrophobic interactions with other proteins, and as an indication that it is a loosely-bound membrane protein. H2ase is often associated with membranes early during its purification [271,280]. These properties have been investigated in several ways by electron microscopy. 

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