Derivatives of methanopterin, a coenzyme involved in methanogenesis

Abstract

Degradational studies of methanopterin, a coenzyme involved in methanogenesis, are reported. The results of these studies are in full accordance with the proposed structure of methanopterin as N‐[1′‐(2″‐amino‐4″‐hydroxy‐7″‐methyl‐6″‐pteridinyl)ethyl]‐4‐[2′,3′,4′,5′‐tetrahydroxypent‐1′‐yl(5′‐1″)O‐α‐ribofuranosyl‐5″‐phosphoric acid] aniline in which the phosphate group is esterified with α‐hydroxyglutaric acid. Acid hydrolysis of methanopterin cleaved the 5′→ 1″ glycosidic bond and yielded a ‘hydrolytic product’ which was identified as N‐[1′‐(2″‐amino‐4″‐hydroxy‐7″‐methyl‐6″‐pteridinyl)ethyl]‐4‐[2′, 3′,4′, 5′‐tetrahydroxypent‐1′‐yl]aniline. Alkaline permanganate oxidation of methanopterin yielded 7‐methylpterin‐6‐carboxylic acid. Catalytic (or enzymatic) hydrogenation of methanopterin gave a mixture of 6‐ethyl‐7‐methyl‐7,8‐dihydropterin, 6‐ethyl‐7‐methylpterin and a third compound, named methaniline which was identified as 4‐[2′, 3′,4′,5′‐tetrahydroxypent‐1′‐yl(5′→ 1″)O‐α‐ribofuranosyl‐5″‐phosphoric acid]aniline, in which the phosphate group is esterified with α‐hydroxyglutaric acid. Methanosarcina barkeri contains a closely related coenzyme called sarcinapterin, which was identified as a l‐glutamyl derivative of methanopterin, where the glutamate moiety is attached to the α‐carboxylic acid group of the α‐hydroxyglutaric acid moiety of methanopterin via an amide linkage.

Biosynthesis of Methanopterin in Methanobacterium thermoautotrophicum

“…7) with phosphoribosylpyrophosphate (10) under decarboxylation. The adduct 13 could then be reduced via the quinoid form 14 leading to the ribityl aniline moiety of methanopterin.…”

“…5). Similarly, the labeling patterns of phosphoribosylpyrophosphate (10) and a-ketoglutarate (11) are reflected in ribonucleosides and glutamate, respectively (Fig. 5).…”

“…1 from dehydrogenation of the coenzyme, was fIrst isolated from M thennoautotrophicum (8), and its structure has been elucidated by two-dimensional spin-echo correlation NMR spectroscopy (SECSy), Nuclear Overhauser spectroscopy (NOESy), and IH_ l3C shift-correlated experiments (9). An L-glutamyl derivative of methanopterin, sarcinapterin (2), has been isolated from Methanosarcina barken (10). More recently, an aspartyl derivative and a 7-demethyl derivative of sarcinapterin (tatiopterin; 3) has been found in Methanogenium tationis ( Fig.…”

Partial purification and characterization of F₄₂₀-dependent NADP reductase from Methanobrevibacter smithii strain DE1

“…aniline, is present in all known methanogens, and it and many of its derivatives are important in methanogenesis [26]. Methanopterin itself, may be a species which occurs as an artifact of purification, and a direct role for it in methanogenesis has not been established.…”

“…However, one of its derivatives, tetrahydromethanopterin, also called formaldehyde activation factor (FAF), appears to be a carbon carrier at the formyl, methenyl, and methyl levels of oxidation [27,28,29,30]. This is not surprising, since methanopterin bears a structural resemblance to folic acid, which participates in other well known metabolic processes as tetrahydrofolate and other derivatives, Other compounds found with or associated with methanopterin and FAF may be artifacts caused by the breakdown of the unstable and easily oxidized FAF [24,26,31]. The structure of methanopterin is shown in and has long been identified as being involved with the binding of a methyl group with a subsequent demethylation yielding methane [5].…”