Catalyzes the reduction of dihydromethanopterin (H(2)MPT) to tetrahydromethanopterin (H(4)MPT). Shows preference for NADPH rather than NADH as electron donor. Does not reduce dihydrofolate. 5,6,7,8-tetrahydromethanopterin + NAD(+) = 7,8-dihydromethanopterin + H(+) + NADH 5,6,7,8-tetrahydromethanopterin + NADP(+) = 7,8-dihydromethanopterin + H(+) + NADPH Optimum pH is 5.3. Optimum temperature is 30 degrees Celsius (at pH 5.3). Cofactor biosynthesis; 5,6,7,8-tetrahydromethanopterin biosynthesis. Homodimer. Mutants have a C1-defective and methanol-sensitive phenotype.