Transhydrogenase (X ZR 115/09)" relates to the use of microorganisms for producing a target substance, wherein the metabolic system of the microorganism is modified "wherein productivity of said microorganism for reduced nicotinamide adenine dinu-cleotide phosphate is enhanced" (cited from original claim 1.
It was known that nicotinamide adenine dinu-cleotide phosphate (NADPH) plays a role in the metabolic system producing the target substance. However, the prior art did not point out that NADPH is (one of) the limiting factor(s).
The BGH ruled that the skilled person "... has an incentive to consider an improvement of that particular factor in the complicated metabolic system only if it is not known or to be expected with a sufficient degree of certainty that this factor is limiting, i.e. not available in a sufficent amount in the known methods" (cited from the headnote).