Synthesis of poly(ethylene glycol)‐bound NADP by selective modification at the 6‐amino group of NADP

The N‐1 position of the adenine ring of NADP was selectively aklylated by the reaction of 2′,3′‐cyclic NADP with 3‐propiolactone to yield 2′,3′‐cyclic 1‐(2‐carboxyethyl)‐NADP (I). Derivative I was converted to a mixture of the isomers of N 6 ‐(2‐carboxyethyl)‐NADP with their phosphate groups at the 2′ or 3′ position (IIa and IIb) by chemical reduction, alkaline rearrangement and chemical reoxidation. Carbodiimide coupling of the mixture of IIa and IIb to α,ω‐diaminopoly(ethylene glycol) gave the 2′,3′‐cyclic derivative of poly(ethylene glycol)‐bound NADP (III), which was enzymically hydrolyzed to yield poly(ethylene glycol)‐bound NADP (PEG‐NADP). PEG‐NADP has good cofactor activity (16–100% of that of NADP) for NADP‐specific and NAD(P)‐specific dehydrogenases except isocitrate and glucose dehydrogenases. For NA d ‐specific enzymes. PEG‐NADP has higher cofactor activity than NADP: for horse liver alcohol dehydrogenase, the cofactor activity of PEG‐NADP is 40 times that of NADP and 14% of that of NAD. Kinetic studies show that for most of enzymes tested, K m values for PEG‐NADP are larger than those for NADP and V values for PEG‐NADP are similar to those for NADP. PEG‐NADP proved to be applicable in a continuous enzyme reactor, in which reactions of glutamate dehydrogenase and glucos‐6‐phosphate dehydrogenase were coupled by the recycling of PEG‐NADP.