Fig. 2.

The early response of the cellular innate immune system inhibits NAD⁺‐dependent activity of GAPDH. In response to interferons, viruses or bacteria, the cells express metalloenzymes RSAD2 (viperin) and/or nitric oxide synthase (NOS). RSAD2 uses S‐adenosylmethionine (SAM) to catalyse transformation of CTP to ddhCTP, which inhibit activity of GAPDH. 5´‐deoxyadenosine (5´‐dA) is formed as a by‐product. On the other hand, NOS generates NO, which induces S‐nitrosylation of GAPDH and inhibits its activity.