assimilatory

Assimilatory is an adjective used in biology and biochemistry to describe processes that incorporate inorganic nutrients into organic molecules for biosynthesis. It contrasts with dissimilatory processes, which use the same substrates to obtain energy or to maintain redox balance without building biomass.

Nitrogen assimilation involves uptake of inorganic nitrogen, such as nitrate or ammonium, and reduction to ammonium that is then incorporated into amino acids and nucleotides. In many organisms, nitrate is reduced to nitrite and then to ammonium by assimilatory nitrate and nitrite reductases, followed by incorporation into glutamine and glutamate via the enzyme system glutamine synthetase and glutamate synthase (the GS-GOGAT cycle). Plants, fungi, and many bacteria rely on these pathways to supply amino groups for biosynthesis.

Sulfur assimilation follows a similar pattern. Inorganic sulfate is activated and reduced to sulfide, which is then incorporated into cysteine via the enzymes ATP sulfurylase, APS reductase, sulfite reductase, and cysteine synthase.

Assimilatory pathways are widespread in autotrophs and heterotrophs and are regulated by cellular nitrogen and sulfur status, energy availability, and environmental conditions. They are distinct from dissimilatory pathways that use inorganic substrates for energy production, such as dissimilatory nitrate or sulfate reduction in anaerobic microbes.