Algae, sulfate assimilation

Alanine residues, glyceraldehyde-3-phos-phate dehydrogenase, 11,12 Alcohols, catalase smd, 388, 398, 401 Aldehydes, glyceraldehyde-3-phosphate dehydrogenase smd, 39 Algae, sulfate assimilation by, 279, 280 Alkali... 

Fig. 40. A proposed unified scheme of sulfate assimilation in algae. Adenylyl sulfate (APS) transfers the sulfo group via APS-sulfotransferase to form Car-S-SOr (Car = carrier), which is reduced further by thio-sulfonate reductase to Car-S-S which yields the thiol group of cysteine. In addition, if sulfite is released from Car-S-SOa (i.e., by thiol or from mutated sites) or if it enters the cell from outside, it can be reduced via a separate sulhte reductase. From Abrams and Schiff (57i).

In the presence of appropriate enzymes, the sulfate group of PAPS can be donated to various acceptors, such as carbohydrates, steroids and phenols, or become reduced to sulfite for assimilatory purposes. Figure 40 shows a unified scheme for sulfate and sulfite assimilation by algae as proposed by Abrams and Schiff 371). 

The most important metabolic reaction is the assimilation of sulfur into organic forms which ultimately require the reduction of oxidized sulfur to the oxidation level of sulfide. This reduction is effected by the majority of microorganisms (bacteria, algae, fungi) and plants and, because of its abundance, sulfate is the dominant precursor of reduced sulfur. Pathways of assimilatory sulfate reduction are discussed briefly in Chapter 6.2 and depicted in Fig. 6.2.1 (p. 317). 

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