Biochemistry of sulphur reduction

Sulphur | its biochemistry || how the reduction of Sulphur occurs ||||
plants and other microorganisms

1. SHRI SHIVAJI ARTS, COMMERCE AND SCIENCE COLLEGE, AKOLA DEPARTMENT OF MICROBIOLOGY GUIDED BY: DR. MONIKA THAKARE MAM Presented By: Shraddha M. Madghe M.Sc. First Year

2. CONTENT INTRODUCTION BIOCHEMISTRY OF SULPHUR REDUCTION SIMILARITIES BETWEEN ASSIMILATORY AND DISSIMILATORY SULPHATE REDUCTION DIFFERENCES BETWEEN ASSIMILATORY AND DISSIMILATORY SULPHATE REDUCTION ASSIMILATORY SULPHUR REDUCTION DISSIMILATORY SULPHUR REDUCTION

3. Introduction Sulphur is most abundant and widely distributed element in the nature and found both in free as well as combined state. Sulfur occurs in all living matter as a component of certain amino acids. It is abundant in the soil , in proteins and through a series of microbial transformations, ends up as sulfates usable by plants. Sulphur enters in soil in the form of plants and animals residue. It is also added as chemical fertilizer in the form of ammonium sulphate. Sulphur is taken by plants in most oxidized state i.e. Due to this, it is added in the soil in the form of ammonium sulphate which supply both nitrogen as well as sulphur.  

4. This involves two types: 1. Assimilatory Sulphur Reduction 2. Dissimilatory Sulphur Reduction Biochemistry Of Sulphur Reduction

5. Similarities Between Assimilatory and Dissimilatory Sulphate Reduction Both processes take place under anaerobic conditions. Also, the starting compound of both processes is sulphate. Furthermore, sulphate acts as the final electron acceptor in both processes. Moreover, both reduction processes are ATP dependent. In addition, the activation of sulphate to adenosine 5’ – phosphosulphate is common to both processes. Besides, they are enzyme-catalyzed reactions. Both reduction processes are carried out by prokaryotes, fungi and photosynthetic organisms.

6. Difference Between Assimilatory and Dissimilatory Sulphate Reduction

7. Assimilatory Sulphur Reduction largely restricted to plants and microorganisms where it provides reduced Sulphur for the formation of amino acids , proteins, nucleic acids, and various Sulphur-containing coenzymes, begins with the activation of sulphate through reaction with ATP to form adenosine 5'-phosphosulphate (APS) and adenosine 3'-phosphate 5'-phosphosulphate (PAPS). Adenosine 5'-phosphosulphate [APS] which is formed during reaction with ATP. Adenosine 3'-phosphate 5'-phosphosulphate (PAPS) which is formed by further phosphorylation of APS at 3’ position PAPS acts on high energy sulphate donor in many esterification reactions and it is usually the substrate participating in sulphate reduction. Assimilatory Sulphur Reduction

8. APS acts as high energy sulphate donor for many esterification reaction and it is usually participating in assimilatory sulphate reduction. Assimilatory sulphate reduction involves NADPH linked 2 electrons. PAPS reduced to give sulphite and 3-phosphoadenosine monophosphate followed by NADPH linked with reduction of sulphite to sulphide catalysed by sulphide reductase . Sulphide is incorporated into biomass which by condensation with serine generating system. Thus, the various transfer reactions of the assimilation sulphate reduction can be summarized as follows:

9. 1.Activation of Sulphate with ATP Organic sulphate reacts with ATP in the presence of enzyme sulfurylase to form adenosine 5'-phosphosulphate (APS) and pyrophosphate [ PPi ].

10. 2. Phosphorylation of APS PAPS APS kinase   APS ATP + ADP Adenosine 5'-phosphosulphate (APS) reacts with Adenosine triphosphate (ATP) to form 3’-phosphoadenosine 5’-phosphosulphate(PAPS) and ADP.

11. 3.Reduction of sulphate The active sulfate of PAPS is subsequently reduced sulfite and adenosine-3,5-diphosphate in presence of PAPS Reductase . This involves transfer of electron from NADH/NADPH to PAPS. PAPS       ADP PAPS Reductase NADH+  

12. 4. Reduction of Sulphite NADPH further reduces sulphite to sulphide i.e. immediately incorporated as amino acid 3 3   +   NADPH NAD S   S   NADPH NAD +   + 6 + 6  

13. 5. The sulphide is immediately used in the formation of cysteine with serine under the catalytic action of enzyme Serine Sulfyhydrase Serine sulfyhydrase Serine Hydrogen Sulphide Cysteine Water

14. Certain organism utilizes sulphate as terminal electron acceptor in anaerobic respiration with production of which is released to environment. Anaerobic bacteria carry out dissimilarity sulphate reduction. The responsible organism are Desulfovibrio vulgaris, Desulfometaculum , etc. When an obligatory anaerobic bacteria carry out dissimilatory Sulphur reduction they are refers to as sulphate reducers. In addition to anaerobic sulphate reducing bacteria , some species of bacillus, pseudomonas and saccharomyces are also found to liberate from but do not plays a major role in dissimilatory sulphate reduction. The most common electron donors are pyruvate, lactate and molecular hydrogen. The reduction of sulphate results in production of Hydrogen Sulphide   Dissimilatory Sulphate Reduction      

15. Mechanism Of Sulphate Reaction Dissimilatory sulfate reduction  is a form of  anaerobic respiration  that uses  sulfate  as the terminal  electron acceptor  to produce  hydrogen sulfide . The mechanism of assimilatory sulphur reduction[ASR] is similar to that of dissimilatory sulphur reduction[DSR]. As activated sulphur participates in this process and APS reduction, Sulphide reduction, Thiosulphate reduction are probably involved in cycle. The reduction of sulphate regenerated ,thiosulphate i ,.e. composite molecules containing sulphur atoms of different valences and . Although , reduction differ in mechanism in assimilatory and dissimilatory process. Sulphide reductase is the similar enzyme present in ASR and DSR. In DSR process specific cytochrome donate electron at various reductase stage rather than NADPH and ATP is generated by this electron transfer reduction. The exact mechanism is not completely understood.  

16. REFERENCES 1. https://www.researchgate.net/figure/Prokaryotic-assimilatory-and-dissimilatory-pathways-of-sulfate-reduction-adapted-from_fig1_342434176 2. https://www.differencebetween.com/difference-between-assimilatory-and-dissimilatory-sulphate-reduction/ 3. https://en.wikipedia.org/wiki/Dissimilatory_sulfate_reduction 4. https://pubmed.ncbi.nlm.nih.gov/398767/ 5. https://www.sciencedirect.com/topics/chemistry/sulfur-cycle 6. https://www.britannica.com/science/sulfur-cycle

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