Determination of aspartate kinase activity in maize tissues

Aspartate is the common precursor of the essential amino acids lysine, threonine, methionine and isoleucine in higher plants. In addition, aspartate may also be converted to asparagine, in a potentially competing reaction. The latest information on the properties of the enzymes involved in the pathways and the genes that encode them is described. An understanding of the overall regulatory control of the flux through the pathways is undisputedly of great interest, since the nutritive value of all cereal and legume crops is reduced due to low concentrations of at least one of the aspartate-derived amino acids. We have reviewed the recent literature and discussed in this paper possible methods by which the concentrations of the limiting amino acids may be increased in the seeds.

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The aspartic acid metabolic pathway, an exciting and essential pathway in plants

Azevedo

2006

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Lysine and threonine biosynthesis in sorghum seeds: characterisation of aspartate kinase and homoserine dehydrogenase isoenzymes

Ferreira

Meinhardt

Azevedo

2006

Annals of Applied Biology

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Aspartate kinase (AK, EC 2.7.2.4) and homoserine dehydrogenase (HSDH, EC 1.1.1.3) have been partially purified and characterised from immature sorghum seeds. Two peaks of AK activity were eluted by anion‐exchange chromatography [diethylaminoethyl (DEAE)‐Sephacel] with 183 and 262 mM KCl, and both activities were inhibited by lysine. Similarly, two peaks of HSDH activity were eluted with 145 and 183 mM KCl; the enzyme activity in the first peak in elution order was shown to be resistant to threonine inhibition, whereas the second was sensitive to threonine inhibition. However, following gel filtration chromatography (Sephacryl S‐200), one peak of AK activity co‐eluted with HSDH and both activities were sensitive to threonine inhibition, suggesting the presence of a bifunctional threonine‐sensitive AK–HSDH isoenzyme with a molecular mass estimated as 167 kDa. The activities of AK and HSDH were studied in the presence of lysine, threonine, methionine, valine, calcium, ethylene glycol bis(2‐aminoethylether)‐N,N,N′N′‐tetraacetic acid, calmodulin, S‐adenosylmethionine (SAM), S‐2‐aminoethyl‐l‐cysteine (AEC) and increasing concentrations of KCl. AK was shown to be inhibited by threonine and lysine, confirming the existence of two isoenzymes, one sensitive to threonine and the other sensitive to lysine, the latter being predominant in sorghum seeds. Methionine, SAM plus lysine and AEC also inhibited AK activity; however, increasing KCl concentrations and calcium did not produce any significant effect on AK activity, indicating that calcium does not play a role in AK regulation in sorghum seeds. HSDH also exhibited some inhibition by threonine, but the majority of the activity was not inhibited, thus indicating the existence of a threonine‐sensitive isoenzyme and a second predominant threonine‐insensitive isoenzyme. Valine and SAM plus threonine also inhibited HSDH; however, increasing concentrations of KCl and calcium had no inhibitory effect.

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Exploring the role of carbon and nitrogen metabolism in Chenopodium quinoa (Willd.) from the commencement of grain growth until maturity

Grewal

Gill

Chandora

2022

Preprint

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Co-ordination between carbon and nitrogen metabolism plays a vital role in maintaining the source-sink relationship between the reproductive structures (inflorescence and seed). The present investigation was carried out to study carbon and nitrogen metabolism in quinoa genotypes IC411824, IC411825, EC507747 and EC507742 at different stages of anthesis and post -anthesis, which could affect seed growth and maturity. Carbon metabolism enzymes such as acid invertase, sucrose synthase (cleavage), and sucrose phosphate synthase showed increased activity from 75 to 90 days after sowing (DAS) in inflorescence of quinoa genotypes, which might be responsible for the assimilation of carbohydrates required for seed development during the post-anthesis period. Activities of acid invertase and sucrose synthase (cleavage) were observed to be maximum in seeds of quinoa genotypes at 110 DAS, then decreased as seed development progressed, reaching a minimum near seed maturity at 124 DAS. Nitrogen metabolizing enzymes such as glutamate dehydrogenase and nitrite reductase plays a central role in the re- assimilation of amides from the amino group of asparginase at 90 DAS in inflorescence and 124 DAS at seed maturity. IC411825 and EC507747 genotypes had better availability to assimilate the nutrients and their remobilization during the onset of seed development. The pattern of carbon and nitrogen metabolism enzymes at different stages of inflorescence and grain development influenced the source sink relationship mediating partitioning and accumulation of assimilates during of anthesis and post anthesis periods of grain development in quinoa, which eventually led to grain development and yield establishment.

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Determination of aspartate kinase activity in maize tissues

Cited by 3 publications

References 24 publications

The aspartic acid metabolic pathway, an exciting and essential pathway in plants

The aspartic acid metabolic pathway, an exciting and essential pathway in plants

Lysine and threonine biosynthesis in sorghum seeds: characterisation of aspartate kinase and homoserine dehydrogenase isoenzymes

Exploring the role of carbon and nitrogen metabolism in Chenopodium quinoa (Willd.) from the commencement of grain growth until maturity

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