Saccharopine

The first step in the biological degradation of lysine is reductive animation with a-ketoglutarate to give saccharopine. Nicotinamide adenine dinucleotide phosphate (NADPH), a relative of NADH, is the reducing agent. Show the mechanism. 

Fujimori, T., R. Kasuga, H. Kaneko, and M. Noguchi. Isolation of solaveti-vone from Nicotiana tabacum. Phytochemistry 1977 16 392. Kawashima, N., N. Inoue, and M. Noma. Saccharopine from tobacco leaves. Phytochemistry 1978 17 991A. Itoh, T., T. Ishii, T. Tamura, and T. Matsumoto. Four new and other 4-al-pha-methylserols in the seeds of Solanaceae. Phytochemistry 1978 17 971-977. 

He isoleucine, Kyn kynurenine, Leu leucine, Lys lysine, Met methionine, MTHFR 5,10-methylene tetrahydrofolate reductase, Orn ornithine, p plasma, P5C pyrroline-5-carboxylic acid, PEA phosphoethanolamine, Phe phenylalanine, P-Hyl O-phosphohydroxylysine, Pip pipecolic acid, Pro proline, Sacch saccharopine, Sar sarcosine, Ser serine,... 

The essential amino acid lysine (2,5-diaminohexanoic acid) can be degraded via two pathways, viz. the so-called saccharopine pathway and the pipecolic acid (PA) pathway. Both pathways merge at the level of a-aminoadipic acid semialdehyde (AASA). It is generally accepted that the saccharopine pathway constitutes the major breakdown pathway. However, the PA pathway has attracted much attention since the discovery of the association between the presence of elevated PA levels and Zellweger syndrome almost 40 years ago. Mainly because the analysis of amino acids was the primary biochemical approach for studying presumed inborn errors of metabolism, PA in Zellweger syndrome was discovered even before it was realized that this disorder was based on a defect of peroxisomal functions. 

The hyperlysinemias are characterized by a block in the saccharopine pathway. Subsequently, the PA pathway is overloaded. It is assumed that the capacity of the latter pathway is not sufficient to tackle all lysine molecules. 

This is followed by ATP-dependent reduction to the aldehyde.2643 The final step of transamination is not accomplished in the usual way (with a PLP-dependent enzyme), but through formation of a Schiff base with glutamate and reduction to saccharopine.265 Oxidation now produces the Schiff base of lysine with 2-oxoglutarate. 

Fig. 24. Four out of five amino acid residues around the reactive cysteine are identical in yeast saccharopine dehydrogenase and sheep sorbitol dehydrogenase.

Ketoglutarate reductase catalyzes the formation of saccharopine from lysine, which is the first step in a major pathway for lysine catabolism. NADPH and a-ketoglutarate are cofactors in the reaction. 

The o-phthaldialdehyde derivatives of lysine and saccharopine were separated on a Ultrasphere-XL ODS column (4.6 mm x 70 mm, 3 /an). The column was equilibrated using methanol-0.1 Af sodium acetate (pH 6.7) in a 16 84 ratio. The flow rate was 1.6 mL/min. After injection, methanol was increased linearly to 20% in 0.5 minute. A further increase to 20% methanol occurred at 11.5-12 minutes. A return to 16% methanol occurred between 19 and 19.5 minutes, and the column was equilibrated for 8.5 minutes prior to... 

A simple assay based on potent and specific inhibition of jack bean a-mannosidase has been devised for determining low concentrations of 162 (up to 0.5 cm ) in M anisopliae cultures (110). The new assay was used to demonstrate that the addition of L-lysine (163) to the culture medium stimulated production of the alkaloid by approximately fourfold. Other early metabolic precursors of 162 in this fungus, including a-aminoadipic acid, saccharopine (164), L-pipecolic acid (165), and L-lysine itself, were quantified by reverse-phase HPLC analysis of mycelial extracts derivatised with 9-fluorenylmethyl chloroformate (FMOC) (111). 

L-Saccharopine. N-(5-Amino-5-carboxypemyt)-L-glutamic acid -Af-(L-glutar-2-yl)-L-lysine. CnH NjO. mol wt 276.29. C 47.82%. H 7.30%, N 10.14%, O 34.75%. A lysine precursor in the aminoadipic add-lysine pathway in yeast Darling. Larsen, Acta Chem. Scand. IS, 743 (1961) Kjaer. Larsen, ibid. 750 Kuo et al. Biochem Biophys. Res. Commun. 8, 227 (1962) Trupin, Broquist, J. Biol Chem. 240, 2524 (1965) Jones, Broquist, ibid. 241, 3430 sqq. (1966). Isoln from mycelium of the yeast Candida utilis Marimoto, Yamano, Biochem. Z. 340, 155 (1964). 

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