Amino acids in sandal (Santalum album L) with special reference to cis-4-hydroxy-l-proline and sym. homospermidine

Abstract

Sandal (Santalum album L) contains several interesting amino acids and amines which are not seen in other plants. This includes cis-4-hydroxy-l-proline in free form in leaves, flowers and seeds while trans-4-hydroxy-l-proline in bound form. Traces of 3, 4 dehydroproline is also detected in sandal leaves. Biosynthesis of cis-4-hydroxy proline indicates that hydroxylation taken place at proline present in peptidyl form especially bound to glutamic acid and aspartic acid. Pyrrolizidine-2-carboxylic acid an interesting isatin positive heterocyclic compound is also present in sandal leaves. Sandal also contains sym. homospermidine which is not present in any other plants till today. Biosynthesis of sym. homospermidine goes by a unique pathway of putrescine oxidation, Schiff base formation, condensation and reduction. Moreover sandal leaves contain γ-glutamyl derivative of the lachrymatory precursor of onion, γ-glutamyl-S-propenyl cysteine superoxide. This review summarizes the studies on the amino acids in sandal.

Recharacterization of the mammalian cytosolic type 2 (R)-β-hydroxybutyrate dehydrogenase as 4-oxo-l-proline reductase (EC 1.1.1.104)

“…These results confirm that BDH2 catalyzes the formation only of cis-4-hydroxy-L-proline, which has been considered a microbial and plant metabolite (8,9) and non-physiological compound in mammalians (10).…”

“…We characterized this enzyme biochemically and showed that it catalyzes the reversible conversion of 4-oxo-L-proline to cis-4hydroxy-L-proline, with distinct substrate specificity and catalytic efficiency. BDH2 is, therefore, the first mammalian enzyme capable of yielding cis-4-hydroxy-L-proline, a metabolite thought to only be of microbial and plant origin (8,9). We also revealed that intact HEK293T cells efficiently metabolize 4-oxo-L-proline to cis-4hydroxy-L-proline.…”

“…Upon hydroxylation of specific proline residues, HIF-1α protein is recognized by the ubiquitin E3 ligase, polyubiquitinated, and directed to the proteasome for proteolysis (7). However, cis-4-hydroxy-L-proline is currently considered absent from mammalian tissues and naturally occurs only J o u r n a l P r e -p r o o f 3 in some species of bacteria, fungi, and plants (8,9,10). Interestingly, cis-4-hydroxy-L-proline was shown to incorporate into collagens, preventing the correct hydroxylation of L-proline residues and the assembly of the triple helix (11).…”

A Specific and Sensitive Enzymatic Assay for the Quantitation of L-Proline

“…Free trans-4-hydroxy-L-proline was found at low levels in oak and pepper plants and its content changed similarly to L-proline in response to stress (Oufir et al, 2009;del Amor et al, 2010;Florencio-Ortiz et al, 2018). Free cis-4-hydroxy-L-proline seems to be a specialty of sandal (Santalum album L) and related species, where it constitutes up to 10% of the dry weight in some tissues (Radhakrishnan and Giri, 1954;Kuttan et al, 2015). Pipecolate is a degradation intermediate of lysine and its content was found to be four times higher than L-proline in Arabidopsis leaves after infection with Pseudomonas syringae pv maculicola (Návarová et al, 2012).…”

Anaerobic Hydroxyproline Degradation Involving C–N Cleavage by a Glycyl Radical Enzyme

“…Cis -4-hydroxy- l -proline (c4L-HP) is also present in nature. It has been found in bacteria such as Sinorhizobium melilotti, in plants such as sandalwood tree (Santalum album), , and is produced by fungi Amanita phalloides as a component of phallotoxin. Hydroxyproline betaines (betonicine and turicine) also function as osmoprotectants in plants .…”