Guanidino acid hydrolysis by the human enzyme annotated as agmatinase.

Guanidino acids such as taurocyamine, guanidinobutyrate, guanidinopropionate, and guanidinoacetate have been detected in humans. However, except for guanidionacetate, which is a precursor of creatine, their metabolism and potential functions remain poorly understood. Agmatine has received considerable attention as a potential neurotransmitter and the human enzyme so far annotated as agmatinase (AGMAT) has been proposed as an important modulator of agmatine levels. However, conclusive evidence for the assigned enzymatic activity is lacking. Here we show that AGMAT hydrolyzed a range of linear guanidino acids but was virtually inactive with agmatine. Structural modelling and direct biochemical assays indicated that two naturally occurring variants differ in their substrate preferences. A negatively charged group in the substrate at the end opposing the guanidine moiety was essential for efficient catalysis, explaining why agmatine was not hydrolyzed. We suggest to rename AGMAT as guanidino acid hydrolase (GDAH). Additionally, we demonstrate that the GDAH substrates taurocyamine, guanidinobutyrate and guanidinopropionate were produced by human glycine amidinotransferase (GATM). The presented findings show for the first time an enzymatic activity for GDAH/AGMAT. Since agmatine has frequently been proposed as an endogenous neurotransmitter, the current findings clarify important aspects of the metabolism of agmatine and guanidino acid derivatives in humans.

Canavanine utilization via homoserine and hydroxyguanidine by a PLP-dependent γ-lyase in Pseudomonadaceae and Rhizobiales.

Canavanine, the δ-oxa-analogue of arginine, is produced as one of the main nitrogen storage compounds in legume seeds and has repellent properties. Its toxicity originates from incorporation into proteins as well as arginase-mediated hydrolysis to canaline that forms stable oximes with carbonyls. So far no pathway or enzyme has been identified acting specifically on canavanine. Here we report the characterization of a novel PLP-dependent enzyme, canavanine-γ-lyase, that catalyzes the elimination of hydroxyguanidine from canavanine to subsequently yield homoserine. Homoserine-dehydrogenase, aspartate-semialdehyde-dehydrogenase and ammonium-aspartate-lyase activities are also induced for facilitating canavanine utilization. We demonstrate that this novel pathway is found in certain Pseudomonas species and the Rhizobiales symbionts of legumes. The findings broaden the diverse reactions that the versatile class of PLP-dependent enzymes is able to catalyze. Since canavanine utilization is found prominently in root-associated bacteria, it could have important implications for the establishment and maintenance of the legume rhizosphere.

Boron-based donor-spiro-acceptor compounds exhibiting thermally activated delayed fluorescence (TADF).

Four boron-based donor-spiro-acceptor compounds, composed of different donor moieties and borylated 2-phenylpyridines as the acceptor, were studied. Their intense photoluminescence in the solid state can be tuned by changing the donor and long emission lifetimes on the microsecond scale indicate thermally activated delayed fluorescence (TADF).

Synthesis, Structures, and Photophysical Properties of a Series of Rare Near-IR Emitting Copper(I) Complexes.

Herein, we report on the synthesis and structural characterization of a series of trigonal and tetrahedral cationic copper(I) complexes, bearing phosphine or N-heterocyclic carbene ligands as donors, with benzthiazol-2-pyridine (pybt) and benzthiazol-2-quinoline (qybt) acting as π-chromophores. The compounds are highly colored due to their 1MLCT (MLCT = metal-to-ligand charge transfer) states absorbing between ca. λabs = 400-500 nm, with 1ILCT (ILCT = intraligand charge transfer) states in the UV region. The relative shifts of the S0→S1 absorption correlate with the computed highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, the qybt complexes generally being lower in energy than the pybt ones due to the larger conjugation of the quinoline-based ligand. The compounds exhibit, for CuI complexes, rare intense long-lived near-IR emission with λmax ranging from 593 to 757 nm, quantum yields of up to Φ = 0.11, and lifetimes τ of several microseconds in the solid state as well as in poly(methyl methacrylate) films. Although a bathochromic shift of the emission is observed with λmax ranging from 639 to 812 nm and the lifetimes are greatly increased at 77 K, no clear indication for thermally activated delayed fluorescence was found, leaving us to assign the emission to originate from a 3(Cu→pybt/qybt)MLCT state. The red to near-IR emission is a result of incorporation of the sulfur into the chromophore ligand, as related nitrogen analogues emit in the green to orange region of the electromagnetic spectrum. The photophysical results and conclusions have further been corroborated with density functional theory (DFT)/time-dependent DFT calculations, confirming the nature of the excited states and also the trends of the redox potentials.