S 2 hydroxybutyric acid

PBS 11 mM, pH 7.4 with
137 mM NaCl and 3 mM KCl was used as the standard buffer for all experiments
unless stated otherwise. Britton–Robinson universal buffer
(BRB) contains 40 mM phosphoric, boric, and acetic acid. Cultivation
of bacteria was routinely done in the Luria-Bertani (LB) medium (10
g/L peptone from casein, 5 g/L yeast extract, and 10 g/L NaCl) with
100 mg/L ampicillin. In the case of cultivating bacteria carrying
the pNIC-CH plasmid for PaLCTO, ampicillin was replaced
with 50 mg/L kanamycin. General medium components were purchased from
Carl Roth; sodium L-lactate, ferrocenium hexafluorophosphate (FcPF₆), isopropyl β-D-1-thiogalactopytanoside (IPTG), 2,6-dichlorophenol-indophenol
sodium salt hydrate (DCIP), horseradish peroxidase, sodium glycolate,
1,4-BQ, R-2-hydroxybutyric acid, and S-2-hydroxybutyric acid from
Sigma-Aldrich (Germany); S-2-hydroxyvaleric acid from BLD Pharmatech
Ltd. (Shanghai); 2-hydroxypalmitic acid and 2-hydroxy-n-octanoic acid from TCI (Japan); (S)-2-hydroxybutyric
acid and S-(+)-mandelic acid from Fluorochem Ltd. (United Kingdom);
and 10-acetyl-3,7-dihydroxyphenoxazine (AmplexRed) from Chemodex (Switzerland).

(S)-2-hydroxybutyric acid (>97 %, CAS 3347-90-8), sodium (S)-lactate (>98 %, CAS 867-56-1), human plasma (pool, lyophilized, citrate anticoagulant), human serum (male, sterile filtered), and phosphate buffered saline tablets were purchased from Sigma. The latter were dissolved in 200 mL reverse osmosis-generated water with the pH adjusted to 7.40 with NaOH/phosphoric acid. (RS)-2-hydroxybutyric acid sodium salt (>97 %, racemic, CAS 5094-24-6) was from Thermo Fisher Scientific, 2-hydroxybutanoic-d3 acid sodium salt (isotope labeled, racemic, CAS 1219798-97-6) was from Toronto Research chemicals. Sterile human serum and human plasma in sodium citrate, sodium EDTA, and in lithium heparin were obtained from Biotrend CliniSciences Group and were from healthy donors, sterile pooled and gender balanced.
Materials used for liquid chromatography-MS/MS were Elo-Mel isotonic infusion solution from Fresenius Kabi, Graz, Austria, and human serum albumin (200 g/L infusion solution) from Kedrion Biopharma, Austria. Formic acid 99–100 %, AnalaR NORMAPUR®, methanol ≥99,8 %, and HiPerSolv CHROMANORM® were from VWR (Pennsylvania, USA). Purified water was prepared using the Milli Q® Academic water purification System from Millipore GmbH, Vienna, Austria.