Ascorbic acid 2-phosphates, enzymatic

A similar study has also been conducted to determine the suitability of ascorbic acid 2-phosphate (AAP) as an alternative substrate to 4-AP for AP under identical conditions [48], Although 4-APP and AAP were suitable substrates for amperometric immunosensors, 4-APP was superior owing to its sixfold faster enzymatic reaction and lower detection potential (approximately 200-400mV). Notably, the lower detection potential for the hydrolysis product of 4-APP minimizes interferences from other species and hence improves the sensitivity of the immunosensor. 

Two different protein phosphatases were used the one from Upstate Biotechnology (New York, USA), from human red blood cells, and the one from GTP Technology (Toulouse, France), isolated from SF9 insect cells infected by baculovirus. The enzymatic activity of these two enzymes towards several substrates was investigated by cyclic voltammetry and steady-state chronoamperometry (see experimental details in Refs. [86,87]). First, commercial substrates were tested. Ascorbic acid 2-phosphate and phenyl phosphate were not recognised by the protein... 

P 75] A static enzyme assay experiment was carried out using a stopped-flow method [161]. This is commonly used for monitoring reaction kinetics. P-Galacto-sidase was used as model enzyme to convert the substrate fluorescein mono-p-D-galactopyranoside (FMG) via hydrolysis into fluorescein. As buffer solution 10 mM potassium phosphate at pH 7.2 with 1 mM ascorbic acid was used to minimize photobleaching. The enzymatic reaction is accompanied by a change in fluorescence intensity which can be monitored with a microscope. 

Udenfriend suggested a simple non-enzymatic system as a possible model of monooxygenase [44]. It involves an iron(II) complex with EDTA and ascorbic acid and is capable of hydroxylating aromatic compounds. Later, Hamilton found that this system was able to hydroxylate cyclohexane (however, with very low yield) and epoxidize cyclohexene [45]. Afterwards, a number of similar systems were proposed. For example, Ullrich found two models which are more effective than the Udenfriend system. One of them includes a Sn(II) phosphate complex... 

We studied the enzymatic oxidation of tyrosine using the decapeptide with the consensus sequence as the substrate. Since catechol oxidase from sea mussels is not available, we instead used mushroom tyrosinase for our studies. The oxidations were carried out in a phosphate buffer at ambient temperatures. The reactions were followed using UV spectroscopy and products were separated by HPLC and identified by FAB/MS. The oxidations were also followed in an NMR tube using D2O as the solvent. When the decapeptide Glue-2 (see Table 1) with the consensus sequence was oxidized in the presence of ascorbic acid, mono-dopa was the predominant product. The enzyme selectively oxidized the tyrosine at position 9.20 Glue-7, in... 

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