Single-turnover of nitric-oxide synthase in the presence of 4-amino-tetrahydrobiopterin: proposed role for tetrahydrobiopterin as a proton donor.

Tetrahydrobiopterin (BH4) is an essential cofactor of nitric-oxide synthase (NOS) that serves as a one-electron donor to the oxyferrous.heme complex. 4-Aminotetrahydrobiopterin (4-amino-BH4) is a potent inhibitor of NO synthesis, although it mimics all allosteric and structural effects of BH4 and exhibits comparable redox properties.

Role of ribonucleotide reductase in regulation of cell cycle progression during and after exposure to moderate hypoxia.

Earlier studies have shown that the retinoblastoma protein (pRb) is involved in cell-cycle regulation under conditions of moderate hypoxia, which is the term we use to denote oxygen concentrations just above the lower level giving full respiration, ie. 1300 ppm O2. We have studied the cell cycle regulatory influence of varying levels of ribonucleotide reductase under moderate hypoxia in human cancer cells with either functional (T47D and T47DHU-res) or non-functional pRb due to expression of HPV18 E7 (HeLa S3).

Stability and transmetallation of the magnetic resonance contrast agent MnDPDP measured by EPR.

MnDPDP [manganese(II) N, N'-dipyridoxylethylenediamine- N, N'-diacetate-5,5'-bis(phosphate)] is the active component of Teslascan, a contrast medium for magnetic resonance imaging of the liver. It has previously been shown that MnDPDP is rapidly dephosphorylated to the monophosphate MnDPMP and the non-phosphorylated MnPLED, and that all these substances are rapidly transmetallated to the corresponding Zn complexes. In the present study we used EPR at 9 and 230 GHz to show that no free Mn(2+) ions can be detected in the product or in a mixture of MnDPDP and human serum.