We have adapted a rapid and sensitive high-pressure liquid chromatographic technique (HPLC) to measure plasma levels of 8-methoxypsoralen (8-MOP) in 22 psoriatic patients receiving photochemotherapy with 8-MOP and long-wave ultraviolet light (PUVA). In this procedure, 1 ml plasma samples containing ammidin as an internal standard are extracted with benzene. After evaporation under nitrogen the residue is redissolved in methylenechloride:acetonitrile, 95:5, and chromatographed using a normal phase HPLC system with a 10 mu silica particle column and a UV detector at 254 nm. The sensitivity of the method is 10 ng/ml plasma. Plasma concentrations of 8-MOP were measured between 2 and 4 hr after ingestion of therapeutic doses of 8-MOP provided by 2 manufacturers. Mean 8-MOP plasma levels were 27 +/- 35 ng/ml plasma 2 hr after ingestion of the only drug presently available on the U.S. market, 8-MOP (Elder). These values were significantly below (p less than 0.001) those obtained with 8-MOP (Roche) which were 104 +/- 79 ng/ml plasma. A number of patients on 8-MOP (Elder) did not have detectable levels of 8-MOP 2 hr after ingestion. The time course patterns also differed, possibly indicating a slower and less complete absorption for 8-MOP (Elder). Repeated time course studies in the same patient were reproducible although the absolute concentrations showed some variation. Preliminary evidence indicates that the plasma levels of 8-MOP have therapeutic relevance.

The ribonucleic acid dependent deoxyribonucleic acid polymerase from avian myeloblastosis virus was shown to synthesize poly(dT) transcripts by a processive mechanism using poly(rA)1100.oligo(dT)12-18 as template and primer. Template challenge experiments demonstrate that at low temperature and ionic strength, the polymerase remains bound to the completed template-daughter strand complex after completion of daughter strand elongation. Higher temperatures and ionic strength increase the dissociation of the enzyme from the complex, thus reducing transcript length. Analysis of product size and quantity indicates that the degree of processivity is also influenced by the types and concentrations of metal ions present and indicates that the metal ions affect the activity of the poly(rA) as a template more than they affect processivity or enzyme activity. The results also lead to the conclusion that initiation is the rate-limiting step under all of our experimental conditions. The arguments for a processive as opposed to distributive mechanism are based on an analysis of enzyme-template interactions, product size, and amount of product made under specific reaction conditions.

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