Direct calculation of the sizes of DNA fragments separated by gel electrophoresis using programmes written for a pocket calculator.

In order to facilitate the direct computation of the sizes of DNA fragments separated by gel electrophoresis, we have written and evaluated programmes for the Hewlett-Packard 41C programmable calculator. The sizes estimated for DNA fragments of known length using some of these programmes were found to be more accurate than the estimates obtained by conventional graphical procedures. These programmes should be adaptable to other programmable calculators.

Human placental aryl hydrocarbon hydroxylase: studies with fluorescence histochemistry.

Tissue sections from human placentas taken at term were studied after time-sequential incubations with benzo[a]pyrene and appropriate cofactors for mixed-function oxidation. Fluorescence microscopy revealed that the enzymic reaction appeared to be most active in the syncytial trophoblast, though the fluorescence of hydroxylated metabolites also could be observed in other placental cell types. A comparison of sections from placentas with very low versus very high aryl hydrocarbon hydroxylase activities provided evidence that induction of the human placental enzyme system with pol7cyclic aromatic hydrocarbons also appeared to occur primarily in the syncytium. When considered in conjunction with previous studies on human placental aryl hydrocarbon hydroxylase, the results tended to indicate that fetal elements of the human placenta contain the necessary electron-transport components for catalysis of mixed-function oxidations of chemical carcinogens and other foreign compounds and that this hydroxtlase system is readily inducible in the same fetal cells by components present in cigarette smoke.