Testicular metamorphosis rates in European Starlings maintained under short daily photophases

Juvenile male European Starlings(Sturnus vulgaris) were maintained under discrete fixed daily photophases ranging from 1 to 11 h in duration. Treatment began on 20 December when all birds were reproductively quiescent, and continued until 14 June of the following year.In situ measurements of left testis widths at monthly intervals documented testicular width increases to levels associated with complete spermatogenesis in birds under all photoperiod regimens. Starlings maintained under the shortest and longest photoperiods required fewer days of treatment to achieve spermatogenic testes than did those under intermediate-length photoperiods. Data are consistent with the hypothesis that prolonged daily periods of darkness result in oscillations of a circadian timing system stimulating increased gonadotropin secretion and consequent testicular metamorphosis.     

The preparation and kinetics of lactate dehydrogenase attached to water-insoluble particles and sheets

1. The preparation of lactate dehydrogenase covalently attached to anion-exchange cellulose particles and sheets by use of a dichloro-sym-triazinyl dyestuff, Procion brilliant orange MGS, is described. 2. The stability and kinetic properties of these preparations were investigated. 3. An equation is derived to describe the change in concentration of a substrate when passed through a uniform bed of a substrate-inhibited enzyme. A number of theoretical curves are shown to illustrate the system. 4. A titrimetric assay for lactate dehydrogenase is described, and shown to be stoicheiometric over the range pH5.0-9.2. 5. The results are discussed in relation to previous work, and the effects of charged groups on the support, and of the diffusion film surrounding any particle in suspension, are treated qualitatively.     

Nucleotide pyrophosphatase of rat liver. A comparative study on the enzymes solubilized and purified from plasma membrane and endoplasmic reticulum.

Studies on the subcellular distribution of rat liver nucleotide pyrophosphatase activity revealed its presence in the plasma membrane and the endoplasmic reticulum only. The enzymes from either source were solubilized specifically with trypsin without an apparent change of their catalytic properties. A 200-fold and 1600-fold purification, respectively, was achieved by a procedure including DEAE-cellulose and affinity-chromatography with AMP as ligand, gel filtration on Sephadex G-200 and gel electrophoresis. Both nucleotide pyrophosphatases were isolated as electrophoretically homogeneous soluble proteins. They were shown to contain carbohydrate moieties. The electrophoretic mobility of both enzymes in polyacrylamide gels was identical at three pH values. Dodecylsulfate gel electrophoresis indicated a molecular weight of 137 000 for both glycoproteins. The enzymes hydrolyze a variety of purine and pyrimidine nucleotides yielding a 5'-nucleoside monophosphate. Adenosine 3':5'-monophosphate, nucleic acids and phosphate monoesters are not cleaved, but p-nitrophenyl-thymidine5'-monophosphate is readily hydrolyzed. In view of their substrate and inhibitor specificities the enzymes are considered nucleotide pyrophosphatases rather than phosphodiesterases.