Calcium dependence of the activation and inactivation kinetics of the light-activated phosphodiesterase of retinal rods

The Ca2+ dependence of the kinetics and light sensitivity of light-activated phosphodiesterase was studied with a pH assay in toad and bovine rod disk membranes (RDM), and in a reconstituted system containing GTP-binding protein, phosphodiesterase and rhodopsin kinase. Three statistics, peak hydrolytic velocity, turnoff time, and time to peak velocity, were measured. ATP decreased phosphodiesterase light sensitivity nearly 10-fold and accelerated the dim-flash kinetics of cGMP hydrolysis when compared to those with GTP alone. CA2+ reversed all of the effects of ATP, Ca2+ increased peak velocity, turnoff time, and time to peak velocity, to the values obtained with GTP alone. The Ca2+ dependence of peak velocity and turnoff time can be characterized as hyperbolic saturation functions with a K0.5 for Ca2+ of 1.0-1.5 mM in toad RDM. In bovine RDM the Ca2+ dependence of peak velocity and turnoff time has a K0.5 of 0.1 mM Ca2+. The Ca2+ dependence in the reconstituted system is similar to that in bovine RDM for peak velocity (K0.5 = 0.1 mM Ca2+) but differs for turnoff time (K0.5 = 2.5 mM Ca2+). We tested the hypothesis that a soluble modulator, normally required to confer submicromolar Ca2+ sensitivity, was too dilute in our assay by comparing data obtained at one RDM concentration with those obtained at 10-fold higher RDM, and therefore a constituent protein, concentration. We observe no difference and present a formal analysis of these data that excludes the hypothesis that the soluble modulator binds its target protein with Kd less than 5 microM. The lack of submicromolar Ca2+ dependence of any of the steps in the cGMP cascade that underlie cGMP phosphodiesterase activation and inactivation in vitro argues against Ca2+ regulation of these steps having a significant role in the light adaptation of the intact rod.     

Characterization and localization of the sporulation glucoamylase of Saccharomyces cerevisiae

Glucoamylase (SGA) was purified approximately 250-fold from sporulating Saccharomyces cerevisiae cells. The partially purified enzyme was active against glycogen, starch, maltotriose and maltose. It exhibited maximum catalytic activity against glycogen at pH 5.5. The enzyme appears to be glycosylated, because it bound to lentil-lectin Sepharose. SGA was expressed in vegetatively growing cells under the control of the GAL1 promoter, and the cellular location of the enzymatic activity determined by fractionation techniques. SGA was preferentially recovered in fractions which were enriched for the vacuolar hydrolases, carboxypeptidase Y and alpha-mannosidase.     

Use of the fluorescent antibody technique for the evaluation of Arthroderma uncinatum in soil

The fact that Arthroderma uncinatum can grow through soil has been demonstrated by the fluorescent antibody technique which appears to be a useful tool in investigating the ecology of keratin-decomposing fungi in the soil.     

Trichuris trichiura Infestations in the United Kingdom and Treatment with Difetarsone

Stool specimens were examined for the parasite Trichuris trichiura from 1,860 patients in 17 hospitals for the mentally subnormal in the U.K. It was found in 10 of these hospitals, and an overall incidence of 13·2% was recorded. Most cases occurred in the South, where the overall incidence was 36·3%.Difetarsone was used in the treatment of infestations in two hospitals, and proved to be very well tolerated, cure rates of 81 to 88% being obtained.