Chitin structure and chitinase activity: isolation of structurally intact chitins.

Assessment of chitinase kinetics and mechanism in vitro has been hampered by lack of suitable substrates. We have previously reported rapid linear initial chitinase velocity with chitin substrate isolated from insect larval cuticle. Such chitin is shown to be fibrous in the light microscope. Methods are described for preparing fibrous chitins from any animal source including calcified carapaces. Evidence is given that chitin native fine structure in situ is maintained by structural proteins which in the fibrous chitin isolates are functionally replaced by covalently bound ester groups. Chitin fiber analogues thus reconstructed appear to have retained their native fine structure.

Quantification of Schistosoma mansoni in mouse lungs by radioassay and autoradiography of 75Se-labeled schistosomula.

Lung radioassay and compressed lung autoradiography of 75Se-labeled schistosomula were used to quantify lung schistosomula. Recovery of schistosomula from minced lung tissue after a 4-hr incubation yielded 69.4 +/- 6.3% of the total number present as demonstrated by subsequent autoradiography of these tissues. Radioassay of lung tissue was considered a valid alternative to autoradiography only for parallel comparisons and those not requiring estimation of the actual number of schistosomula. The number of schistosomula in the lungs on day 6 was significantly correlated with radioactivity in the tail on day 1 (r2 = 91.8%). It was concluded that compressed lung autoradiography provides both an alternative to and an adjunct to standard schistosomulum recovery techniques in the assay of early S. mansoni infections.

Naturally occurring insect growth regulators. II. Screening of insect and plant extracts as insect juvenile hormone mimics.

Ethereal extracts prepared from the larvae, pupae, or eggs of 10 species of insects and from various parts of 343 species of higher plants were screened for juvenilizing effects against Tenebrio molitor and Oncopeltus fasciatus. Activity in both species was shown by an extract of the larvae of the stable fly, Stomoxys calcitrans, whereas an extract of the pupae was active in O. fasiatus only. Extracts of two plant species (Echinacea angustifolia roots and Chamaecyparis lawsoniana seeds) showed high juvenilizing activity in T. MOLITOR, AND EXtracts of five plant species (Clethra alnifolia stems, leaves, and fruits, Sassafras albidum roots and root bark, Eucalyptus camaldulensis stems and bark, Pinus rigida twigs and leaves, and Iris douglasiana roots, stems, and fruits) were highly active in O. fasciatus an extract of Tsuga canadensis leaves showed lower activity in this insect. Extracts of 16 species of plants showed high insecticidal activity (mortality) in O. fasciatus but lacked juvenilizing properties in both species of test insects.