THE RELATIONSHIP BETWEEN CHEMICAL STRUCTURE AND THE RESPONSE OF BLOWFLIES TO TARSAL STIMULATION BY ALIPHATIC ACIDS

Using the technique of proboscis extension in antennectomized-labellectomized flies, the rejection thresholds of Phormia regina for 18 fatty acids and one mineral acid have been determined. The conclusions reached on the basis of these data may be summarized in the following terms: Tarsal stimulation by acids involves the summation of components from at least two sources. Of these the hydrogen ion is the most important. The other major factor is probably the anion rather than the undissociated acid. The stimulating power of the anions (or free acid molecules) increases with increasing chain length in both the mono- and dicarboxylic series, but the rate of increase decreases as the series is ascended. Acids containing 6 or more carbon atoms are not sufficiently soluble in 0.1 M sucrose to reach the threshold of rejection. Substitution of —H in the acyl grouping by —Cl, —OH, =O or —COOH, the presence of a C=C bond, or a shift from the trans- to the cis- configuration all diminish the effectiveness of the anion (or free acid). But since such alterations also augment the degree of dissociation and consequently the concentration of hydrogen ions, the net result is ordinarily a lowering of threshold in terms of the molar concentration required for rejection.

REJECTION THRESHOLDS OF THE BLOWFLY FOR A SERIES OF ALIPHATIC ALCOHOLS

Series of concentrations of 15 aliphatic alcohols were presented in 0.1 M sucrose to the tarsi of antennectomized-labellectomized blowflies (Phormia regina Meigen). With the pri-n-alcohols the mean concentrations at rejection formed a Traube series. When the rejection thresholds for all the alcohols tested were compared with their boiling points, vapor pressures, molecular surface areas) molecular moments, water-cottonseed oil distribution coefficients, standard free energies, and activity coefficients, a very high degree of correlation was found in each case. It is concluded that the limiting process which was measured is concerned with the receptor cells rather than with some other element in the complex response. Stimulative power was evidently not dependent on osmotic pressure nor on rate of molecular diffusion in solution, and the correlation with vapor pressure was inverse. It is judged that surface energy relationships are concerned in stimulation, but the exact mechanism cannot be defined until more is known about the structure of the sensory surface and about the process of excitation. The physiological activity of the alcohols is related more closely to the ease with which they gain access to the cell than to their chemical interaction with cellular constituents.

Peptidase increase accompanying growth of the larval salivary gland of Drosophila melanogaster

1. The larval salivary gland of Drosophila melanogaster offers an opportunity to study growth in a tissue in which no cell division occurs but in which the cells increase in size. 2. Measurements of alanylglycine (AG)-peptidase content have been made in three stocks of Drosophila melanogaster at different growth stages of the larval salivary gland, and have been correlated with its total nitrogen and volume. 3. During the prepupal instar, the AG-peptidase content of the gland increases parallel with total nitrogen but decreases when histolysis of the gland begins. Conversely, a benzoyl-l-arginineamide-hydrolyzing endopeptidase is not measurable until histolysis sets in. 4. In the final larval growth period of a giant mutant, there is a concomitant increase in peptidase, total nitrogen, and volume of the gland. 5. A similar association of peptidase content and total nitrogen is found in comparing glands of different sizes from the giant stock, at the time of maximal peptidase content in the prepupa. 6. The data are interpreted as evidence for an association of AG-peptidase with growth of the cells in the gland. This agrees with the earlier interpretation by Linderstrøm-Lang and Holter of data obtained from study of more complex tissues. 7. A survey of the available measurements of peptidase content in other organisms shows that wherever an increase of cell substance occurs, peptidase content increases. Conversely, peptidase remains constant where cell division is unaccompanied by an increase of cell substances. 8. The joint association of peptidases and pentosenucleic acids with protein synthesis is pointed out. 9. The possiblity is considered that peptidases may be essential parts of a unit in which coupled reactions necessary for protein synthesis occur. The rôle of the peptidases in this system is discussed. They may act either synthetically to form new peptide linkages (problematic), or hydrolytically to mobilize the necessary specific amino acids.

Peptidase activities of extracts of salivary glands of Drosophila melanogaster

1. Peptide-splitting enzymes have been studied in buffered glycerine extracts of larval salivary glands of three stocks of Drosophila melanogaster. 2. The ultraviolet absorption spectrum of the glycerine extracts indicates the presence of a considerable amount of nucleic acid. 3. Alanylglycine (AG), leucylglycine (LG), leucylglycylglycine (LGG), glycylglycine (GG), and diglycylglycine (GGG) are split by the gland extracts in descending order of activity. 4. Of the various metals added, manganese was the only one found to give clear cut activation and that only with LGG as substrate. Cysteine inhibited the splitting of both AG and LG. 5. Comparison of the data with those published indicates the presence in the extracts in descending order of activity (at pH 7.6, 40°C.) of at least four enzymes: an AG-dipeptidase, an LG-dipeptidase, a leucineaminopeptidase, and possibly an aminopolypeptidase. 6. Optimum conditions for the measurement of the enzyme splitting AG were determined. The pH activity and kinetic data are typical for an AG-dipeptidase. 7. An enzyme (probably cathepsin II) splitting benzoyl-l-arginineamide (pH 5.0) with cysteine activation was observed to occur with very low activity in gland extracts.

Methods for following the fate of infectious agents fed to single flies

Methods have been devised which facilitate the handling, feeding, and collection of excreta from individual flies bred in the laboratory. Using these methods, quantitative studies can be carried out in which known amounts of infectious material are fed to flies and the fate of these agents determined. It has been possible to determine the persistence of excretion of viruses, and the amount of the ingested virus recovered in the excreta and in the bodies of the flies as well.

Cell structure and the metabolism of insect flight muscle

The biochemical properties of insect flight muscle were investigated to ascertain the mechanisms whereby energy is made available for the contractile processes. It was found: 1. The endogenous respiration of muscle homogenates was diminished by starving the flies. The substrate for this respiration was probably glycogen. 2. To obtain the maximal rate of oxidation of glucose, the homogenate had to be fortified with inorganic phosphate, Mg ions, ATP, and cytochrome c. The nucleotides, AMP and ADP, were not as effective as ATP. The addition of DPN or TPN was not necessary for this system. 3. Flight muscle homogenates oxidized glycogen, some sugars, and amino acids, as well as the intermediates of the glycolytic and tricarboxylic acid cycles. Other evidence demonstrated the substrate specificity of the muscle. 4. By centrifugation, the muscle homogenate was divided into two fractions: one, a soluble fraction representing the sarcoplasm; the other, the particulate fraction which contained the fibrils and the sarcosomes. 5. The particulate fraction, alone, oxidized all the citric acid cycle intermediates, α-glycerophosphate, phosphopyruvate, and the amino acids, glutamic, proline, and cysteine. Regardless of the substrate, no oxygen uptake was found with the sarcoplasm by itself. 6. A recombination of the sarcoplasm and the particulate component was required for the oxidation of glycogen, the hexoses, and all the phosphorylated intermediates of glycolysis, except phosphopyruvate. 7. Isolated mitochondria accounted for all the enzymatic activity of the particulate fraction. These results demonstrate that the enzymes of intermediate metabolism are localized in the sarcoplasm or sarcosomes. The third cytological entity, the myofibrils, plays no role in the energy-providing scheme. From a functional viewpoint, the sarcoplasm and the mitochondria, in combination, furnish the energy for the actomyosin contraction. The results are discussed in relation to analogous findings in other insects and vertebrates.

Functional significance of the crystal cells in the larva of Drosophila melanogaster

Cytoplasmic crystalline inclusions are found in some larval haemocytes of Drosophila melanogaster. Blackening can be experimentally induced in these cells, and previously it was suggested that either the substrate or enzyme for the tyrosine-tyrosinase system leading to melanin production in Drosophila larvae is found in these inclusions in the crystal cells. The present report is an attempt to further localize the enzyme and substrate. Larvae have been fed on food containing α-C¹⁴-tyrosine and autoradiographs of the blood cells taken from these larvae subsequently prepared. The C¹⁴ activity in the crystal cells is restricted to the crystal inclusions in the cells and is significantly higher than that found in the other type of haemocytes, the plasmatocytes. When samples of the blood cells are incubated in DOPA solution, the extra-crystalline cytoplasm becomes blackened while the crystals themselves remain colorless. These observations are consistent with the hypothesis that the substrate is localized in the crystal inclusions whereas enzyme is found in the surrounding cytoplasm. An in vivo structural isolation would serve to separate enzyme and substrate rather than an inhibition by dehydrogenases as postulated by previous authors. In vitro examination with the phase microscope has shown that the crystal cells rupture easily and the crystals dissolve in the haemolymph. Therefore any treatment which tends to disrupt the structural integrity of the cell will allow the enzyme and substrate to come together. Humoral factors preceding metamorphosis might account for the in vivo release of the enzymatic reaction by initially altering the permeability of the cell.