PROTEIN AND NUCLEIC ACID CHANGES DURING GROWTH AND AGING IN THE MOSQUITO

1. Mosquito samples from the entire life span including senescence were analysed for weight, protein, RNA and DNA. 2. The results for each component indicate that maximal values are attained during larval development. No changes were observed during metamorphosis or the adult period. 3. The peak concentration of RNA and DNA was reached on the third day larval age. Protein content and weight were highest on the sixth day. 4. Except for the first 2 days of larval life the DNA/protein ratio was constant. Hence protein content is an index of cell number for this organism. 5. The distribution of the different biochemical components was determined in different body regions and in subcellular fractions. A high concentration of DNA was found in the soluble fraction of larval but not adult homogenates.

FURTHER INVESTIGATIONS OF THE INCORPORATION OF (1-14C)ACETATE INTO THE LIPIDS OF THE SILKWORM BOMBYX MORI L

1. After the injection of sodium [1-(14)C]acetate, the highest incorporation of (14)C into the lipids of the silkworm was observed after 24hr. 2. The specific radioactivity of the palmitic acid fraction was greater and increased more rapidly than that of the stearic acid fraction, which was consistent with the precursor-product relationship to be expected on the basis of current concepts of fatty acid synthesis in vivo. 3. The results indicate the probability of synthesis of lipid components in tissues other than the fat body. 4. Fractionation studies indicate considerable differences in the rate of incorporation of [1-(14)C]acetate into neutral lipids and phospholipids between larvae and pupae as well as among tissues of larvae. 5. The rate of incorporation of [1-(14)C]acetate remains constant throughout pupal development.

TRANSEPIDERMAL POTENTIAL DIFFERENCE: DEVELOPMENT IN ANURAN LARVAE

Skin from bullfrog tadpoles does not show the potential difference characteristic of adult frog skin until several days after the emergence of the forelimbs, presumably because the mechanism for active sodium transport is absent or nonfunctional. Exposure to low concentrations of thyroxine accelerates appearance of the transepidermal potential difference at rates which are related to the dosage. This system may provide a new basis for evaluating the importance of specific biochemical mechanisms in active sodium transport.

TOTAL GLYCOGEN IN THE PEA APHID, ACYRTHOSIPHON PISUM (HARR.) (HOMOPTERA, APHIDIDAE)

In the pea aphid, Acyrthosiphon pisum (Harr.), the amount of glycogen increases steadily as the aphid grows from larval to adult stage. The newly born larva, however, lacks the glycogen reserve.