Lectin-binding sites on the plasma membranes of rabbit spermatozoa: Changes in surface receptors during epididymal maturation and after ejaculation

Modifications in rabbit sperm plasma membranes during epididymal passage and after ejaculation were investigated by used of three lectins: concanavalin A (Con A); Ricinus communis I (RCA(I)); and wheat germ agglutinin (WGA). During sperm passage from caput to cauda epididymis, agglutination by WGA drastically decreased, and agglutination by RCA(I) slightly decreased, although agglutination by Con A remained approximately unchanged. After ejaculation, spermatozoa were agglutinated to a similar degree or slightly less by Con A, WGA, and RCA(I), compared to cauda epididymal spermatozoa. Ultrastructural examination of sperm lectin-binding sites with ferritin- lectin conjugates revealed differences in the densities of lectin receptors in various sperm regions, and changes in the same regions during epididymal passage and after ejaculation. Ferritin-RCA(I) showed abrupt changes in lectin site densities between acrosomal and postacrosomal regions of sperm heads. The relative amounts of ferritin-RCA(I) bound to heads of caput epididymal or ejaculated spermatozoa. Tail regions were labeled by ferritin RCA(I) almost equally on caput and cauda epididymal spermatozoa, but the middle-piece region of ejaculated spermatozoa was slightly more densely labeled than the principal-piece region, and these two regions on ejaculated spermatozoa were labeled less than on caput and cuada epididymal spermatozoa. Ferritin-WGA densely labeled the acrosomal region of caput epididymal spermatozoa, although labeling of cauda epidiymal spermatozoa was relatively sparse except in the apical area of the acrosomal region. Ejaculated spermatozoa bound only a few molecules of ferritin-WGA, even at the highest conjugate concentrations used. Caput epididymal, but not cauda epididymal or ejaculated spermatozoa, bound ferritin-WGA in the tail regions. Dramatic differences in labeling densities during epididymal passage and after ejaculation were not found with ferritin-Con A.     

The peracid cleavage of 5-methyltetrahydrofolic acid at the C9-N10 bridge.

5-Methyltetrahydrofolate cannot be cleaved at the C⁹N¹⁰ bond by the zinc/HCl reductive or the permanganate oxidative cleavage methods. A new method has been developed to perform this cleavage, using peracetic acid in 50% trifluoroacetic acid; the cleavage is quantitative and nondestructive of γ-glutamyl peptide bonds.     

Studies on the transport mechanism of 5-methyltetrahydrofolic acid in freshly isolated hepatocytes: effect of ethanol.

The effect of ethanol on the transport of 5-methyltetrahydrofolate in freshly isolated hepatocytes in vitro resulted in about a 30% increase in accumulation of substrate. It was shown that this was not due to differences in metabolism, nor to an inhibition of efflux. Preincubation with 40 mm ethanol for 45 min resulted in a significantly increased rate of entry of 5-methyltetrahydrofolate into the cells. The stimulatory effect was specific to 5-methyltetrahydrofolate since ethanol inhibited uptake of folate and methotrexate. The increased uptake was due to metabolism of ethanol as shown by studies with pyrazole. Also, the n-alkanols, propanol through pentanol, and sorbitol but not methanol were stimulatory. Anaerobiosis and sodium azide stimulated uptake of 5-methyl-tetrahydrofolate but were inhibitory to methotrexate uptake. These data, taken together, suggest that the ethanol effect is due to increased entry of 5-CH₃-H₄PteGlu into the cells possibly as the result of an increased cellular $\text{NADH}\text{NAD}$ ratio.     

The effects of temperature and host density on the development and survival of Copidosoma koehleri

Developmental rates for Copidosoma koehleri Blanchard (Hymenoptera: Encyrtidae) and its host, Phthorimaea operculella (Zeller), were determined at 10, 15, 23, 27, 29, 32, 34 and 35°C from host egg to adult. The developmental rates determined for both species showed good fit to mathematical models of insect development. At 15°C mean emergence of adult C. koehleri was 15 days after P. operculella adults emerged. At 29°C mean emergence of C. koehleri was only 5 days after that of P. operculella. P. operculella developed at 35°C, but parasitized larvae, and therefore C. koehleri, did not tolerate temperatures above 32°C. In the presence of C. koehleri, host survival was low (3%) at low host egg densities, but greater (20%) at higher host densities. Parasitized larvae of P. operculella were less able to compete for food resources, as measured by adult emergence.     

Relationship of macromolecular synthesis to competence induction in a group H streptococcus.

Group H streptococcus strain Wicky, which was induced to competence for genetic transformation with competence factor (CF) derived from a related strain, displayed reduced rates of ribonucleic acid (RNA) and peptidoglycan synthesis. Pulse-labeling studies revealed that the inhibition of both RNA and peptidoglycan synthesis was maximal at the peak of competence and decreased as competence declined. These studies indicated that competence induction had only a slight effect on the rate of protein synthesis. Trypsin inactivation of CF prevented the reductions in synthesis normally elicited by CF preparations. If the addition of trypsin was delayed until 5 min after the addition of CF, competence induction and decreased synthesis of RNA and peptidoglycan were again apparent. Thus, the alterations in the synthesis of these macromolecules appeared to be related to the induction of competence. Further studies indicated that the apparent reductions in biosynthesis were not caused by decreased uptake of the labeled precursors by intact Wicky cells. In addition, these effects were probably not the result of turnover of macromolecules induced by CF. The lack of turnover of labeled peptidoglycan suggested that competence induction may not involve an autolysin.