Availability of avidin-bound biotin to the chicken embryo.

Avidin, an exceptionally stable protein in egg white, binds the vitamin biotin with very high affinity and can induce biotin deficiency when fed to animals. To determine if biotin bound to avidin is available to the chicken embryo, the fate of [3H]biotin complexed to avidin was monitored during embryonic development. The majority (greater than 85%) of the [3H]biotin was extraembryonic until the day before hatching, when embryos swallow egg white and withdraw the yolk sac into their abdomen. Thus, biotin in the egg white of chicken eggs contributes little to the biotin status of the chick prior to hatching. After hatching, much of the [3H]biotin was assimilated. About 30% of the total was found in the liver and kidneys by 4 days of age. The biotin in liver was associated with large proteins and not with avidin. In a separate experiment, biotin injected into the egg white of biotin-deficient eggs failed to increase embryonic development or hatchability. Both experiments suggest that biotin in egg yolk is the primary and virtually sole source of biotin for the chicken embryo.

Competitive binding assays for high-affinity binders in the presence of endogenous ligands: application to biotin-binding proteins.

Endogenous ligands complicate radioligand-binding assays of high-affinity binding proteins by obscuring binding sites or by diluting the labeled ligand. We have developed a mathematical model for such systems where radioligand and endogenous ligand are structurally identical. Data which relate radioligand binding at equilibrium as a function of sample volume can be plotted such that the concentrations of endogenous ligand and binder are graphically determined; however, a more precise determination may be done by nonlinear regression with the aid of a microcomputer. The method is demonstrated for the assay of biotin-binding proteins in the presence of a range of endogenous biotin concentrations below and above that required to saturate the binding sites.

Biotin diffusion in stored chicken eggs: a re-assessment.

1. The possibility that biotin in stored eggs migrates from the yolk into the albumen was re-investigated. 2. Sets of eggs collected from 12 Single Comb White Leghorn hens were stored at 5, 8, 12, 15, or 18 degrees C for 5, 10, 15, 20, or 25 days and then frozen. 3. For each set, yolk and albumen samples adjacent to the yolk membrane were each pooled and assayed for protein-bound biotin by radioligand exchange with non-linear regression analysis of the data. 4. In contrast to previous work reported by Bush and White (Comp. Biochem. Physiol. 93B, 543-547, 1989), no evidence of biotin diffusion was found. 5. Non-linear regression was used to re-evaluate the data from the earlier study, confirming the results, although less strikingly. 6. The discrepancy is partly due to the method of data analysis, although differences in breed or number of hens may also be contributing factors.

Central pacific seabirds and the el nino southern oscillation: 1982 to 1983 perspectives.

The breeding chronology and reproductive attempts of the seabird community on Christmas Island in the central Pacific Ocean (2 degrees N, 157 degrees W) were interrupted by the 1982-1983 El Niño Southern Oscillation. The resultant reproductive failure and disappearance of the entire seabird community of this equatorial atoll represents the most dramatic interruption on record of a seabird community located distant from coastal upwelling. Our data indicate the effect that the abiotic and biotic aspects of a global atmospheric-oceanic anomaly have on marine birds. The 1982-1983 El Niño Southern Oscillation provides an example of selective pressures and a natural experiment in the study of vertebrate population dynamics.

Nucleic acid synthesis in the chloroplasts of Acetabularia mediterranea.

Radioautographic and radiochemical techniques were used to establish the presence of replicating DNA in the chloroplasts of Acetabularia mediterranea. These techniques also demonstrated that these chloroplasts synthesize RNA. It was found that label from thymine was also incorporated into DNA and RNA in these chloroplasts. With the establishment of protein and nucleic acid synthesis in Acetabularia chloroplasts, it is clear that these chloroplasts carry out those metabolic processes which are most characteristic of autonomous cells.