Genic homozygosity in an ancient reptile (Alligator mississippiensis)

Proteins assayed electrophoretically showed variation at only three of 49 presumed genetic loci in alligators from southwestern Louisiana. Average heterozygosity per individual was 0.021±0.012; proportion of polymorphic loci was 0.06. Data on the history, structure, and ecology of this alligator population are consistent with natural selection as the primary factor accounting for this low genetic variability. However, neither a historic population bottleneck nor some genetic mechanism limiting variability can be dismissed as a possible factor.The study was supported by NSF Grant BMS 73-0125 to H.C.D.     

A CD determination of the alpha-helix contents of the coat proteins of four filamentous bacteriophages: fd, IKe, Pf1, and Pf3

The CD spectra of four filamentous bacteriophages--fd, IKe, Pf1, and Pf3--were analyzed to determine the alpha-helix contents of their major coat proteins. Measured spectra included the 192-nm band so that analyses could be carried out over the full wavelength range of the reference spectra for protein secondary structures available (a) from globular proteins [J.T. Yang, C.S.C. Wu, and H.M. Martinez (1986) Methods in Enzymology 130, 208-269] and (b) from poly(L-lysine) [N. Greenfield and G.D. Fasman (1960) Biochemistry 8, 4108-4116]. Extended analyses were also performed with the addition of the spectrum of a model beta-turn to the Greenfield and Fasman reference set, with the spectrum of a short alpha-helix in the Yang et al. reference set, and with an estimate of the spectrum of Trp added to both reference sets. The reference set based on the simple poly(L-lysine) polypeptide, plus a spectrum of a model beta-turn or of Trp, gave reasonably good fits to the measured spectra for all four phages and yielded the largest percentages of alpha-helix. The class I phages--fd and IKe--had large percentages of alpha-helix of 98 +/- 2 and 97 +/- 5%, respectively, while the two class II phages--Pf1 and Pf3--had similar but smaller alpha-helix contents of 83 +/- 6 and 84 +/- 2, respectively. While these alpha-helix contents were within the ranges previously reported from CD spectra of these phages in solution, they were more precise, and they indicated that the coat proteins of the intact phages have CD spectra that are probably modeled better by the reference spectra of polypeptides than by those of globular proteins.     

Light-evoked walking in crayfish: Behavioral and neuronal responses triggered by the caudal photoreceptor

The caudal photoreceptors (CPRs) of crayfish (Procambarus clarkii) can trigger walking and abdominal movements by their response to light.

Strategic procurement of fish by the pumé: A South American “fishing culture”

Information is presented on fishing effort, efficiency, techniques, and catch composition for Pumé men, women, and children along with a conceptual model of fishing as a food procurement strategy. The Pumé are a native lowland South American group living in the topical savanna region of southwestern Venezuela characterized by seasonal flooding. Results are discussed in relation to the Pumé environmental and social situation, and briefly compared with results from other lowland South American groups.     

Permeability of the squid giant axon to organic cations and small nonelectrolytes

Summary The permeability of the Na channel of squid giant axon to organic cations and small nonelectrolytes was studied. The compounds tested were guanidinium, formamidinium, and¹⁴C-labeled urea, formamide, thiourea, and acetone. Permeability was calculated from measurements of reversal potential and influx on internally perfused, voltage clamped squid axons. The project had two objectives: (1) to determine whether different methods of measuring the permeability of organic cations yield similar values and (2) to see whether neutral analogs of the organic cations can permeate the Na channel. Our results show that the permeability ratio of sodium to a test ion depends upon the ionic composition of the solution used. This finding is consistent with the view put forward previously that the Na channel can contain more than one ion at a time. In addition, we found that the uncharged analogs of permeant cations are not measurably permeant through the Na channel, but instead probably pass through the lipid bilayer.