Inhibition of brain hexokinase by a multisubstrate analog results from binding to a discrete regulatory site

P1-(adenosine-5')-P3-(glucose-6)-triphosphate (Ap3glucose) is a linear uncompetitive inhibitor vs glucose and a linear mixed inhibitor vs ATP of brain hexokinase, an inhibition pattern inconsistent with binding of Ap3glucose to the catalytic site when either the rapid equilibrium random or ordered sequential mechanism, which have been proposed for this enzyme, is considered. It is concluded that inhibition results from binding to a discrete regulatory site. The apparent ability of the regulatory site to accommodate both hexose and nucleotide moieties is consistent with suggestions by previous investigators that the regulatory site on mammalian hexokinases may have evolved from what was originally a catalytic site.     

The evolution of dominance: Haldane v Fisher revisited.

Fisher's model for the evolution of dominance indicates that the accumulation of dominance modifiers will be accelerated by (1) an increased frequency of the mutant heterozygote, (2) increased selection for the phenotype of the normal homozygote. The model has been criticised by Haldane on the grounds that point (1) is not fulfilled, that is dominance appears to be more common in populations with a low frequency of mutant heterozygotes (populations of inbreeders). In support of Fisher's model it is argued that intense selection for the wild type phenotype is more common in inbreeders than outbreeders. This situation should promote the accumulation of dominance modifiers (point (2) above).     

The Wolff-Parkinson-White Pattern in Routine Electrocardiography

Fifteen thousand consecutive electrocardiograms on R.C.A.F. aircrew applicants aged 18 to 24 were studied from the standpoint of incidence, clinical findings and follow-up of the WPW pattern discovered because the ECG was taken as part of the selection procedure. Forty-six cases were discovered (0.3%). All were reviewed and passed as clinically fit except for one with asymptomatic rheumatic heart disease. Two others gave a history suggestive of paroxysmal rapid heart action. None of the 43 men on follow-up have developed evidence of arrhythmia. Thirteen of the 46 showed an intermittent pattern initially or on subsequent follow-up. Fifty to 80% of people with the WPW pattern experience tachycardia, according to the literature. The incidence of tachycardia in this study was much lower (2 in 46 or 4.3%). The WPW pattern is not synonymous with the WPW syndrome, and iatrogenic heart disease must be avoided in fit young men in whom the WPW pattern is discovered because of routine electrocardiography.     

Unsupervised Learning of Cone Spectral Classes from Natural Images

The first step in the evolution of primate trichromatic color vision was the expression of a third cone class not present in ancestral mammals. This observation motivates a fundamental question about the evolution of any sensory system: how is it possible to detect and exploit the presence of a novel sensory class? We explore this question in the context of primate color vision. We present an unsupervised learning algorithm capable of both detecting the number of spectral cone classes in a retinal mosaic and learning the class of each cone using the inter-cone correlations obtained in response to natural image input. The algorithm''s ability to classify cones is in broad agreement with experimental evidence about functional color vision for a wide range of mosaic parameters, including those characterizing dichromacy, typical trichromacy, anomalous trichromacy, and possible tetrachromacy.     

Defective growth functions in mutants of Escherichia coli K12 lacking a major outer membrane protein.

Various properties of mutants of Escherichia coli K12 lacking specific outer membrane proteins have been studied. ompA mutants are shown to grow less well than their parent strains under a variety of growth conditions, and after completion of growth to enter a decline phase in which viability is lost and the cells become heavily piliated and clump. They are defective in the uptake of amino acids, whereas the uptakes of the larger transport substrates ferrienterochelin and cyanocobalamin (vitamin B12) are normal. These ompA mutants also grow poorly at 42 °C. The implications of these results are discussed in terms of the function of the ompA. gene product. No growth or uptake defects were observed for ompB or tsx mutants.     

Lymphoid organ development in Xenopus thymectomized at eight days of age

This paper examines the effect of early thymectomy on the subsequent development of lymphoid tissues in the toad, Xenopus laevis. At the time of thymic removal (8 days post-fertilization) all the lymphoid organ anlagen are at a rudimentary state of differentiation and contain few, if any, small lymphocytes. Despite the absence of any thymic tissue all thymectomized animals grew normally. Thymectomized larvae developed relatively normal lymphoid organs. However, lymphoid depletion was apparent in the splenic red pulp and in the pharyngeal ventral cavity bodies. Examination of the lymphoid organs of post-metamorphic Xenopus revealed reduction in spleen size following thymectomy. Lymphoid depletion was evident in the splenic red pulp of many thymectomized toadlets and reduction in proportion of white to red pulp was also noted in a few of these animals. Absence of the thymus had no apparent effect on the histology of the other lymphoid organs examined.