Band Gap Shift of GaN under Uniaxial Strain Compression

The band-gap shift of GaN:Mg epilayers on (0001)-oriented sapphire was studied as a function of uniaxial strain compression along the c-axis using time-resolved, optical absorption measurements in shock wave experiments. For longitudinal stresses ranging from 4 to 14 GPa, the band gap shift is approximately 0.026 eV/GPa. Combining this result with the known behavior of wurtzite GaN under hydrostatic pressure and biaxial stress, a new set of deformation potentials has been estimated: acz-D1 = -10.2 eV, act-D2 = -7.9 eV, D3 = 1.33 eV and D4 = -0.74 eV. A slow band gap shift is also observed following the immediate band gap increase upon impact. This phenomenon can be explained by a time-dependent screening of the piezoelectric field.

Formation of the Antithrombin Heterodimer In Vivo and the Onset of Thrombosis

Antithrombin is shown to undergo a slow spontaneous conversion to its inactive latent conformation with readily discernible amounts present in plasma on incubation at 37°C for 72 hours. More rapid conversion occurs on incubation of isolated antithrombin at 41°C or 50°C, but the appearance on electrophoresis of free latent antithrombin is preceded by the formation, in reciprocal proportions, of a new slow band. This slow component is shown to be a heterodimer of active and latent antithrombin. It can be isolated as a single stable band either by incubation of antithrombin or by mixing equimolar proportions of active and latent antithrombin under the same conditions that give overnight crystallization of the active/latent antithrombin heterodimer. Similarly, equimolar addition of latent antithrombin to plasma results electrophoretically in a quantitative shift to the slower heterodimer mobility. Clinically, the presence of latent antithrombin is potentially deleterious, because its linkage to form the heterodimer results in inactivation of the otherwise normal molecule linked to the latent antithrombin. In the case of -antithrombin, because the dimer readily dissociates, there is only a 11% additive loss of activity, but with β-antithrombin the dimer appears more stable, with the additive loss of activity from the normal β component being 21%, increasing to 33% on stabilization of the dimer with heparin. This linked and selective loss of activity of β-antithrombin provides an explanation for the unexpected severity of thrombotic episodes in heterozygotes with conformationally unstable antithrombins.

Inheritance of Phosphoglucoisomerase in Fountain Grass

Starch gel electrophoresis was used to screen 10 enzyme systems for variation in fountain grass, Pennisetum alopecuroides (L.) Spreng. plants exhibiting four different growth habits: dwarf(d), mound(m), prostrate(p), and upright (u). Only phosphoglucoisomerase (PGI; E.C. 5.3.1.9) was found to be polymorphic at one locus, PGI-2, and was expressed as two alleles, which appeared to be associated with growth habit. The dwarf form expressed one slow band (SS), the mound and prostrate forms exhibited one fast band (FF), and the upright form carried triple bands indicating a heterodimer (FS). Hybrids between FF and SS parents were detected as triple bands (FS). Three generations of progeny resulting from 16 crosses and selfs of these growth habits all followed the expected segregation ratios for typical Mendelian inheritance of this isozyme.

Isozymes of amylase, alcohol dehydrogenase, malic enzyme, malate dehydrogenase, and superoxide dismutase in Chloealtis conspersa (Orthoptera)

Five enzymes of the grasshopper Chloealtis conspersa were studied for possible gene linkage. Because of the extreme localization of chiasmata throughout most of the genome of C. conspersa, it was expected that genes would appear either to be completely linked or to assort independently. Our results indicate that malic enzyme and alcohol dehydrogenase are probably on the X chromosome. Superoxide dismutase is produced from the product of duplicate genes where Sod 1-1 is monomorphic and Sod 1-2 has two alleles, one producing a fast-migrating band on gel electrophoresis and one a slow band. While amylase, malate dehydrogenase, and superoxide dismutase appeared to be autosomal, there was no evidence of linkage between them.Key words: Chloealtis conspersa, amylase, alcohol dehydrogenase, malic enzyme, malate dehydrogenase, superoxide dismutase.

Regenerative fidelity in the paired claw closer muscles of lobsters

The paired claws in the lobster Homarus americanus are bilaterally asymmetric, consisting of a major (crusher) and a minor (cutter) claw. The fiber composition of the claw closer muscles is correspondingly asymmetric: the cutter muscle has predominantly fast fibers with a small ventral slow band, whereas the crusher muscle has 100% slow fibers. Loss of the paired claws results in regeneration of new ones, which resemble their predecessors in external morphology and in the fiber composition of the closer muscle. Such regenerative fidelity prevails even when the paired claws and closer muscles are symmetric and of the cutter type, and even when they have undergone two successive cycles of limb loss and regeneration. Therefore the type of closer muscle and the configuration of the paired claws is not altered by loss and regeneration.

Detection of alkaline phosphatase/immunoglobulin complexes.

We report another patient with a circulating alkaline phosphatase/immunoglobulin complex in his blood, and describe a simple method of demonstrating such complexes. On electrophoresis on cellulose acetate, the complex was relatively slow moving and there was no activity in the normal bone/liver isoenzyme region. When the serum was treated with trypsin, the slow band disappeared and the normal pattern was restored.

The electrophoretically ‘slow’ and ‘fast’ forms of the α2-macroglobulin molecule

alpha 2-Macroglobulin (alpha 2M) was isolated from human plasma by a four-step procedure: poly(ethylene glyco) fractionation, gel chromatography, euglobulin precipitation and immunoadsorption. No contaminants were detected in the final preparations by electrophoresis or immunoprecipitation. The protein ran as a single slow band in gel electrophoresis, and was designated ‘S-alpha 2M’. S-alpha 2M bound about 2 mol of trypsin/mol. Treatment of S-alpha 2M with a proteinase or ammonium salts produced a form of the molecule more mobile in electrophoresis, and lacking proteinase-binding activity (F-alpha 2M). The electrophoretic mobility of the F-alpha 2M resulting from reaction with NH4+ salts was identical with that of proteinase complexes. We attribute the change in electrophoretic mobility of the alpha 2M to a conformation change, but there was no evidence of a change in pI or Strokes radius. Electrophoresis of S-alpha 2M in the presence of sodium dodecylsulphate gave results consistent with the view that the alpha 2M molecule is a tetramer of identical subunits, assembled as a non-covalent pair of disulphide-linked dimers. Some of the subunits seemed to be ‘nicked’ into two-thires-length and one-third-length chains, however. This was not apparent with F-alpha 2M produced by ammonium salts. F-alpha 2M produced by trypsin showed two new bands attributable to cleavage of the subunit polypeptide chain near the middle. Immunoassays of F-alpha 2M gave ‘rockets’ 12-29% lower than those with S-alpha 2M. The nature of the interactions between subunits in S-alpha 2M and F-alpha 2M was investigated by treating each form with glutaraldehyde before electrophoresis in the presence of sodium dodecyl sulphate. A much greater degree of cross-linking was observed with the F-alpha 2M, indicating that the subunits interact most closely in this form of the molecule. Exposure of S-alpha 2M to 3 M-urea or pH3 resulted in dissociation to the disulphide-bonded half-molecules; these did not show the proteinase-binding activity characteristic of the intact alpha 2M. F-alpha 2M was less easily dissociated than was S-alpha 2M. S-alpha 2M was readily dissociated to the quarter-subunits by mild reduction, with the formation of 3-4 new thiol groups per subunit. Inact reactive alpha 2M could then be regenerated in high yield by reoxidation of the subunits. F-alpha 2M formed by reaction with a proteinase or ammonium salts was not dissociated under the same conditions, although the interchain disulphide bonds were reduced. If the thiol groups of the quarter-subunits of S-alpha 2M were blocked by carboxymethylation, oxidative reassociation did not occur. Nevertheless treatment of these subunits with methylammonium salts or a proteinase caused the reassembly of half-molecules and intact (F-) tetramers. It is emphasized that F-alpha 2M does not have the properties of a denatured form of the protein…

Tissue-characteristic forms of glyceraldehyde 3-phosphate dehydrogenase

Glyceraldehyde 3-phosphate dehydrogenase exists in two different forms in various human tissue preparations. One of them is exhibited, after starch-gel electrophoresis, by a rapidly migrating or `fast' band and the other by a `slow' band. The proportion of the total activity in each of the two forms is characteristic of the type of tissue. A particulate fraction, obtained after centrifugation of homogenates, inhibits the enzyme activity and tends to convert the slow band into a fast one. The conversion is reversible. The fast band can also be converted into the slow one by addition of NAD+ or ADP, or by dialysis against saturated sodium chloride solution. Conversions occur with the purified enzyme as well as with crude homogenates. The relevance of these findings to previous investigations and to glycolytic control mechanisms are discussed.

A SERUM POST ALBUMIN SYSTEM IN MINK

Two post albumin bands in the sera of mink have been observed by horizontal starch-gel electrophoresis, a fast band, designated A, and a slow band, designated B. It is proposed that this system is composed of 2 alleles, PaA and PaB, giving rise to 3 phenotypes, PaA, PaB and PaAB. The results of tests of sera from progeny from 16 matings is in agreement with this genetic hypothesis.