Alpha galactosidase

26 Mar

Alpha galactosidase 
allophene  a phenotype not due to the mutant ge- netic constitution of the cells of the tissue in ques- tion. Such a tissue will develop a normal phenotype if transplanted to a wild-type host. See autophene.

allophenic mice  chimeric mice produced by re- moving cleaving eggs from mice of different geno- types, fusing the blastomeres in vitro, and reim- planting  the  fused  embryos  into  the  uterus  of another mouse to permit embryogenesis to continue.

Viable mice containing cells derived from two or more embryos have been obtained and used in cell lineage studies. See Appendix C, 1967, Mintz. alloplasmic  referring to organisms or cells bearing chromosomes of one species and cytoplasm of a dif- ferent species; for example, bread wheat (Triticum aestivum) chromosomes and rye (Secale cereale) cy- toplasm. Compare with heteroplasmic, heteroplas- tidy.

allopolyploid (also alloploid)  a polyploid organ- ism arising from the combination of genetically dis- tinct chromosome sets. See isosyndetic alloploid, seg- mental alloploid.

alloprocoptic  selection  a mode of selection in which association of opposites increases the fitness of the associates. An example involves the loci gov- erning alcohol dehydrogenase in Drosophila melano- gaster. The fertility is greater than expected when two mating individuals are homozygous for different alleles and smaller than expected when they are ho-

Alpha galactosidase

mozygous for the same allele. allostery  the reversible interaction of a small mol- ecule  with  a  protein  molecule,  which  leads  to changes in the shape of the protein and a consequent alteration of the interaction of that protein with a third molecule.

allosteric effectors  small molecules that revers- ibly bind to allosteric proteins at a site different from the active site, causing an allosteric effect. allosteric enzyme  a regulatory enzyme whose cat- alytic activity is modified by the noncovalent attach- ment of a specific metabolite to a site on the enzyme other than the catalytic site. allosteric protein  a protein showing allosteric ef- fects.

allosteric site  a region on a protein other than its active site (q.v.), to which a specific effector mole- cule may bind and influence (either positively or negatively) the functional activity of the protein. For example, in the lactose system of E.

coli, the lac re- pressor becomes inactive (cannot bind to the lac op-erator) when allolactose is bound to the allosteric site of the repressor molecule. See lac operon. allosyndesis  the pairing of homoeologous chro- mosomes (q.v.) in an allopolyploid (q.v.).

Thus if the genetic  composition  of  an  alloploid  is  given  by AABB, where AA represent the chromosomes de- rived from one parent species and BB the chromo- somes derived from the other parent species, then during meiotic prophase, A undergoes allosyndetic pairing with B.

Such pairing indicates that the A and B chromosomes have some segments that are ho- mologous, presumably because the two parent spe- cies have a common ancestry. In the case of autosyn- desis, A pairs only with A, and B with B.

Segmental alloploids form both bivalents and multivalents dur- ing meiosis because of allosyndesis. allotetraploid  an organism that is diploid for two genomes, each from a different species; synonymous with amphidiploid (q.v.). allotypes  proteins that are products of different alleles of the same gene. The term is often used to refer to serologically detectable variants of immu- noglobins and other serum proteins.

allotype  suppression  the  systematic  and  long- term suppression of the expression of an immuno- globulin allotype in an animal induced by treatment with antibodies against the allotype. allotypic differentiation  See in vivo culturing of imaginal discs.

allozygote  an individual homozygous at a given locus, whose two homologous genes are of indepen-dent origin, as far as can be determined from pedi-gree information. See autozygote. allozymes  allelic forms of an enzyme that can be distinguished by electrophoresis, as opposed to the more general term isozyme (q.v.).

See Appendix C, 1966, Lewontin and Hubby. alpha amanitin  See amatoxins. alpha chain  one of the two polypeptides found in adult and fetal hemoglobin (q.v.). alpha fetoprotein  the major plasma protein of fe- tal mammals. AFP is a 70-kilodalton glycoprotein that is synthesized and secreted by the liver and the yolk sac.

The genes encoding AFP and serum albu- men arose in evolution as the result of a duplication of an ancestral gene (3-5) × 108  years ago. See al- bumen. alpha galactosidase  an enzyme that catalyzes the hydrolysis of substrates that contain α-galactosidic residues, including glycosphingolipids and glycopro-

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