The time of greatest sensitivity to radiation is during the period of organogenesis in the first twelve weeks of human foetal development. Irradiation of the adult can cause life shortening or increased incidence of leukemia. The last chapter is concerned with the basis and origin of radiation protection standards, the hazards of nuclear power plants, high altitude supersonic aerospace travel, ...

At various postnatal stages, intestinal epithelial cells were isolated sequentially from villus tip to crypt base by successive EDTA treatments. According to the localization of marker enzymic activities, isolated cells were pooled into three cell compartments: villus (V), lower villus and upper crypt (VC) and crypt (C). Purified brush-border-membrane proteins were separated by 7.5%-polyacrylam...

The intracellular distribution and level of acid hydrolases in Ochromonas malhamensis were studied in cells grown osmotrophically in a defined medium, in a carbon-free starvation medium, and during phagotrophy in each of these media. By cytochemical techniques, little enzymic reaction product was observed in the vacuoles of osmotrophic cells grown in the defined medium. Starved cells, however, ...

Copper can be removed from bovine cytochrome c oxidase with bathocuproine disulfonate under anaerobic conditions in the presence of reduced cytochrome c. The copper-depleted enzyme is relatively inactive. Upon replacement of copper with Cu’-acetonitrile, more than the original activity is regained. The rate of O2 consumption catalyzed by the reconstituted enzyme is unaffected by catalase; the p...

Amniocentesis was performed in the 15th week of a pregnancy at risk for Wolman's disease. The cultured amniotic fluid cells were found to have a severe deficiency of acid esterase activity consistent with homozygosity of the fetus. The pregnancy was terminated in the 19th week and the prenatal diagnosis confirmed by enzymic and chemical evaluation of the fetal tissues.

Human or rat microsomal 5 alpha-reductase activity, as measured by enzymic conversion of testosterone into 5 alpha-dihydrotestosterone or by binding of a competitive inhibitor, [3H]17 beta-NN-diethulcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one ([3H]4-MA) to the reductase, is inhibited by low concentrations (less than 10 microM) of certain polyunsaturated fatty acids. The relative inhibitory...

Acetylcholinesterase (AChE) activity has been studied in the myoblast of skeletal muscle of the 9-13 day fetal rabbit. Cytochemical activity is present in the nuclear envelope and the endoplasmic reticulum, including its derivatives the subsurface reticulum and the sarcoplasmic reticulum. End product is also found in the Golgi complex of the more differentiated myoblasts. The formation of retic...

Substrate- and ligand-induced conformational changes were studied in a series of thiol-modified derivatives of rabbit muscle creatine kinase that retained different amounts of enzymic activity. The results indicate that the 'reactive' thiol group of the enzyme is required for the conformational changes associated with formation of a 'transition-state analogue' complex.

Ammodytoxins (Atxs) are group II phospholipases A(2) (PLA(2)s) with presynaptic toxicity from venom of the snake Vipera ammodytes ammodytes. The molecular basis of their neurotoxicity, and that of similar PLA(2) toxins, is still to be explained. To address this problem, a surface-exposed aromatic residue, Phe(24), in the N-terminal region of the most potent Atx, AtxA, was replaced by other arom...