The number of catalytic sites in acetylcholinesterase

By using two methods of titration, the number of active sites in acetylcholinesterase was determined. Either stepwise inhibition of the enzyme by an irreversible inhibitor, namely di-isopropyl phosphorofluoridate, or direct measurement of the concentration of active sites by titration with o-nitrophenyl dimethylcarbamate yielded an equivalent weight of approx. 130000 for an active site in acetylcholinesterase. This indicates two sites per molecule, since the native enzyme has a molecular weight of 260000.     

Some thoughts on the requirements for a theory of biology

Complexity and stability are the ubiquitous characteristics of all biological phenomena. The theoretical suggestions presented here acknowledge this and attempt to capitalize on the property of selectiveness that complexity induces. It is from this that a belief in the existence of selection rules emerges. What is required of a viable theory is a linguistic means of maneuvering known information so that these selection or limitation rules may be obtained, and thence, by their manipulation, to generate the properties exhibited by biological systems.     

Experimental chemotherapy of radiation injury with synthetic lysophospholipid analogs in mice

Synthetic lysophospholipids represent a variety of analogs of the naturally occurring 2-lysophosphatidylcholine. Some of these compounds showed significant therapeutic effects on the survival of mice following radiation injury when administered after various doses of whole-body X irradiation. Such therapeutic effects were discernible even when the treatment was given 6 hr after irradiation, and both intravenous and oral application were effective. Intravenous application of 2 X 25 mg/kg lysophospholipid after whole-body X irradiation around the LD50 resulted in significantly higher numbers of surviving animals. The mode of action remains speculative.     

The milky spots on the chest wall in newborns

The histologic properties of pleural adipose organs were studied in 14 newborns. These organs contain milky spots, in which lymphocytes, macrophages and plurivacuolated fat cells are present. The milky spots have a mesothelial covering, persist to the age of 9 months and seem to act as defence devices and a site of fluid exchange.     

A convenient program for the rapid calculation of sedimentation coefficients in linear salt or sucrose gradients

A program is presented for calculating s_20,w values from data obtained by zone sedimentation in linear sucrose or salt gradients in a variety of rotors at temperatures ranging from 0° to 20°C. The program can be either run with the use of high-speed computers or performed with the aid of a small calculator in a reasonably short time.