them to locate specific cell-cell attachment sites 

 and the release sites for secretory vesicles. 

 Knowledge of membrane composition is now 

 being integrated with the intricate details of mem- 

 brane structure. 



Artificial membranes. Among the remarkable 

 achievements has been the development of tech- 

 niques to make artificial membranes. Lipid bilay- 

 ers of known composition can be formed in sever- 

 al ways. Techniques have been devised recently 

 to make bilayers with differing compositions in 

 the outer and inner halves of the bimolecular leaf- 

 let. Selected membrane proteins can be incorpo- 

 rated into either or both halves of the leaflet. 

 Chemical, electrical, and spectroscopic measure- 

 ments can be made on these artificial membranes. 

 One class of artificial membranes, liposomes, can 

 be taken up by some cells and thus allow the in- 

 troduction of enzymes and pharmacological 

 agents into these cells. 



Membrane transport. This entire battery of new 

 techniques has enabled researchers to .study the 

 transport of materials across membranes in ex- 

 quisite detail. It has been possible to investigate 

 the energetics, kinetics, and selectivity of active 

 transport of molecules in living cells. In some 

 cases researchers have been able to purify a spe- 

 cific transport protein and incorporate it into arti- 

 ficial membranes where it will perform as in vivo. 

 The study of passive transport of molecules 

 across membranes has also expanded markedly. 

 In addition to physiological transport proteins, 

 several natural and synthetic antibiotics have been 

 found to facilitate ion transport across mem- 

 branes. Investigators have accumulated extensive 

 knowledge about the molecular details of trans- 

 port: the shape of the transporting structure, its 

 relationship to the lipid, the energetics of the fa- 

 cilitation of ion flow, the basis for the ionic selec- 

 tivity, and the kinetics of the flow. 



Membrane biogenesis. How membranes are 

 formed in the cell is little understood. The neces- 

 sary techniques and the appropriate questions are 

 just now being developed. There are some indica- 

 tions that plasma membranes can be formed from 

 vesicles that have broken off from the endoplasm- 

 ic reticulum and related intracellular membranes. 

 A class of proteins has recently been discovered 

 that can exchange lipid molecules between mem- 

 branes in difl'erent parts of the cell. Whether these 

 lipid transport proteins are involved in membrane 

 synthesis, repair, or some completely unexpected 

 function is not known. Several membrane pro- 

 teins that span the membrane have been isolated 

 and sequenced. In all these cases the amino-ter- 

 minal end of the protein sticks out into the extra- 

 cellular space while the carboxy-terminal end pro- 



jects into the cytoplasm. Since the amino-terminal 

 end of a peptide is always the part made first on 

 the ribosome, it is hypothesized that the mem- 

 brane proteins are synthesized directly on a mem- 

 brane and extruded sequentially through the 

 membrane during synthesis. This area of research 

 is just beginning to be explored. 



Slow Viruses and Neurologic Diseases 



An important recent accomplishment in biomed- 

 ical research is recognition of the role played by 

 what are known as "slow" or "latent" viruses in 

 disorders of the central nervous system. These 

 pathogens are viral-type agents that require a long 

 course of action — months or years — before the 

 consequences of the infection become manifest in 

 illness or disturbed function. The first recognition 

 of their delayed action in human disease came 

 from a study of kuru, a severe motor disability 

 resulting from cerebellar degeneration that oc- 

 curred only among isolated tribes of natives in the 

 highlands of New Guinea. 



For his discovery that kuru and another dege- 

 nerative and dementing disorder of the human 

 nervous system can be caused by transmissible 

 virus-like agents. Dr. D. Carleton Gajdusek of the 

 National Institute of Neurological and Communi- 

 cative Disorders and Stroke (NINCDS) was 

 awarded the 1976 Nobel Prize in medicine. The 

 Nobel award also recognized Dr. Gajdusek's dis- 

 covery that the agents causing these two diseases 

 and two other neural disorders in animals are 

 pathogens with properties unlike any known bac- 

 teria or viruses and may well represent a com- 

 pletely new biological phenomenon. 



In living and working with the natives of New 

 Guinea, Dr. Gajdusek considered that kuru might 

 be a unique form of infection that was transmitted 

 during the ceremonies of ritualistic cannibalism by 

 which the natives honored their dead. When he 

 returned to the United States to head the Labora- 

 tory of Slow, Latent, and Temperate Virus Infec- 

 tions at NINCDS, he embarked on an extensive 

 program of inoculating kuru brain material into 

 laboratory animals to discover the causative agent 

 of the disease. There were many unsuccessful 

 inoculations, but finally several chimpanzees de- 

 veloped a disease identical to kuru two or three 

 years after inoculation. Dr. Gajdusek was then 

 able to transmit the kuru agent from these chim- 

 panzees to others, with progressive shortening of 

 the latent period. He has since confirmed this 

 observation many times, and has conclusively 

 proved that the kuru agent is unlike any known 

 organism in man and is a completely unique type 

 of human pathogen. 



This work suggested the possibility that many 



HEALTH, EDUCATION AND WELFARE 101 



