Parallel access read/write memory using an optically addressed ferroelectric spatial light modulator.

The ability is demonstrated to use optically addressed ferroelectric spatial light modulators in designing digital optical computers involving data processing and storage athigh rates and contrast levels. Key words: Bistability, ferroelectric SLM, parallel access memory.

Synthesis and characterization of a new fluorogenic active-site titrant of serine proteases.

The molecule 3',6'-bis(4-guanidinobenzoyloxy)-5-[N'-(4-carboxyphenyl)thioureido[spirop]isobenzofuran-1-(3H),9'-[9H]xanthen]-3-one, abbreviated FDE, was designed and synthesized as a fluorogenic active-site titrant for serine proteases. It is an analogue of p-nitrophenyl p-guanidino-benzoate (NPGB) in which a fluorescein derivative is substituted for p-nitrophenol. FDE and NPGB exhibit similar kinetic characteristics in an active-site titration of trypsin in phosphate-buffered saline, pH 7.2. The rate of acylation with FDE is extremely fast (k2 = 1.05 s-1) and the rate of deacylation extremely slow (k3 = 1.66 X 10(-5) s-1). The Ks is 3.06 X 10(-6) M, and the Km(app) is 4.85 X 10(-11) M. With two of the serine proteases involved in fibrinolysis, the rate of acylation with FDE is also fast, K2 = 0.112 s-1 for urokinase and 0.799 s-1 for plasmin, and the rate of deacylation is slow, k3 = 3.64 X 10(-4) s-1 for urokinase and 6.27 X 10(-6) s-1 for plasmin. The solubility limit of FDE in phosphate-buffered saline is 1.3 X 10(-5) M, and the first-order rate constant for spontaneous hydrolysis is 5.1 X 10(-6) s-1. The major difference between FDE and NPGB is the detectability of the product in an active-site titration. p-Nitrophenol can be detected at concentrations no lower than 10(-6) M whereas fluorescein can be detected at concentrations as low as 10(-12) M. Thus, FDE should be useful in quantitatively assaying serine proteases as very low concentrations.

Virus-specific proteins in the plasma membrane of cells lytically infected or transformed by pol-oma virus.

Antisera, raised in rats, containing specificities directed against tumor antigen of polyoma virus also react with several proteins present in the plasma membrane of mouse cells infected with the virus. The main component has an apparent molecular weight of 55,000. The appearance of this protein after infection with early temperature-sensitive A mutants was temperature-dependent like tumor antigen itself. Pulse and chase isotope experiments suggest that this protein originates from a precursor, perhaps by cleavage; its production appears to be facilitated by the A mutation. Two other components with apparent molecular weights of 61,000 and 28,000 were also present but were more variable from experiment to experiment. All proteins were absent from the plasma membranes of cells infected with a transformation-defective mutant, NG-18. Up to four virus-specific proteins could be isolated from the plasma membranes of rat, hamster, and mouse cells transformed by the virus. The possible role of the plasma membrane proteins in cell transformation is discussed.

Membrane studies with polarity-dependent and excimer-forming fluorescent probes.

1. The interaction of electron-transporting particles from heavy mitochondria of ox heart with several fluorescent probes was examined. 2. 1-Anilinonaphthalene-8-sulphonate and 2-(N-methylanilino)naphthalene-6-sulphonate both show an energy-dependent response. 3. Energy transfer between the electron-transporting particles and the dyes and the kinetics of the dye-particle interaction were studied in order to locate the binding regions in the membrane. 4. The energy-dependent probe responses were shown to be a result of changes in the quantum yield of fluorescence of the bound dyes together with increased binding of the dyes to the energized membrane. 5. Fluorescence lifetime measurements were also used to observe changes on energization. 6. A new type of probe was found in pyrene-3-sulphonate, which may be regarded as a ;volume indicator' for the internal membrane binding region, since it shows a concentration-dependent excimer fluorescence. 7. By comparing the responses of all these dyes when energized particles are uncoupled, a membrane transition with a time-constant of 2-3s is inferred.