Kinetic characterization of ribonuclease S mutants containing photoisomerizable phenylazophenylalanine residues.

Incorporation of the photoisomerizable amino acid phenylazophenylalanine (PAP) into enzyme structures has been proposed as a strategy for photoswitching enzyme activity. To evaluate the strengths and limitations of this approach to enzyme photo-control, we performed a kinetic analysis of RNase S analogues containing PAP in positions 4, 7, 8, 10, 11 or 13. For an enzyme containing a single PAP group, the maximum extent of photoconversion (between approximately 96% trans/4% cis and 10% trans/90% cis under standard conditions) sets a limit on the maximum fold change in the initial rate of approximately 25-fold, if the cis form is the more active isomer, and approximately 10-fold if the trans form is more active. This extent of photoswitching was not realized in the present case because the effects of photoisomerization on kinetic constants were small and distributed among effects on S-peptide binding, substrate binding and the rate of the chemical step. These results suggest that photoisomerization could substantially alter enzyme kinetic constants but that a directed combinatorial approach might be required for realizing maximal photo-control in such systems. The limit set by the extent of photoconversion might be overcome by coupling multiple PAP groups to one enzyme or by altering the behaviour of a system that required oligomerization for activity.

Improving the performance of liquid-crystal-over-silicon spatial light modulators: issues and achievements.

The performance of liquid-crystal-over-silicon spatial light modulators has advanced rapidly in recent years. Most progress has centered around new device designs with increased bandwidth. In this paper we report on a number of techniques to improve the optical quality; these have applications in both current and future devices.

An immunohistological approach to persistent lymphadenopathy and its relevance to AIDS.

Recent evidence has shown that not only AIDS but also the majority of 'unexplained' persistent, generalized lymphadenopathy (PGL) are related to HTLV-III/LAV infections. The early detection how these changes may proceed to AIDS then become a prime interest. Eleven patients with PGL (10 homosexual males and one heterosexual haemophiliac) have been studied by immunohistology using monoclonal antibodies to dendritic reticulum cells of the germinal centre, T and B lymphocyte subsets, plasma cells and factor VIII, as an endothelial marker. In six cases only follicular and paracortical hyperplasia was detected, while in five other cases destruction of the dendritic reticulum cell network was seen with this sensitive method. This early destruction may explain the release of activated B cells into the circulation and prove to be an ominous prognostic sign, as it appears to correlate with 'prodromal' symptoms. In four out of 11 cases the depletion of T4+ cells in the paracortex was not as severe as in the blood, indicating that T4+ cells may preferentially settle in tissues at the time of T4 lymphopenia. In addition, germinal centres contained an additional patchy infiltration of T8+ cells. A patient with Kaposi's sarcoma did not show germinal centre destruction but did reveal extensive plasma cell infiltrates. Immunohistology may contribute to the definition of prognosis and analysis of disease progression in patients with PGL.

Isolation of Chlamydia trachomatis from the male urethra.

Chlamydia trachomatis was isolated from 26% of urethral swabs taken from 509 men with urethritis. The highest yield of 68% was obtained from a selected group of men with nonspecific urethritis (NSU) who had a frank urethral discharge. This is a higher than in previous reports, and is significantly higher than the isolation of C. trachomatis from men with less severe urethritis. The higher yield was similar to C. trachomatis isolation rates reported among patients with severe trachoma in hyperendemic areas. Men with a previous history of NSU had low isolation rates. Overall, 30% of 385 men with NSU had positive chlamydial culture results, 7% of 59 men with gonococcal urethritis alone were Chlamydia-positive, 15% of 59 men with gonorrhoea followed by NSU (post-gonococcal urethritis) were Chlamydia-positive, and only 3% of 61 men without urethritis harboured Chlamydia. Swabs taken from the cervical os of 28 of 108 female contacts of men with NSU had a positive result for C. trachomatis. Significantly more pairs of sexual partners had the same chlamydial culture result than had different results. The chlamydial isolation rate was higher among men admitting a casual sexual contact than in men claiming only regular partnerships. The findings provide further evidence for the sexual transmission of C. trachomatis and for its aetiological role in NSU.

Isolation of Chlamydia from women attending a clinic for sexually transmitted disease.

Cervical swabs for Chlamydia culture were collected from 638 unselected women attending a sexually transmitted diseases clinic with a fresh complaint. Chlamydia were isolated from 76 (12 per cent.) of the women. When the results were related to the patients' diagnoses, Chlamydia were present in 44 per cent. of women with gonorrhoea and in 22 per cent. of women who were contacts of men with nonspecific urethritis (women who may be regarded as having non-specific genital infection). Chlamydia were uncommon in women with no evidence of genital infection. Significant correlations were found between the presence of Chlamydia and cervical erosion, cervical cytological inflammatory change, and absence of symptoms. Isolates were obtained more frequently from women with non-specific genital infection who were primary contacts than from women who were secondary contacts. These findings support the concept that Chlamydia are pathogens in the genital tract and are sexually transmitted.