The mass photoreceptor response of the isolated carp retina was studied after immersing the tissue in aspartate-Ringer solution. Two electro-retinogram components were isolated by differential depth recording: a fast cornea-negative wave, arising in the receptor layer, and a slow, cornea-negative wave arising at some level proximal to the photoreceptors. Only the fast component was investigated further. In complete dark adaptation, its action spectrum peaked near 540 nm and indicated input from both porphyropsin-containing rods (lambda(max) approximately 525 nm) and cones with longer wavelength sensitivity. Under photopic conditions a broad action spectrum, lambda(max) approximately 580 nm was seen. In the presence of chromatic backgrounds, the photopic curve could be fractionated into three components whose action spectra agreed reasonably well with the spectral characteristics of blue, green, and red cone pigments of the goldfish. In parallel studies, the carp rod pigment was studied in situ by transmission densitometry. The reduction in optical density after a full bleach averaged 0.28 at its lambda(max) 525 nm. In the isolated retina no regeneration of rod pigment occurred within 2 h after bleaching. The bleaching power of background fields used in adaptation experiments was determined directly. Both rods and cones generated increment threshold functions with slopes of +1 on log-log coordinates over a 3-4 log range of background intensities. Background fields which bleached less than 0.5% rod pigment nevertheless diminished photoreceptor sensitivity. The degree and rate of recovery of receptor sensitivity after exposure to a background field was a function of the total flux (I x t) of the field. Rod saturation, i.e. the abolition of rod voltages, occurred after approximately 12% of rod pigment was bleached. In light-adapted retinas bathed in normal Ringer solution, a small test flash elicited a larger response in the presence of an annular background field than when it fell upon a dark retina. The enhancement was not observed in aspartate-treated retinas.

Adaptation, Ocular↗

PubMed1973

Localization and characterization of the hippuricase activity of group B streptococci.

Studies are presented on the isolation, localization, and characterization of hippuricase activity of group B streptococci. Washed, intact cells, live or heat killed at 56 C, exhibited hydrolysis of hippuric acid, but cell-free filtrates of the organism did not. Excellent hippuricase activity was recoverable from supernatant fluids of mechanically disrupted cells, and evidence suggests that it exists largely intracellularly. Characteristics of the hippuricase preparation are consistent with the view that the biologically active principle is an enzyme. A quantitative microtiter technique has been developed which is useful in titrating enzymatic activity and antibody neutralization. Sera from rabbits immunized with filtered preparations neutralized hippuricase activity.

Amidohydrolases↗

PubMed1973