Fundus photocoagulation with the argon and krypton lasers: a comparative study

Photocoagulation of the monkey fundus with an argon-krypton laser photocoagulator was performed. Lesions produced by argon and krypton wavelengths were compared at various power settings, spot sizes, and exposure durations. At low energy levels argon laser lesions appeared clinically stronger than those produced by the krypton mode. Lesions in the foveal area produced with the argon laser demonstrated more extensive microscopic damage to the inner retinal layers than did those produced with the krypton laser. Histologically, both modalities affected the outer layers of the retina. However, the krypton wavelength affected more of the choriocapillaries and the larger choroidal vessels than the argon wavelengths. Conversely, argon laser coagulation of the retinal vessels damaged the perivascular tissue in the nerve fiber layer more than the krypton laser did. Rupture of Bruch's membrane and choroidal hemorrhage occurred frequently with the krypton laser at low energy levels when a small spot size and a short coagulation time were used. Both complications were less likely to occur with argon burns at similar dosage parameters. By choosing larger spot sizes and longer coagulation times for the krypton laser, these complications were prevented.

Codon recognition rules in yeast mitochondria

The mitochondrial genome of Saccharomyces cerevisiae codes for 24 tRNAs. The nucleotide sequences of the tRNA genes suggest a unique set of rules that govern the decoding of the mitochondrial genetic code. The four codons of unmixed fmilies are recognized by single tRNAs that always have a U in the wobble position of the anticodon. The codons of the mixed families are read by two different tRNAs. Codons terminating in a C or U are recognized by tRNAs with a G and codons terminating in a G or A are recognized by tRNAs with a U in the corresponding positions of the anticodons. There are two exceptions to these rules. In the AUN family for isoleucine and methionine, the isoleucine tRNA has a G and the methionine tRNA has a C in the wobble position. The tRNA for the arginine CGN family also has an A in the wobble position of the anticodon. It is of interest that the CGN codons have not been found in the mitochondrial genes sequenced to date. The simplified decoding system of yeast mitochondria allows all the codons to be recognized by only 24 tRNAs.

Assembly of the mitochondrial membrane system: sequences of yeast mitochondrial valine and an unusual threonine tRNA gene

The mitochondrial DNA segments of two independently isolated rho- clones of S. cerevisiae carrying a genetic marker for a threonine tRNA have been characterized by restriction endonuclease analysis and DNA sequencing. The DNA sequences of the two segments have been used to deduce the primary and secondary structures of the tRNA. The threonine tRNA is unusual in having a leucine anticodon (3'-GAU-5'). Despite the anomalous anticodon, the tRNA is proposed to function in mitochondrial protein synthesis. One of the rho- clones contains an additional coding sequence that has been identified as a valine tRNA genes have been located on the wild-type physical map and determined to be transcribed from two different strands.

Use of the UGA terminator as a tryptophan codon in yeast mitochondria

We propose that the UGA terminator regularly occurs as a tryptophan codon in yeast mitochondrial DNA. This conclusion is based on the sequence analysis of mitochondrial DNA regions coding for structural genes of cytochrome b, cytochrome oxidase, and the ATPase.

Formation of carcinogenic N-nitroso compounds in corn-bread inoculated with fungi

DMNA, DENA and MBNA are formed in corn-bread which has been inoculated with the most common species of fungi found in foodstuffs of Lin Xian County, Henan Province, such as F. moniliforme, A. flavus and others, and then, added with small amount of NaNO2 after a few days of incubation. These carcinogenic N-nitroso compounds can induce cancer of the liver or/and esophagus in experimental animals. Results of the present study show the capability of some fungi to produce chemical carcinogens as well as mycotoxins in contaminated food, and thus, open a new field of research in cancer etiology.

The effect of alpha-1-acetylmethadol hydrochloride on rat hepatic aryl hydrocarbon hydroxylase and epoxide hydrase

Male and female Wistar rats were administered alpha-1-acetylmethadol via their drinking water for one to two weeks. Hepatic aryl hydrocarbon hydroxylase, cytochrome P-450 and epoxide hydrase activities were measured after various doses of this drug. In female rats, a significant increase in aryl hydrocarbon hydroxylase and cytochrome P-450 occurred at doses as low as 4.7 mg/Kg/day. However, no change in epoxide hydrase activity occurred. In male rats, a significant increase in epoxide hydrase activity occurred at all doses tested. From these results, it is concluded that alpha-1-acetylmethadol induces a number of hepatic drug metabolizing enzyme systems.