Lactate dehydrogenase in developing rat oral epithelium

Freeze-dried sagittal, whole-body sections of 10-day-old rats were incubated for lactic dehydrogenase (LDH) using different media in the presence of the inhibitors urea and fluoropyruvate. Phenazine methosulfate (PMS) and menadione, which are regularly used in current histochemical media and are believed to promote the demonstration of LDH activity, were also added and shown to be insufficient for the demonstration of total LDH activity, and PMS even seemed to have an inhibitory effect on LDH activity in oral epithelium. However, cumulated data from the different incubations show that the oral epithelium of developing rats may contain two different types of LDH, one in the basal cells with possibly aerobic characteristics, and another in the spinosum/granulosum cells with anaerobic characteristics.     

Selective alkylation of G24 residue in tRNAPhe

Alkylation of E. coli tRNAPhe with 4-(N-2-chloroethyl-N-methylamino) benzyl-5'-phosphamide of oligonucleotide d(pAACCA) was studied. G24 residue located near the sequence C17GGDA21 partially complementary to the oligonucleotide moiety of the reagent was shown to be alkylated. Oligonucleotide d(pAACCA) inhibited the alkylation. Association constant of oligonucleotide derivative with tRNAPhe (10(3) M-1) was evaluated from the dependence of the extent of tRNA modification on the concentration of the reagent. The reported method for selective alkylation of tRNA may be used for preparing photoaffinity derivatives of tRNA bearing an arylazidogroups in desired position.     

Distribution of amino acid residues in the primary protein structure

The amino acid composition and sequence in primary structure of 180 proteins have been studied. It is shown that the distribution of amino acid residues is near to a random one, i.e. it is determined by the amino acid composition. The ratio between statistical and unique character of protein primary structures has been discussed. The amino acid sequence is suggested to be unique in fibrous proteins. In contrast the amino acid sequence in globular proteins is a statistical one. The statistical character of amino acids distribution in globular proteins explains the possibility of sensible text generation under the frame shift mutations, deletions and insertions.     

An estimate on the effect of point mutation and natural selection on the rate of amino acid replacement in proteins

We outline a method for estimating quantitatively the influence of point mutations and selection on the frequencies of codons and amino acids. We show how the mutation rate, i.e., the rate of amino acid replacement due to point mutation, can be affected by the codon usage as well as by the rates of the involved base exchanges. A comparison of the mutation rates calculated from reliable values of codon usage and base exchange probabilities with those that would be expected on the basis of chance reveals a notable suppression of replacements leading to tryptophan, glutamate, lysine, and methionine, and particularly of those leading to the termination codons. If selection constraints are neglected and only mutations are taken into account, the best agreement between expected and observed frequencies of both codons and amino acids is obtained for alpha = 1.13-1.15, where (Formula: see text). The "selection values" of codons and amino acids derived by our method show a pattern that partially deviates from others in the literature. For example, the selection pressure on methionine and cysteine turns out to be much more pronounced than expected if only the discrepancies between their observed and expected occurrences in proteins are considered. To estimate to what extent randomly occurring amino acid replacements are accepted by selection, we constructed an "acceptability matrix" from the well-established matrix of accepted point mutations. On the basis of this matrix "acceptability values" of the amino acids can be defined that correlate with their selection values. We also examine the significance of mutations and selection of amino acids with respect to their physicochemical properties and functions in proteins. The conservatism of amino acid replacements with respect to certain properties such as polarity can be brought about by the mutational process alone, whereas the conservatism with respect to other relevant properties--among them all measures of bulkiness--obviously is the result of additional selectional constraints on the evolution of protein structures.     

The sup8 tRNALeu gene of Schizosaccharomyces pombe has an unusual intervening sequence and reduced pairing in the anticodon stem

Summary We have cloned and sequenced the wild-type and suppressor alleles of the S. pombe sup8 tRNA gene. The wild-type allele has a leucine UAA anticodon and the suppressor (sup8-e) carries the opal suppressor anticodon UCA. The gene has a 16 base pair intervening sequence that, in the RNA, is predicted to form a secondary structure which involves base pairing to the 5, rather than the usual 3 side of the 5 splice site. When incubated in Saccharomyces cerevisiae cell-free extracts both alleles are efficiently transcribed, the 5 leader and 3 trailer sequences are removed and CCA is added to the 3 processed end; however, the intervening sequence is not excised. This finding implies that the structural requirements of the splicing endonucleases in the two yeasts have diverged. No other tRNA genes with related sequences were detected in S. pombe DNA by hybridization, suggesting that other UUA isoacceptors may be structurally dissimilar to sup8 or that the UUA codon may be decoded by a UUG leucine isoacceptor.     

Phytosociological characteristics of theRondeletio correifoliae-Andropogonetum multinervosi ass. nova (Sierra de la Siguanea,Isla de la Juventud,Cuba)

The contribution deals with the phytocenological analysis of theRondeletio correifoliae-Andropogonetum multinervosi, an endemic savanna association occuring on the Siguanea Hills (Sierra de la Siguanea) near the Colony Hotel.     

The Electrical Conductivity of Bovine Milk in Mastitis Diagnosis

The electrical conductivity (EC) of milk is mainly a function of the electrolyte concentration in the milk and therefore raised in mastitis. The present investigation was aimed at elaborating, if possible, a diagnostic model for screening purposes based on EC determinations and consistent with the diagnostic procedures and interpretations commonly used in laboratory milk diagnosis in the Nordic countries (Klastrup 1975). According to this diagnosis (here called reference diagnosis) cell numbers above 300,000/ml (cell count or the corresponding CMT-score) in foremilk quarter samples during the main part of the lactation period and significantly above the lowest value on within-udder comparison during late lactation are considered indicative of mastitis and bacteriological examinations are made when called for.