Melanocortin‐1 receptor structure and functional regulation

The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light.     

A general,fast, and sensitive micromethod for DNA determination: Application to rat and mouse liver,rat hepatoma,human leukocytes,chicken fibroblasts,and yeast cells

A fluorometric method using 3,5-diaminobenzoic acid for DNA determination in tissues, cultured cells, nucleated blood cells, and yeast cells is described. The method is general, simple, and rapid, and does not require prior DNA extraction, since tissue is directly solubilized in Triton X-100 and ammonia. The procedure is highly sensitive, and is able to measure rather accurately as little as 10 ng of DNA. It is applicable to all types of DNA structure. The DNA content determined in various tissues and cells was: 2.50 mg/g fresh rat liver, 3.32 mg/g rat diethylnitrosamine-induced hepatoma, 2.49 mg/g fresh mouse liver, 8.76 μg/10⁶ human leukocytes, 3.37 μg/10⁶ chicken fibroblasts, 2.97 μg/10⁸ haploid yeast cells, and 2.84 μg/10⁸ haploid yeast protoplasts.     

A computer algorithm to determine the recognition site of restriction enzymes

A new algorithm is proposed to determine the type-II restrictionendonucleases' recognition site knowing the digested DNA sequenceand fragment lengths in an actual case. The algorithm is implementedfor the Commodore 64 microcomputer. Received on January 6, 1987; accepted on June 19, 1987     

How the Visual Cortex Handles Stimulus Noise: Insights from Amblyopia

Adding noise to a visual image makes object recognition more effortful and has a widespread effect on human electrophysiological responses. However, visual cortical processes directly involved in handling the stimulus noise have yet to be identified and dissociated from the modulation of the neural responses due to the deteriorated structural information and increased stimulus uncertainty in the case of noisy images. Here we show that the impairment of face gender categorization performance in the case of noisy images in amblyopic patients correlates with amblyopic deficits measured in the noise-induced modulation of the P1/P2 components of single-trial event-related potentials (ERP). On the other hand, the N170 ERP component is similarly affected by the presence of noise in the two eyes and its modulation does not predict the behavioral deficit. These results have revealed that the efficient processing of noisy images depends on the engagement of additional processing resources both at the early, feature-specific as well as later, object-level stages of visual cortical processing reflected in the P1 and P2 ERP components, respectively. Our findings also suggest that noise-induced modulation of the N170 component might reflect diminished face-selective neuronal responses to face images with deteriorated structural information.     

ATP stimulates inositol phosphates accumulation and calcium mobilization in a primary culture of rat aortic myocytes

The effects of extracellular ATP on phosphoinositide metabolism and intracellular Ca2+ concentration were studied in a primary culture of rat aortic myocytes. ATP increases the level of inositol phosphates, the putative second messenger for Ca2+ mobilization. No saturation of inositol phosphates accumulation is obtained (up to 10(-2) M ATP). Under the same conditions, ATP rapidly mobilizes intracellular Ca2+ in fura-2 loaded myocytes. The mobilization of intracellular Ca2+ is dose-dependent (maximal at 10(-4) M ATP), and is not affected by addition of EGTA. It is concluded that the receptors mediating the cytosolic increase of Ca2+ are of the P2-purinoceptor subtype. The physiological functions of these receptors are not presently known.     

Neurochemical evidence for two types of presynaptic alpha2-adrenoceptors

Neurochemical and pharmacological evidence has been obtained that noradrenergic varicosities (in mouse and rat vas deferens) and cholinergic varicosities (in the Auerbach's plexus) contain heterogenous alpha₂-adrenoceptors through which the release of [³H]noradrenaline and [³H]acetylcholine can be modulated. The quantitative data also support the hypothesis that different noradrenaline and xylazine sensitive alpha₂-adrenoceptors are present prejunctionally in the vas deferens and Auerbach's plexus preparations. Prazosin, although it has a presynaptic inhibitory effect on alpha₂-adrenoceptors of noradrenergic axon terminals, has no effect on cholinergic axon terminals. These data suggest that there are two different types of alpha₂-adrenoceptors at the presynaptic axon terminals.Special Issue Dedicated to Dr. Abel Lajtha     

Penicillin-binding proteins of protoplast and sporoplast membranes of Streptomyces griseus strains

Membrane-bound penicillin-binding proteins (PBPs) of two Streptomyces griseus strains that sporulate well in liquid and solid medium have been investigated during the course of their life-cycle. The PBP patterns were analyzed by sodium dodecylsulphate polyacrylamide-gel electrophoresis and fluorography. One strain (No. 45 H) has only a single band (mol wt: 27,000) in early log phase, and two additional PBPs of higher mol wt (69,000 and 80,000) in the late log phase. The other strain (No. 2682) possessed two bands with mol wts 27,000 and 38,000 which did not change during its vegetative phase. In strain No. 2682, a new PBP with a mol wt of 58,000 appeared in spore membranes while one of those (mol wt 38,000) present in mycelial membranes disappeared. Our results suggest that appearance of the new PBP in the spore may be associated with the sporulation process. The major PBP band (mol wt: 27,000) present in all stages of the life cycle of these strains, may be characteristic of S. griseus while the other PBPs reflect certain stages of the life cycle. A new method was developed for the production of spore protoplasts by consecutive enzymatic treatments.Abbreviation PBP penicillin-binding protein     

The receptor for human sex steroid binding protein (SBP) is expressed on membranes of neoplastic endometrium.

Sex steroid binding protein (SBP) receptor was detected on cell membranes obtained from human endometrium adenocarcinoma. The binding of SBP was proved to be highly specific, saturable, and at high affinity. It was, additionally, shown to occur at two sites at different affinities, as previously described for other human tissues. SBP was, therefore, demonstrated to recognized a specific receptor on endometrium adenocarcinoma membranes. The effect of steroid hormones on SBP-receptor interaction was also evaluated. Both dihydrotestosterone and estradiol were shown to inhibit the binding of SBP to its specific receptor on neoplastic membranes. Testosterone at a dose of 10(-9) M was shown not to interfere to a significant extent with SBP-receptor binding. The sensitivity for estradiol we had previously observed in normal premenopausal endometrium was completely lost in postmenopausal neoplastic tissue. These observations suggest that the SBP-membrane recognition system is still present in neoplastic postmenopausal endometrium, but it has been modified either by the postmenopausal endogenous milieu or by the neoplastic transformation.