Search PubMed⌕ Search

Biomedical subjects

O Marin

Publications and source records attributed to O Marin.

80 records · Page 5Linked to original sources
PubMed1989

A synthetic peptide substrate specific for casein kinase I.

The synthetic peptide, Asp-Asp-Asp-Glu-Glu-Ser-Ile-Thr-Arg-Arg, derived from the phosphorylation site of casein kinase-1 (CK-1) in beta-casein A(2), is readily phosphorylated by CK-1, but not by casein kinase-2(CK-2), cyclic AMP-dependent protein kinase, protein kinase C, phosphorylase kinase and protein kinase FA. Phosphorylation by CK-1 occurs only at Ser-6, Thr-8 being unaffected. The Km for the peptide is higher (1 mM) than for beta-casein A(2) (40 microM), while the Vmax is quite comparable. This is the first synthetic peptide substrate for CK-1 described so far, and can be used for the rapid and specific estimation of CK-1 activity in crude extracts.

Amino Acid Sequence↗
PubMed1989

Visual, vestibular and somatosensory contributions to balance control in the older adult.

Age- and pathology-related changes in the relative contributions of visual and somatosensory inputs to dynamic balance control were evaluated. Young adults (mean age = 25, SD = 4) were compared to older adults (mean age = 68, SD = 5). Electromyographic responses were collected when subjects' balance was perturbed on a movable platform. The amounts of visual information and of somatosensory input at the ankle were manipulated. Muscle response latencies, losses of balance, and muscle sequencing were analyzed. Muscle response latencies did not differ across age groups. Loss of balance data indicated that older adults were less stable under conditions in which peripheral vision was occluded and ankle somatosensation was limited (only foveal vision and vestibular input remaining). Older adults showed more antagonist muscle activation and used muscle sequences not seen in young adults (e.g., hip strategy). These effects were exaggerated among subjects in whom borderline pathology had been diagnosed.

Accidental Falls↗
PubMed1988

Synthetic peptide substrates for casein kinase 2. Assessment of minimum structural requirements for phosphorylation.

Unlike the peptides SAEAAA and SEEAAA which are not substrates for casein kinase 2 (CK-2) their analogs SAAEAE and SAAEAA are still significantly phosphorylated. Their Km values, however, (13.3 and 18.9 mM, respectively) are almost two orders of magnitude higher than that of SEEEEE and their Vmax values are 3- and 14-fold lower than that of SAAEEE. The peptide ESEEEEE, but not ASEEEEE, is a slightly better substrate than SEEEEE, while both RSEEEEE and SEEEKE are very poor substrates compared to ASEEEEE and SEEEAE, respectively. SAAEAE is much more responsive to polylysine stimulation and polyphosphate inhibition than is SEEEEE. Taken together these data show that a single acidic residue at the third position from the C-terminal side of the phosphorylatable amino acid represents not only a necessary, but also a sufficient condition for site recognition by CK-2. Optimal phosphorylation efficiency, however, requires an extended C-terminal cluster of several acidic residues, and can be compromised by the presence of only a basic residue either inside the acidic cluster or adjacent to the N-terminal side of the phosphoacceptor amino acid. The structure of the phosphoacceptor site can greatly influence the efficacy of substrate-directed effectors of CK-2.

Amino Acid Sequence↗
PubMed1987

Ca2+ phospholipid-dependent and independent phosphorylation of synthetic peptide substrates by protein kinase C.

Several synthetic peptides reproducing fragments of protamines have been used as model substrates for Ca2+/phospholipid-dependent protein kinase C, tested both in the absence of any effector (basal conditions) and upon activation by either Ca2+ and phosphatidylserine (or diacylglycerol) or limited proteolysis. Only the peptide Arg4-Tyr-Gly-Ser-Arg6-Tyr [Ga(52-65)] shares the unique property of protamines of being readily phosphorylated even under basal conditions. Optimal activity in the absence of effectors is observed with Tris/HCl buffer pH 7.5; Pipes and Hepes are less effective at pH 7.5, and at pH 6.5 basal phosphorylation is reduced. Under the best conditions for basal phosphorylation of Ga(52-65), its derivative with ornithine replaced for arginine and those corresponding to its C-terminal fragments Gly-Ser-Arg6-Tyr [Ga(57-65)] and Gly-Ser-Arg3 [Ga(57-61)], as well as the peptides Pro-Arg5-Ser2-Arg-Pro-Val-Arg [Th(1-12)], Arg4-Tyr-Arg2-Ser-Thr-Val-Ala [Th(13-23)] and Arg2-Leu-Ser2-Leu-Arg-Ala are not significantly affected though all of them, like histones, are more or less readily phosphorylated upon activation of protein kinase C by Ca2+/phosphatidylserine. The peptide Ser2-Arg-Pro-Val-Arg [Th(7-12)] however, corresponding to the C-terminal part of Th(1-12), is not phosphorylated even in the presence of activators. Limited proteolysis can roughly mimic the Ca2+/phosphatidylserine effect inducing however different extents of activation depending on the nature of the peptide substrates. Our results support the following two conclusions. Basal phosphorylation by protein kinase C in the absence of any effector requires peptide substrates whose target residue(s) are included between two extended arginyl blocks and is also dependent on pH and nature of the buffer. Peptides having extended clusters of either arginyl or ornithyl residues on the C-terminal side of serine are also readily phosphorylated, but they need activation of protein kinase by either Ca2+/phosphatidylserine or limited proteolysis. The same is true of peptides having basic residues only on the N-terminal side, or even on both sides but in limited number.

Amino Acid Sequence↗
PubMed1986

Site specificity of casein kinase-2 (TS) from rat liver cytosol. A study with model peptide substrates.

The factors determining the site recognition and phosphorylation by rat liver casein kinase-2 (CK-2) have been explored with a set of 14 related hexapeptides each including a single phosphorylatable amino acid and five acidic plus neutral residues. Such peptides are different from each other in the following features: the nature of the phosphorylatable amino acid, if any; its position relative to the critically required acidic residues; the extension and the structure of the acidic cluster. All of them were tested as substrate and/or competitive inhibitors of CK-2, and their kinetic and inhibition constants were determined. The results suggest the following conclusions. Under strictly comparable conditions Ser is by far preferred over Thr. Tyr not being affected at all. In order to carry out its role of structural determinant the critical acidic cluster must be located on the C-terminal side of the target residue, though not necessarily adjacent to it. The affinity for the protein-binding site, as deduced from Km and/or Ki values, is largely dependent on the number of acidic residues but it is also significantly enhanced if a hydroxylic residue is located on their N-terminal side. An acidic residue at position +3 relative to serine plays an especially important role for triggering phosphorylation, the peptide Ser-Glu-Glu-Ala-Glu-Glu having similar Km but negligible Vmax compared to Ser-Glu-Ala-Glu-Glu-Glu and Ser-Glu-Glu-Glu-Ala-Glu. These data provide a rationale for the substrate specificity of CK-2 and will give a helpful insight into the structure of the protein-binding site of this enzyme.

Amino Acids↗
PubMed1983

Stance posture control in select groups of children with cerebral palsy: deficits in sensory organization and muscular coordination.

This study has focused upon the automatic components of posture and movement in a group of ten cerebral palsy children carefully selected to represent a spectrum of abnormalities relatively pure by clinical standards and ten age-matched normals. Each subject stood unsupported upon a movable platform and within a movable visual surround and was then exposed to external perturbations or was asked to pull with one arm upon a movable handle. In comparing the performance of cerebral palsy children in each clinical category with the age-matched normals and with normal adults assessed in previous studies, the process of maintaining stance was subdivided into two component functions: substrates which determined the onset timing, direction and amplitude of postural actions from somatosensory, vestibular, and visual stimuli were termed "sensory organization", and those establishing temporal and spatial patterns of muscular contractions appropriate to produce effective movements were termed "muscle coordination". We found among seven of the ten cerebral palsy children a clear localization of dysfunction within either sensory organization or muscle coordination mechanisms. These results are providing some new insights into the organization of each of these processes as well as suggesting methods for developing a more systematic understanding of the abnormalities of movement control.

Cerebral Palsy↗
PubMedDate not supplied

[The main aspects of vesical risk in intraperitoneal surgery].

They are described the main aspects of vezical risk in intraperitoneal surgery: subembilical celiostomy, haernios surgery, rectal surgery, gynecological surgery. It is shown few aspects of our experience in the treatment of haernias, vesicovaginal fistules secondary to total hysterectomy.

Carcinoma↗