[Evaluation of the electrode position by CBCT following cochlear implantation]

Objective: To observe the position of the electrode in the cochlea following cochlear implantation by cone beam computed tomography (CBCT). Methods: Twenty-five children who received cochlear implantation and CBCT examinations in the Department of Otorhinolaryngology Head and Neck Surgery from the Second Hospital of Shandong University between January 2016 and December 2017 were selected. There were 15 males (17 ears) and 10 females (10 ears). The age ranged from 0.5 to 7.0 years old, with a median age of 1.6 years. 23 patients with unilateral implantation and two patients with bilateral implantation. The implants were all Med-El standard 12-electrode contact arrays. The CBCT was used to determine the position of the electrode in the cochlea, the distance between the electrode contacts and modiolus, and intracochlear insertion length of the electrode arrays. SPSS Statistics, version 22.0 was used for data processing and statistical analysis. Results: CBCT images could clearly demonstrate the structure of round window, oval window, modiolus, osseous cochlear duct, osseous spiral lamina, and electrodes. The electrode arrays of all the children were fully implanted into the cochlea. 26 of the electrode arrays were located in the scala tympani and one of them was inserted into the scala vestibular. The mean intracochlear insertion length of the electrode arrays was 30.23 (95%CI, 30.04-30.71) mm. The distance between the electrode contacts and modiolus gradually increased at the 1-4th electrode contacts and reached the maximum at the 4th electrode contacts with an average of 1.10 mm (95%CI, 1.02 to 1.18 mm), and then gradually decreased from the 5th electrode contacts. Conclusions: CBCT can clearly show cochlear fine structures and therefore accurately assess the electrode position following cochlear implantation.

Creatine kinase: the characteristics of the enzyme regenerated from the thio-methylated creatine kinase reflect a differentiation in function between the two reactive thiols

The activity of S-thiomethyl-modified creatine kinase is due to regeneration of the free thiol (Hou and Vollmer, Biochim Biophys Acta (1994) 1205, 83-88). Characteristics of enzyme regenerated from the S-thiomethyl-modified creatine kinase are reported in the present study. The intrinsic fluorescence of the regenerated enzyme is similar to that of the native enzyme in the presence or absence of the dead-end complex. Regenerated CK (rCK) with full activity has only one reactive thiol. The rate constant of the rCK-reactive thiol reacting with DTNB is close to that of the slow phase of the reactive thiols of the native enzyme. If the IAM-modified rCK is treated with the same method as that for obtaining the rCK, the thiol-methylated reactive thiol of the rCK is reduced to a free SH and a regenerated enzyme, RCK, is produced with about 10% of the rCK activity. Therefore, the different roles of the two reactive thiols of creatine kinase may stem from the characteristics of the rCK, which suggests that only one of the two reactive thiols is related to the activity of the enzyme and the slower phase thiol (the first SH) in the modification reaction with DTNB is directly related to the enzymatic activity, while the faster phase thiol (the second SH) assists the first SH. This compensatory mechanism is proposed in the present study to interpret the dispute on the reactive SH role in the enzymatic catalysis.

The activity of S-thiomethyl modified creatine kinase is due to the regeneration of free thiol at the active site

Creatine kinase modified by S-methyl methanethiosulfonate and devoid of reactive thiol group has been reported to retain about 18-40% of the activity of the native enzyme. It has now been found that during the reaction catalyzed by the modified enzyme the rate increases with time and if the reaction is allowed to continue sufficiently long, the enzyme eventually recovers full activity. The presence of substrates is not required for the reactivation as suitable dilution after removal of MMTS in excess leads to complete reactivation of the MMTS modified enzyme with the simultaneous regeneration of reactive thiol per each dimeric molecule as shown by determinations with DTNB and IAN. The addition of MMTS during the course of reactivation again inactivates the reactivated enzyme. The activity recovery is therefore due to the regeneration of reactive thiol and it appears that the active-site thiols are essential for the activity of rabbit muscle creatine kinase.

Increased thermal stability of proteins in the presence of naturally occurring osmolytes

Organisms and cellular systems which have adapted to stresses such as high temperature, desiccation, and urea-concentrating environments have responded by concentrating particular organic solutes known as osmolytes. These osmolytes are believed to confer protection to enzyme and other macromolecular systems against such denaturing stresses. Differential scanning calorimetric (DSC) experiments were performed on ribonuclease A and hen egg white lysozyme in the presence of varying concentrations of the osmolytes glycine, sarcosine, N,N-dimethylglycine, and betaine. Solutions containing up to several molar concentrations of these solutes were found to result in considerable increases in the thermal unfolding transition temperature (Tm) for these proteins. DSC scans of ribonuclease A in the presence of up to 8.2 M sarcosine resulted in reversible two-state unfolding transitions with Tm increases of up to 22 degrees C and unfolding enthalpy changes which were independent of Tm. On the basis of the thermodynamic parameters observed, 8.2 M sarcosine results in a stabilization free energy increase of 7.2 kcal/mol for ribonuclease A at 65 degrees C. This translates into more than a 45,000-fold increase in stability of the native form of ribonuclease A over that in the absence of sarcosine at this temperature. Catalytic activity measurements in the presence of 4 M sarcosine give kcat and Km values that are largely unchanged from those in the absence of sarcosine. DSC of lysozyme unfolding in the presence of these osmolytes also results in Tm increases of up to 23 degrees C; however, significant irreversibly occurs with this protein.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of denaturation and inactivation rates of creatine kinase in guanidine solutions

Both the denaturation, as followed by UV absorbance and fluorescence changes, and inactivation of creatine kinase in guanidine solutions have been found to be first order reactions. In 3 M guanidine, at 30 degrees C, the inactivation rate constant was found to be 5.9 sec-1 and the denaturation rate constant 1.9 sec-1. At lower guanidine concentrations, the inactivation rate constants were only little affected whereas the denaturation rate constants decreased markedly, being of the order of 0.04 in 1 M and 0.004 in 0.5 M guanidine. The kinetics of the inactivation reaction in 0.5 M guanidine was found to be in agreement with a combination of two first order reactions. The enzyme lost activity first by a fast reaction with a rate constant only slightly lower than the rate constant in 3 M guanidine followed by a slower reaction with a rate constant of 0.003 sec-1. In 0.3 M guanidine, very little change in either UV absorbance or in fluorescence was observed, but, in sharp contrast, the enzyme lost considerable activity by a fast reaction and this was followed by a slower reaction of inactivation. Even after prolonged denaturation in 0.5 and 0.3 M guanidine, residual activities of 3.4% and 30% remained respectively. The above results suggest a very fragile active site although dissociation of the dimer and reversible guanidine inhibition may also contribute to the initial rapid inactivation. It is also to be noted that the multiphasic courses of inactivation at lower guanidine concentrations seem to suggest the presence of partly active intermediates during denaturation.

Conformational changes of creatine kinase during guanidine denaturation

The conformational changes of creatine kinase during denaturation by different concentrations of guanidine hydrochloride have been studied by fluorescence and ultraviolet difference spectroscopic methods. At low concentrations of guanidine, less than 1 M, the denatured minus native difference spectra showed two negative peaks at 281 and 287 nm, whereas the fluorescence emission increased markedly with its maximum red-shifted from 337 to 345 nm. Control experiments showed that guanidine also increased the emission of ionized tyrosine at 345 nm. With the increase of concentrations of guanidine, both negative peaks at 281 and 287 nm increased in magnitude to reach maximal values at 3 M guanidine and at this time a small peak appeared at 292 nm. The fluorescence maximum was further red-shifted to 355 nm, whereas the emission intensity of the main peak decreased and a small shoulder appeared at 310 nm when the guanidine concentration increased from 1 to 3 M. Further increase in guanidine concentration produced little further change either in UV absorption or in fluorescence. From the above results, it seems that, in the native enzyme. Trp residues are partly buried and partly exposed and some of the Tyr residues are in ionized state. Guanidine below 1 M does not expose the buried Trp residues nor affects significantly the microenvironments of the ionized Tyr residues. At 3 M guanidine, Trp residues are exposed and the ionization state of Tyr residues is also affected. At this concentration, the peptide chain seems to be fully unfolded as evidenced by the fact that 5 M guanidine produces little further change in both UV absorption and fluorescence.