Previous work has shown that phonetic difficulty affects older, but not younger, speakers who stutter and that older speakers experience more difficulty on content words than function words. The relationship between stuttering rate and a recently-developed index of phonetic complexity (IPC, Jakielski) was examined in this study separately for function and content words for speakers in 6-11, 11 plus-18 and 18 plus age groups. The hypothesis that stuttering rate on the content words of older speakers, but not younger speakers, would be related to the IPC score was supported. It is argued that the similarity between results using the IPC scores with a previous analysis that looked at late emerging consonants, consonant strings and multiple syllables (also conducted on function and content words separately), validates the former instrument. In further analyses, the factors that are most likely to lead to stuttering in English and their order of importance were established. The order found was consonant by manner, consonant by place, word length and contiguous consonant clusters. As the effects of phonetic difficulty are evident in teenage and adulthood, at least some of the factors may have an acquired influence on stuttering (rather than an innate universal basis, as the theory behind Jakielski's work suggests). This may be established in future work by doing cross-linguistic comparisons to see which factors operate universally. Disfluency on function words in early childhood appears to be responsive to factors other than phonetic complexity.
Tissue culture substratum adhesion sites from EGTA-detached Platt human neuroblastoma cells were extracted with a buffer containing ocytlglucoside, NaCl, guanidine hydrochloride, and a variety of protease inhibitors, an extraction which resulted in quantitative solubilization of the 35SO4 = -radiolabeled proteoglycans and 3H-leucine-radiolabeled proteins. Of the sulfate-radiolabeled material, the vast majority was heparan sulfate proteoglycan (Kav = 0.15 on Sepharose C14B columns) and the remainder was chondroitin sulfate chains (no single chains of heparan sulfate were observed). This extract was then fractionated on DEAE-Sephadex columns under two different buffer elution conditions. Under DEAE-I conditions in low ionic strength acetate buffer, two major peaks of 35SO4 = -radiolabeled material (A,B) and a minor peak (C) could be resolved in the NaCl gradient; however, three-fourths of the material required 4 M guanidine hydrochloride to elute it from the column (peak D). Under DEAE-II conditions in acetate buffer supplemented with 8 M urea, the vast majority of the proteoglycan material could be eluted in the NaCl gradient as peak AB. Peak D material was shown to contain aggregated proteoglycan, along with nonproteoglycan protein, which high concentrations of urea or guanidine could dissociate, but not nonionic or zwitterionic detergents. Three different affinity chromatography systems were used to further characterize these components. Approximately 60% of peak A heparan sulfate proteoglycan from DEAE-I binds to the hydrophobic matrix, octyl-Sepharose, while 80% of the proteoglycan in DEAE-I peak D binds to this hydrophobic column. A sizable fraction of peak A proteoglycan fails to bind to plasma fibronectin but does bind to platelet factor-4 affinity columns. In contrast, peak AB proteoglycan from DEAE-II columns yields a much higher proportion of molecules which do bind to fibronectin. To examine the basis for these differences in affinity binding, nonproteoglycan protein from these adhesion sites was mixed with peak AB proteoglycan prior to affinity chromatography; proteoglycan binding to fibronectin decreased markedly while binding to platelet factor-4 was unaffected. This modulating activity involves the binding of nonproteoglycan protein in adhesion site extracts to both fibronectin on the column, as well as to heparan sulfate proteoglycan itself, and it could not be mimicked by a number of known proteins in adhesion site extracts or several other proteins. These results demonstrate selectivity and specificity in this modulation and indicate that a previously unidentified protein(s) is responsible.(ABSTRACT TRUNCATED AT 400 WORDS)
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