ABSTRACT
To understand the structural properties of buffalo growth hormone (buGH), the equilibrium denaturation using guanidinium chloride (GdmCl) was carried out and was monitored by ultraviolet absorption spectroscopy, intrinsic fluorescence spectroscopy, far UV-circular dichroism and size-exclusion chromatography. The normalized denaturation transition curves for each of the above methods were not coincident, showing that buGH does not follow a simple two state folding mechanism. Further, size-exclusion chromatography also showed the presence of an associated intermediate during the unfolding of buGH. It was observed that in buGH, denaturation resulted in an initial disruption of the tertiary structure, whereas the secondary structure and the degree of compactness were disrupted at a higher concentration of the denaturant. This suggests that buGH follows the hierarchical model of protein folding.
Subject(s)
Animals , Buffaloes/metabolism , Circular Dichroism , Female , Growth Hormone/isolation & purification , Guanidine , Guanidines , Oxidation-Reduction , Pituitary Gland/metabolism , Protein Conformation , Protein Denaturation , Protein Folding , Spectrometry, Fluorescence , Spectrophotometry , Spectrophotometry, UltravioletABSTRACT
A purified preparation of growth hormone from pituitaries of water buffaloes (Bubalus bubalis) has been extensively characterized with regard to physico-chemical properties. The molecular size of buffalo GH (buGH) by electrospray ionization mass spectroscopy (ES-MS) was found to be 21394.00+/-8.44Da and its stokes radius was determined as 2.3 nm. Size heterogeneity in buffalo GH was checked both by electrophoresis and molecular sieve chromatography using 125I-labelled buffalo GH. Similar size heterogeneity was found in standard preparations of ovine and bovine growth hormones. Isoelectric focussing and chromatofocussing indicated charge heterogeneity in buffalo GH preparation. Major charge isoforms having pI of 7.2, 7.7 and minor forms in the pI range of 5.7 to 7.0 were found. Lectin chromatography on Concanavalin A matrix showed that less than 1% of buffalo GH was glycosylated. Heterogeneity in NH2-terminal sequence was also observed, with alanine, phenylalanine and methionine as the NH2-terminal residues as checked by dansyl and DABITC methods. Estimation of tryptophan residue indicated that a single tryptophan residue was present. Ellman's method showed presence of two disulfide bridges per mole of buffalo GH. Intrinsic fluorescence spectrum of buffalo GH exhibited lambda emission maximum at 337 nm. UV-CD spectrum showed that almost 48% of the secondary structure of buGH was constituted by alpha-helicity. The T(M) of buGH as determined by differential scanning calorimetric (DSC) studies was found to be 63 degrees C.