Hemorrhagic necrosis of pheochromocytoma associated with phentolamine administration.

A case of ruptured pheochromocytoma is presented, the pathophysiology discussed, and the literature reviewed. Evidence is presented that the use of alpha-adrenergic blockade in general, and phentolamine in particular, may predispose to this complication. Twelve cases of massive hemorrhagic necrosis with or without rupture were found in the literature, including the present case. Six had no operation; one survived. Six had immediate operation; 4 survived. An additional case of hemorrhage into a small pheochromocytoma following phentolamine is presented. This tumor was neither ruptured nor massively necrotic, but the case supports the hypothesis that alpha-adrenergic blockade may cause hemorrhage within the pheochromocytoma.

Conformational properties of bovine plasma albumin with a cleaved internal peptide bond.

As shown previously, proteinases frequently associated with plasma albumin samples catalyze a very limited and specific cleavage of the albumin molecule when it exists in the F conformational state near pH 3.7. The primary proteolytic product, BPA, has a molecular weight similar to or identical with that of the parent protein but yields two large fragments of molecular weight approximately 46000 and 23000 on reduction. Evidence is presented here that cleavage occurs within the disulfide loop between Cys390 and Cys434 with no detectable loss of small peptides, the amino acid composition of BPA being identical with that of the parent protein within experimental error. Cleavage exposes a new amino-terminal phenylalanine residue and may occur at the Glx392-Phe393 bond although the possibility exists that it occurs at another X-Phe bond in the unsequenced region of residues 400-402. The damaged protein has a somewhat altered secondary structure as judged from optical rotatory dispersion and circular dichroism measurements, probably an approximate 15% loss in helicity. The hydrodynamic volume is increased by approximately 20%. However, various physical studies indicate the tertiary structure to be strikingly similar to that of the native protein. Of most significance is the fact that the protein still undergoes the N-F and N-B transitions, although in both cases they occur at somewhat more moderate pH than in the parent protein. Moreover a sensitivity of the N-B transition to Ca2+ is still seen and binding behavior toward the dye 8-anilino-1-naphthalenesulfonic acid is essentially unaltered. The results are best understood in terms of the concept of a multidomain structure which has been suggested frequently for plasma ablumin. Bond cleavage damages one domain but leaves the overall structure essentially unaltered except for some weakening of the interaction between domains.

Limited hydrolysis of bovine plasma albumin at neutral and alkaline pH catalyzed by associated proteinases.

Proteinase contaminants in some plasma albumin samples have previously been shown to produce cleavage of the albumin molecule at acid pH. The F conformer, existing at pH 3.8, is cleaved near erisidue number 400 to yield a large N-terminal fragment of approximately 46,000 daltons. No cleavage was found at pH above approximately 4.4. It is shown in this paper that the proteinase contaminants are active over a broad pH range from 2.5 to 11.4 provided conditions are such as to induce some breakdown of the native conformation of the albumin molecule. Addition of Tris-borate buffer (0.1 M) at pH 7.5-9 is sufficient to permit cleavage. At pH near 9 this occurs predominantly 42,000 and 27,000 daltons. Near neutral pH substantial cleavage occurs in 4-8 M urea solution or in the presence of sodium dodecyl sulfate (AD110 complex). Under these conditions there are two large fragments (42,000 and 47,000 daltons) and essentially two small ones (20,000-27,000 daltons). Under conditions where there is no cleavage at 38-40 degrees, substantial cleavage results at 50-65 degrees but enzyme inactivation also occurs toward the top of this range. The alkaline activity is inhibited by soybean trypsin inhibitor but not by pepstatin; the reverse is true of the low pH activity. Cleavage at neutral or alkaline pH under the various conditions occurs primarily at X-Leu bonds while the low pH activity was already shown to occur at X-Phe. These facts suggest the presence of at least two enzymes. There is surprisingly little pH dependence over the range 7.5-9 in any of the media examined, even though albumin is known to undergo a significant conformational change in this range, the N leads to B transition. This transition is thought to be essentially a tertiary change with little loss of helix content. It is suggested that loss of native secondary structure, especially uncoiling of helical regions, is crucial to permit attack by these enzymes.

Photolysis accompanying peptide absorption in proteins. Electrophoresis and optical rotary dispersion studies.

Exposure of proteins and polypeptides to ultraviolet radiation below 240 nm produces peptide cleavage which may or may not be accompanied by observable changes in conformation and optical rotary dispersion (ORD) properties, depending on the stability of the secondary and tertiary structure of the macromolecule under the experimental conditions. Helical and coiled forms of poly-L-glutamic acid undergo degradation at similar rates but only the helical form shows a significant change in rotatory properties. The helical form of poly-L-lysine, but neither the coiled nor beta forms, shows a change in [alpha](233) on irradiation at 233 nm. beta-Lactoglobulin shows essentially no change in [alpha](233) on irradiation in either dilute salt solution or 4 M urea at room temperature; however, in 4 M urea at 56 degrees C a large change occurs. A model is developed which shows that studies of the effect of radiation on ORD properties may be useful in providing information on possible intermediate steps in protein denaturation. The method is illustrated with results on bovine plasma albumin. A quantum yield, 4.3 x 10(-3) moles/einstein, was obtained for peptide cleavage in this protein at 225 nm. These studies, based on gel electrophoresis, also showed that the fragments produced are essentially random, suggesting that transfer of energy from aromatic residues is not an important contributor to the peptide photolysis. Possible errors which could arise in ORD and other studies involving intense ultraviolet radiation are considered.