Purification, characterization and cloning of an aspartic proteinase inhibitor from squash phloem exudate.

Phloem exudate from squash fruit contains heat-inactivated material which inhibits pepsin activity. This inhibitory activity was purified by mild acid treatment, chromatography on trypsin-agarose, Sephadex G-75 and reverse-phase HPLC, resulting in the elution of three peaks with pepsin-inhibitory activity. N-terminal sequencing indicated a common sequence of MGPGPAIGEVIG and the presence of minor species with seven- or two-amino-acid N-terminal extensions beyond this point. Microheterogeneity in this end sequence was exhibited within and between two preparations. Internal sequencing of a major peak after a trypsin digestion gave the sequence FYNVVVLEK. The common N-terminal sequence was used to design a degenerate primer for 3' rapid amplification of cDNA ends and cDNA clones encoding two isoforms of the inhibitor were obtained. The open reading frames of both cDNAs encoded proteins (96% identical) which contained the experimentally determined internal sequence. The amino acid content calculated from the predicted amino acid sequence was very similar to that measured by amino acid analysis of the purified inhibitor. The two predicted amino acid sequences (96 residues) had neither similarity to any other aspartic proteinase inhibitor nor similarity to any other protein. The inhibitors have a molecular mass of 10,552 Da, measured by matrix-assisted laser-desorption ionisation time-of-flight mass spectrometry and approximately 10,000 Da by SDS/PAGE, and behave as dimers of approximately 21,000 Da during chromatography on Superdex G-75 gel-filtration medium. The calculated molecular masses from the predicted amino acid sequences were 10,551 Da and 10,527 Da. The inhibitor was capable of inhibiting pepsin (Ki = 2 nM) and a secreted aspartic proteinase from the fungus Glomerella cingulata (Ki = 20 nM). The inhibitor, which is stable over acid and neutral pH, has been named squash aspartic proteinase inhibitor (SQAPI).

IOL prediction: an evaluation of preoperatively determined intraocular lens power accuracy.

A retrospective survey of 612 eyes that had undergone cataract extraction and IOL implantation was undertaken to evaluate the accuracy of ultrasound biometry combined with keratometry using the SRK regression formula, for the preoperative prediction of intraocular lens powers. A mean error of +0.35 dioptre sphere (DS) (SD +/- 0.98) was found for the series overall, with a significant (P less than 0.005) difference between the distribution of postoperative refractive errors using the S.R.K. formula for IOL prediction and the use of a standard lens of 19.5 DS. The consistency of results was tested for those patients with greater or less than normal axial length. Linear regression analysis showed no correlation between axial length and postoperative refractive error and therefore does not support the adjustment of predicted IOL powers by a factor based on axial length. Statistically significant differences were found between surgeons' results, supporting the practice of A-constant modification for individual surgeons.

Efficacy and safety of hypromellose in ocular implant surgery.

In order to assess the efficacy of hypromellose as a viscoelastic substance in cataract surgery with posterior chamber intraocular lens implantation, we studied a series of 88 cases who underwent surgery with either alternate use of a viscoelastic substance (hypromellose, 39 patients, or sodium hyaluronate, 5 patients) or air (44 patients) in the anterior chamber. Endothelial cell loss was least in the group in which air was used (18 +/- 3% cell loss, mean +/- SEM), compared with hypromellose (26 +/- 3%) and sodium hyaluronate (28 +/- 6%), but the difference in percentage cell loss between the groups did not reach statistical significance. Some operative difficulties were encountered in both groups. In both the air and hypromellose groups there were two patients with an early postoperative rise in intraocular pressure, but this was easily controlled, and in both groups there were two patients with postoperative corneal oedema which soon cleared. Visco-elastic substances used in this study were not shown to be superior to air in protecting the corneal endothelium. For this reason use of hypromellose should be confined to situations where its use is likely to confer some special advantage, as in the presence of a bound-down pupil in patient's with chronic glaucoma or perhaps to facilitate "in the bag" implantation.

Vitreous cytology in primary cerebroretinal malignant lymphoma.

We report the case of a 72-year-old woman who presented with vitreous opacities of unknown cause. A pars plana vitrectomy yielded material in which there were atypical lymphoid cells consistent with malignant lymphoma. Five months after the vitrectomy, the patient re-presented with cerebral lymphoma. Our report emphasizes the value of cytological examination of the vitreous in selected cases. We also review the features of malignant lymphoma of the retina and stress the cerebroretinal axis of involvement in this disease.

See-saw nystagmus.

See-saw ocular movements are described in two patients, one having obstructive hydrocephalus and the other a thalamic infarct. Electro-oculographic studies demonstrated that the eye movements in patient 1 moved in and out of phase at irregular intervals, in both a horizontal and a vertical direction. The disconjugate eye movements were exaggerated in bright light and less evident during fixation. We suggest a lesion impairing the function of that circuitry of cells thought to include the nucleus centromedianus of the thalamus, the zona incerta, the interstitial nucleus of Cajal and eye movement related cells in the mid brain and pons, causes the disconjugate eye movements but that the controlling influence of multiple connections with other parts of the brain results in the ever changing pattern of disconjugate eye movement.