In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

Analysis of phenolic compounds of interest in metabolism.

1.1 Overview of the hyaluronidases
The hyaluronidases (Hyals) are classes of enzymes that degrade predominantly hyaluronan (HA). The term “hyaluronidase” is somewhat of a misnomer since they have the limited ability to degrade chondroitin (Ch) and chondroitin sulfates (ChS), albeit at a slower rate. It is a common misconception that the bacterial Hyals have absolute specificity for HA. This is incorrect. Both bacterial 1 and vertebrate enzymes degrade Ch and ChS, albeit at a slower rate. The plausible reason for this broader specificity is that chondroitins preceded HA in evolution. For example, the nematode, Caenorhabditis elegans, contains only Ch and no HA, with only one Hyal-like sequence (unpublished observations). This is most likely a chondroitinase. It is plausible, therefore, that the vertebrate Hyals evolved originally from pre-existing chondroitinases 1. This may explain why Hyals, recognizing their ancestral substrate, retain limited ability to also degrade Ch and ChS.

The Hyals from bacteria have been well characterized, and much information is available (for representative publications see 2–5). The Hyals in vertebrate tissues, on the other-hand, have not been studied extensively, however, due to the lack of structural information. Such studies were more difficult and, therefore, more limited. In addition, vertebrate Hyals are present at exceedingly low concentrations. In human serum, e.g., Hyal1 is present at 60 ng/ml 6. They have high specific activities that are unstable during the course of purification, requiring the constant presence of detergents and protease inhibitors for their isolation. Many of such difficulties have been overcome, and a great deal of information is now available, facilitated in part by the Human Genome Project 7.

Six Hyal sequences occur in the human genome, constituting a newly recognized family of enzymes. They have similar catalytic mechanisms that contrast markedly with the bacterial Hyals. There is growing interest in these enzymes as their HA substrate is achieving much attention. An outstanding review of the hyaluronidases was published 50 years ago by Karl Meyer, who was also the first to describe the chemical structure of HA 8. Interestingly, a chapter on mucopolysaccharidases, the former name for the hyaluronidases, was included in Volume 1 of Methods in Enzymology 9. The most recent overview of all of the Hyals appeared in 1971 10. Since that time, no comprehensive review has appeared.

Karl Meyer classified the Hyals into three distinct classes of enzymes 8, based entirely on the biochemical analyses available at the time. With the advent of sequence and structural data, we can now appreciate how remarkably accurate Karl Meyer’s classification scheme was. No modification of his formulation is necessary. There are three major groups of Hyals, based on their mechanisms of action. Two of the groups are endo-β-N-acetyl-hexosaminidases. One group includes the vertebrate enzymes that utilize substrate hydrolysis 11,12. The second group, which is predominantly bacterial, includes the eliminases that function by β-elimination of the glycosidic linkage with introduction of an unsaturated bond 2–4,13–17. As these enzymes catalyze the breaking of chemical bond by means other than hydrolysis or oxidation, and with the forming a new double bond they are also termed lyases. Both terms, the eliminase (or β-eliminase) and the lyase, are used in the review interchangeably. The third group are the endo-β-glucuronidases. These are found in leeches, which are annelids 18, and in certain crustaceans 19. No sequence data are available, and little is known about this potentially interesting class of enzymes. However, their mechanism of action resembles that of the eukaryotic or vertebrate enzymes more closely than the bacterial enzymes.

Sequence data for vertebrate Hyals now provide opportunities to formulate structure-function relationships, to examine probable mechanisms of catalysis, to identify putative substrate binding sites, and to consider the additional non-enzymatic functions of this family of multifunctional enzymes for two of the three groups, for the hydrolase and lyase types of Hyals, respectively 2. Such a review is presented here, documenting some of the common and some of the unusual features that distinguish each of these families of enzymes.

The primary objective of this review is to clarify what is known about the structure and mode of action of all the Hyals. Since so little is known of the leech-type of Hyals, the β-endoglucuronidases, the emphasis will, by necessity, be upon two of the three classes of enzymes. Other aspects of these enzymes, such as their physiological activities, their dependence on reaction conditions, their role in cell biology and involvement in metabolism, and their use as reagents or as therapeutics, are not the concern presently. A review of these other aspects of the Hyals will appear separately (Stern and Jedrzejas, in preparation).

High levels of HA turnover occur in vertebrate tissues. Tight regulation of catabolism is crucial for modulating steady state levels, important for normal homeostasis, and for embryonic development, wound healing, regeneration, and repair. Under pathological conditions, as in severe stress, shock, septicemia, in burn patients, following major surgery, massive injury, circulating HA levels increases rapidly. HA also increases in association with aggressive malignancies. Determining the mechanism of action of the Hyals is critical for understanding their controls over such a wide range of functions (for reviews, see 20,21).

/pdf/hyaluronidases-their-genomics-structures-and-mechanisms-of-3lts34acqe.pdf

Hyaluronidases: their genomics, structures, and mechanisms of action.

Intestinal alkaline phosphatase detoxifies lipopolysaccharide and prevents inflammation in zebrafish in response to the gut microbiota.

An improved automated procedure for the determination of calcium in biological specimens.

Summary In the course of a study of serum phosphatase isoenzymes in cancer patients, a patient with bronchogenic carcinoma was discovered, whose serum contained an alkaline phosphatase which was indistinguishable from placental alkaline phosphatase. The same enzyme was demonstrated in high concentration in the neoplasm and its metastases. This single case demonstrates the possibility that elevated serum alkaline phosphatase in patients with metastatic cancer can be of neoplastic rather than of hepatic and osseous origin.

https://cancerres.aacrjournals.org/content/canres/28/1/150.full.pdf

A Serum Alkaline Phosphatase Isoenzyme of Human Neoplastic Cell Origin

Derepression of the genome of the cancer cell may explain why certain cancer patients exhibit an isoenzyme of alkaline phosphatase biochemically and immunologically indistinguishable from human placental alkaline phosphatase.

Immunology and biochemistry of Regan isoenzyme of alkaline phosphatase in human cancer.

A method for estimating serum acid phosphatase of prostatic origin.

An alkaline phosphatase isoenzyme (Regan isoenzyme) has been identified in the serum of 27 patients with various malignant tumors. This isoenzyme is biochemically and immunologically indistinguishable from placental alkaline phosphatase. In addition to being present in serum, it has been identified in both tumor tissue and malignant effusion fluids. Measurement of this isoenzyme has been clinically useful in monitoring progression or regression of tumor, identifying a source of serum alkaline phosphatase elevation, and identifying malignant effusions.

Ectopic Production of an Alkaline Phosphatase Isoenzyme in Patients with Cancer

HUMAN alkaline phosphatase of intestine but not of liver, bile, bone, lung, kidney and spleen is almost completely (78 per cent) inhibited by L-phenylalanine and is not so affected by D-phenylalanine.

William H. Fishman

Papers

A Serum Alkaline Phosphatase Isoenzyme of Human Neoplastic Cell Origin

Immunology and biochemistry of Regan isoenzyme of alkaline phosphatase in human cancer.

A method for estimating serum acid phosphatase of prostatic origin.

Ectopic Production of an Alkaline Phosphatase Isoenzyme in Patients with Cancer

L -Phenylalanine : an Organ Specific, Stereo-specific Inhibitor of Human Intestinal Alkaline Phosphatase