Other Variant Forms

In 1968, Fishman and his collaborators reported the identification of an ALP in the serum of a patient with metastatic squamous cell carcinoma of the lung that was biochemicaEy and immunologicaUy identical with the ALP of a normal placenta. The newly discovered isoenzyme was termed the Regan isoenzyme after the patient in whom it was discovered. The Regan isoenzyme has been detected in tumor tissues and in sera of patients with many types of malignant disease and in some patients with nonmalignant diseases. An incidence of the isoenzyme of 3% to 15% in sera of cancer patients has been estimated, but this varies with the sensitivity of the methods used for its detection. Other variant forms of ALP have since been discovered in tumor tissues. These variants show many similarities to normal placental ALP but may differ in other properties, such as response to certain inhibitors. 

Wadman, 1971). The possibility of double heterozygosity in these patients has been suggested (Scriver and Rosenberg, 1973 Zaleski etal, 1973). Other variant forms are much more rare, with a mild variant and patients with thiamin-responsive forms of the disease being described (Scriver and Rosenberg, 1973 Dancis and Levitz, 1978 Duran era/., 1978b Pueschal era/., 1979). A patient with valine toxic intermittent maple syrup urine disease has also been described (Zipf era/., 1979). 

In a variant of the horizontal form/fill/seal operation, the material, moving in a horizontal direction, is folded on itself vertically. Vertical sections of the two faces are heat-sealed to each other to form a pouch, which may then be filled. The pouch, usually made from film or paper bonded to aluminum foil plus a plastic laminant and heat sealant, is closed by a heat seal. This type of pouch gives high moisture and oxygen protection and is used for moisture-and flavor-sensitive condiments and beverage mixes. 

It was found inadvisable to use more than four molecules of form-amide [ (47) when R = H] per molecule of anthranilic acid and the condensation produces best results when the mixture is heated at 120 -130°C for 2 hr followed by further heating at 170°-180 C for 2 hr. Other variants of this reaction involve the use of ammonium o-acylaminobenzoates, anthranilic acid in the presence of nitriles and acetic anhydride, o-acetamidonitrile with acetic anhydride or hydrogen peroxide, anthranilic esters and aliphatic or aromatic amides or amidines, isatoic anhydride with amides or amidines, and anthranilic esters with aryl iminochlorides in acetoned The mechanism proposed by Bogert and Gotthelf has had experimental supporR and is represented in Scheme 12. 

The word may be a variant spelling. See Spelling, above, and look up other possible forms. 

Centronuclear myopathy with type 1 fiber hypotrophy is sometimes regarded as a separate entity because many cases show central nuclei only in the hypotrophic type 1 fibers, while the type 2 fibers are morphologically normal. Affected type 1 fibers are even more myotubelike than in other variants of the disorder, with the exception of the severe X-linked form, due to the persistence of a mitochondria-rich core within a peripheral ring of myofibrils. These features are clearly demonstrable using histochemical methods for the localization of SDH activity and myofibrillar ATPase, respectively. 

Protein kinase C (PKC) comprises the other major class of Ca2+-dependent protein kinases and is activated by Ca2+ in conjunction with DAG and phosphatidylserine (discussed in Ch. 20). Multiple forms of PKC have been cloned, and the brain is known to contain at least seven species of the enzyme. The variant forms of PKC exhibit different cellular distributions in the brain and different regulatory properties. For example, they differ in the relative ability of Ca2+ and DAG to activate them some require both Ca2+ and DAG, whereas others can be activated by DAG alone, apparently without an increase in cellular Ca2+ concentrations. However, these enzymes show similar substrate specificities and, as a result, are often considered isoforms. 

Some other variants are shown below, with their abbreviations. Pyroglutamic acid may be found where a terminal glutamic acid residue, linked to the chain through its carboxyl, forms a cycMc amide (lactam) (see Section 7.10). 

Each type of histone has variant forms, because certain amino acid side chains are enzymatically modified by methylation, ADP-ribosylation, phosphorylation, gly-cosylation, or acetylation. Such modifications affect the net electric charge, shape, and other properties of histones, as well as the structural and functional properties of the chromatin, and they play a role in the regulation of transcription (Chapter 28). 

All of the core histones share a conserved 65-residue histone fold.27 28 The arginine-rich histones have a strongly conserved amino acid sequence, histone H4 from pea seedlings differing from that of the bovine thymus by only two amino acids. On the other hand, the lysine-rich HI is almost species-specific in its sequence. Differentiated tissues contain at least seven variant forms of histone HI including proteins designated HI0, Hit, and H5 29-31... 

The next two entries to Table 3 are cited for completeness. Nitrogenase is treated in Chapter 7 and CO dehydrogenase in Chapter 9. Nitrogenase contains a very complex iron-sulfur cluster that includes another metal, molybdenum or vanadium. The crystal structure of the Mo variant has been determined. There is a third variant, alternative nitrogenase [92], whose cluster apparently does not contain any heterometal. That cluster would thus be a perfect candidate for our definition of a redox-catalytic iron-sulfur cluster. Unfortunately, this third nitrogenase has thus far been characterized to a much lesser extent than the other two forms. For all nitrogenases holds that the binding of N2 to the cluster has not been established [53] therefore, formally these enzymes have not yet been positively identified as redox iron-sulfur catalysts. 

Several other variants of GH have been described, particularly for the human hormone, including potentially the product of a second GH gene [132]. It remains uncertain, however, as to whether any of these has real significance or whether the normal (22K) form of GH is sufficient to explain all significant effects of the hormone, the variant forms being simply side products of little or no importance. 

Allele. One of the variant forms of a gene at a particular locus on a chromosome. Thus, different mutant allele means different mutations on the same gene and different mutants of the same gene are said to be alleles of each other. 

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